**Table of Contents**

1\. INTRODUCTION [1-1](#need-for-stormwater-pump-stations)

1.1 Need For Stormwater Pump Stations
[1-1](#need-for-stormwater-pump-stations)

1.2 Intent of Manual [1-1](#intent-of-manual)

1.3 Organization of Manual [1-1](#organization-of-manual)

1.4 Unit Convention [1-1](#unit-convention)

1.4.1 SI versus Metric [1-1](#si-versus-metric)

1.4.2 Caution on Unit Usage [1-1](#caution-on-unit-usage)

2\. PUMP STATION COMPONENTS [2-1](#pump-station-components)

2.1 Introduction [2-1](#introduction-1)

2.2 Collection System [2-1](#collection-system)

2.3 Storage Unit [2-1](#storage-unit)

2.4 Wells [2-2](#wells)

2.5 Pumps [2-2](#pumps)

2.6 Pump Controls [2-2](#pump-controls)

2.7 Pump Drivers [2-2](#pump-drivers)

2.8 Station Housing [2-2](#station-housing)

2.9 Sump Pump [2-3](#sump-pump)

2.10 Power Supply [2-3](#power-supply)

2.11 Security and Access Features [2-3](#security-and-access-features)

2.11.1 Security [2-3](#security)

2.11.2 Access [2-4](#access)

2.12 Other Features [2-4](#other-features)

2.12.1 Hoists [2-4](#hoists)

2.12.2 Trash Racks [2-4](#trash-racks)

3\. PUMPS AND PUMP STATION TYPES [3-1](#pumps-and-pump-station-types)

3.1 Introduction [3-1](#introduction-2)

3.2 Classification of Pumps [3-1](#classification-of-pumps)

3.2.1 Dynamic Pumps [3-1](#dynamic-pumps)

3.2.2 Positive Displacement Pumps [3-1](#positive-displacement-pumps)

3.3 Impeller Types [3-1](#impeller-types)

3.3.1 Axial-Flow Pumps [3-2](#axial-flow-pumps)

3.3.2 Radial-Flow Pumps [3-2](#radial-flow-pumps)

3.3.3 Mixed-Flow Pumps [3-2](#mixed-flow-pumps)

3.3.4 Propeller versus Impeller [3-3](#propeller-versus-impeller)

3.3.5 Comparison of Impeller Types [3-3](#comparison-of-impeller-types)

3.4 Pumps For Stormwater Use [3-3](#pumps-for-stormwater-use)

3.4.1 Submersible Pumps [3-3](#submersible-pumps)

3.4.2 Vertical Shaft Pumps [3-4](#vertical-shaft-pumps)

3.4.3 Horizontal Pumps [3-6](#horizontal-pumps)

3.5 Wet-Pit Stations [3-7](#wet-pit-stations)

3.5.1 Vertical Pumps in Rectangular Wells
[3-7](#vertical-pumps-in-rectangular-wells)

3.5.2 Vertical Pumps in Circular Wells
[3-12](#vertical-pumps-in-circular-wells)

3.5.3 Submersible Pumps in Rectangular Wells
[3-13](#submersible-pumps-in-rectangular-wells)

3.5.4 Submersible Pumps in Circular Wells
[3-15](#submersible-pumps-in-circular-wells)

3.6 Dry-Pit Stations [3-18](#dry-pit-stations)

3.6.1 Dry Well [3-18](#dry-well)

3.6.2 Wet Well for Dry-Pit Station [3-19](#wet-well-for-dry-pit-station)

3.6.3 Storage Unit [3-19](#storage-unit-1)

3.7 Comparison of Pit Types [3-19](#comparison-of-pit-types)

3.7.1 Dry-Pit Station [3-19](#dry-pit-station)

3.7.2 Wet-Pit Station [3-20](#wet-pit-station)

3.8 Station Type Selection [3-20](#station-type-selection)

3.9 Debris and Sediment Handling [3-20](#debris-and-sediment-handling)

4\. PUMP STATION DESIGN PROCESS [4-1](#pump-station-design-process)

4.1 Introduction [4-1](#introduction-3)

4.2 Overview of Pump System Hydraulic operation
[4-1](#overview-of-pump-system-hydraulic-operation)

4.3 Pump System Design Objectives [4-2](#pump-system-design-objectives)

4.4 Pump Station Design Process Flowchart
[4-2](#pump-station-design-process-flowchart)

4.5 Planning Phase [4-5](#planning-phase)

4.5.1 General Planning Considerations
[4-5](#general-planning-considerations)

4.5.2 Level of Effort for Planning [4-5](#level-of-effort-for-planning)

4.6 Schematic Development Phase [4-6](#schematic-development-phase)

4.6.1 Data Collection [4-6](#data-collection)

4.6.2 Evaluation of General Facility Design Criteria and Constraints
[4-6](#evaluation-of-general-facility-design-criteria-and-constraints)

4.6.3 Evaluation of Alignment Alternatives and Value Engineering
[4-7](#evaluation-of-alignment-alternatives-and-value-engineering)

4.6.4 Roadway Profile Guidelines [4-8](#roadway-profile-guidelines)

4.7 Design Phase [4-8](#design-phase)

4.8 Development of Plans, Specifications and Estimates
[4-12](#development-of-plans-specifications-and-estimates)

4.8.1 Layouts and Details [4-12](#layouts-and-details)

4.8.2 Specifications, Provisions and General Notes
[4-12](#specifications-provisions-and-general-notes)

4.8.3 Design Review [4-12](#design-review)

4.9 Construction and Testing [4-13](#construction-and-testing)

4.10 Operation and Maintenance Phase
[4-13](#operation-and-maintenance-phase)

4.11 Retrofitting Stage [4-13](#retrofitting-stage)

5\. SITE PLANNING AND HYDROLOGY [5-1](#site-planning-and-hydrology)

5.1 Introduction [5-1](#introduction-4)

5.2 Considerations for Site Planning
[5-1](#considerations-for-site-planning)

5.2.1 Drainage Area [5-1](#drainage-area)

5.2.2 Proximity [5-2](#proximity)

5.2.3 Site Access [5-3](#site-access)

5.2.4 Power Sources [5-5](#power-sources)

5.2.5 Storage [5-5](#storage)

5.2.6 Environmental Quality [5-5](#environmental-quality)

5.2.7 Safety [5-6](#safety)

5.2.8 Security [5-7](#security-1)

5.2.9 Utilities [5-7](#utilities)

5.2.10 Soil Investigations [5-7](#soil-investigations)

5.3 Hydrologic Considerations and Criteria
[5-7](#hydrologic-considerations-and-criteria)

5.3.1 Premise for Design [5-7](#premise-for-design)

5.3.2 Design Frequency [5-8](#design-frequency)

5.3.3 Check Frequency [5-8](#check-frequency)

5.4 Design Hydrograph [5-8](#design-hydrograph)

5.4.1 Hydrologic Methods [5-9](#hydrologic-methods)

5.5 Procedure to Determine Mass Inflow
[5-10](#procedure-to-determine-mass-inflow)

6\. STORAGE SYSTEM [6-1](#storage-system)

6.1 Introduction [6-1](#introduction-5)

6.2 Storage Components [6-1](#storage-components)

6.3 Storage Concepts [6-1](#storage-concepts)

6.3.1 Storage Potential [6-1](#storage-potential)

6.3.2 Storage Design Philosophies [6-2](#storage-design-philosophies)

6.3.3 Available Storage [6-3](#available-storage)

6.3.4 Procedure to Estimate Total Available Storage Required
[6-3](#procedure-to-estimate-total-available-storage-required)

6.4 Collection System [6-4](#collection-system-1)

6.4.1 Procedure to Establish Collection System
[6-5](#procedure-to-establish-collection-system)

6.5 Maximum Highwater Elevation [6-5](#maximum-highwater-elevation)

6.5.1 Roadway Low Point [6-5](#roadway-low-point)

6.5.2 Hydraulic Grade Line [6-5](#hydraulic-grade-line)

6.5.3 Procedure to Determine Allowable Highwater in Wet Well
[6-6](#procedure-to-determine-allowable-highwater-in-wet-well)

6.6 Wet Well System [6-6](#wet-well-system)

6.6.1 Procedure to Select Preliminary Wet Well Dimensions
[6-7](#procedure-to-select-preliminary-wet-well-dimensions)

6.7 Storage Unit [6-7](#storage-unit-2)

6.8 Storage Calculations [6-8](#storage-calculations)

6.8.1 Sloping Conduit [6-9](#sloping-conduit)

6.8.2 Example of Storage in a Sloping Pipe
[6-10](#example-of-storage-in-a-sloping-pipe)

6.8.3 Procedure to Establish Storage Unit Dimensions
[6-11](#procedure-to-establish-storage-unit-dimensions)

6.8.4 Procedure to Develop Stage-Storage Curve
[6-12](#procedure-to-develop-stage-storage-curve)

7\. PUMP CONFIGURATION AND MASS CURVE ROUTING
[7-1](#pump-configuration-and-mass-curve-routing)

7.1 Introduction [7-1](#introduction-6)

7.2 Criteria and Considerations for Pump Configurations
[7-1](#criteria-and-considerations-for-pump-configurations)

7.2.1 Number of Pumps [7-1](#number-of-pumps)

7.2.2 Size of Pumps [7-1](#size-of-pumps)

7.2.3 Pump Sequencing [7-1](#pump-sequencing)

7.2.4 Pump Switching Elevations [7-2](#pump-switching-elevations)

7.2.5 Procedure to Estimate Capacity and Number of Pumps
[7-3](#procedure-to-estimate-capacity-and-number-of-pumps)

7.2.6 Pump Cycling [7-4](#pump-cycling)

7.2.7 Allowable Minimum Cycling Time
[7-4](#allowable-minimum-cycling-time)

7.2.8 Usable Storage [7-5](#usable-storage)

7.2.9 Pump Cycling Time [7-5](#pump-cycling-time)

7.2.10 Usable Storage Calculations [7-9](#usable-storage-calculations)

7.2.11 Procedure to Determine Trial Switching
[7-12](#procedure-to-determine-trial-switching)

7.3 Mass Curve Routing [7-15](#mass-curve-routing)

7.3.1 Procedure to Perform Mass Curve Routing
[7-16](#procedure-to-perform-mass-curve-routing)

7.3.2 Procedure to Check Routing Mass Curve
[7-17](#procedure-to-check-routing-mass-curve)

8\. DISCHARGE LINE AND PUMP SELECTION
[8-1](#discharge-line-and-pump-selection)

8.1 Discharge Line Components [8-1](#discharge-line-components)

8.1.1 Basic Line [8-1](#basic-line)

8.1.2 Manifold System [8-1](#manifold-system)

8.1.3 Design Size [8-1](#design-size)

8.1.4 Procedure to Determine Discharge Pipe Size
[8-2](#procedure-to-determine-discharge-pipe-size)

8.1.5 Pump Discharge Pipe Material and Configuration Guidelines
[8-2](#pump-discharge-pipe-material-and-configuration-guidelines)

8.1.6 Appurtenances [8-4](#appurtenances)

8.1.7 Preventing Reverse Flow [8-6](#preventing-reverse-flow)

8.1.8 Hydraulic Transients [8-6](#hydraulic-transients)

8.1.9 Accessories [8-6](#accessories)

8.1.10 Valves [8-6](#valves)

8.1.11 Flap Gates and Flap Valves [8-8](#flap-gates-and-flap-valves)

8.1.12 Outfall [8-10](#outfall)

8.1.13 Friction Loss Equations [8-11](#friction-loss-equations)

8.1.14 Appurtenance Energy Losses [8-13](#appurtenance-energy-losses)

8.2 Total Dynamic Head and System Curve
[8-15](#total-dynamic-head-and-system-curve)

8.2.1 Total Dynamic Head [8-15](#total-dynamic-head)

8.2.2 System Head Curve [8-16](#system-head-curve)

8.2.3 Procedure to Determine System Curves
[8-17](#procedure-to-determine-system-curves)

8.3 Pump Characteristics [8-21](#pump-characteristics)

8.3.1 Cavitation [8-21](#cavitation)

8.3.2 Vortexing [8-21](#vortexing)

8.3.3 Net Positive Suction Head Required
[8-22](#net-positive-suction-head-required)

8.3.4 Net Positive Suction Head Available
[8-22](#net-positive-suction-head-available)

8.3.5 Net Positive Suction Head Margin
[8-23](#net-positive-suction-head-margin)

8.3.6 Submergence [8-24](#submergence-2)

8.3.7 Specific Speed [8-24](#specific-speed)

8.3.8 Suction Specific Speed [8-24](#suction-specific-speed)

8.3.9 Selection of Impeller Type [8-25](#selection-of-impeller-type)

8.3.10 Pump Performance [8-25](#pump-performance)

8.3.11 Design Point and Operation Range
[8-27](#design-point-and-operation-range)

8.3.12 Example of Pump Selection [8-29](#example-of-pump-selection)

8.3.13 Procedure to Select Manufacturer's Pumps and Discharge Piping
[8-29](#procedure-to-select-manufacturers-pumps-and-discharge-piping)

8.3.14 Pump Bell/Intake Diameter [8-32](#pump-bellintake-diameter)

8.3.15 Power and Efficiency [8-32](#power-and-efficiency)

9\. SUMP DIMENSIONS AND SYSTEM CHECKS
[9-1](#sump-dimensions-and-system-checks)

9.1 Sump Size and Clearance Criteria
[9-1](#sump-size-and-clearance-criteria)

9.1.1 Sump Depth [9-1](#sump-depth)

9.1.2 Sump Width [9-1](#sump-width)

9.1.3 Submergence Depth [9-2](#submergence-depth)

9.1.4 Rectangular Sumps [9-2](#rectangular-sumps)

9.1.5 Circular Sumps [9-10](#circular-sumps)

9.1.6 Wet Well for a Dry-Pit Station
[9-16](#wet-well-for-a-dry-pit-station)

9.1.7 Reduced Intake Velocity [9-17](#reduced-intake-velocity)

9.2 System Checks [9-18](#system-checks)

9.2.1 Check Storage Volume [9-18](#check-storage-volume)

9.2.2 Check Cycling [9-18](#check-cycling)

9.2.3 Check Frequency [9-19](#check-frequency-1)

9.3 Backup Pumps [9-19](#backup-pumps)

10\. PUMP HOUSE FEATURES [10-1](#pump-house-features)

10.1 Introduction [10-1](#introduction-7)

10.2 Pump House Structure [10-1](#pump-house-structure)

10.3 Ventilation [10-2](#ventilation)

10.4 Walkways [10-3](#walkways)

10.5 Stairways and Ladders [10-3](#stairways-and-ladders)

10.6 Doors and Hatches [10-3](#doors-and-hatches)

10.7 Cranes and Hoists [10-3](#cranes-and-hoists)

10.7.1 Overhead Cranes [10-3](#overhead-cranes)

10.7.2 Monorails [10-4](#monorails)

10.7.3 Jib-Cranes [10-4](#jib-cranes)

10.7.4 Hoists [10-4](#hoists-1)

10.8 OSHA Requirements [10-5](#osha-requirements)

10.9 Fire Precautions [10-5](#fire-precautions)

10.9.1 Small, Unattended Stations [10-5](#small-unattended-stations)

10.9.2 Large Stations [10-5](#large-stations)

10.10 Security and Safety [10-5](#security-and-safety)

11\. BASIC ELECTRICAL AND MECHANICAL INFORMATION
[11-1](#basic-electrical-and-mechanical-information)

11.1 Introduction [11-1](#introduction-8)

11.2 Power Supply [11-1](#power-supply-1)

11.2.1 Electrical Mains [11-1](#electrical-mains)

11.2.2 Power from Generators [11-2](#power-from-generators)

11.2.3 Power Use [11-3](#power-use)

11.2.4 Electrical Power Factor [11-3](#electrical-power-factor)

11.3 Motors [11-3](#motors)

11.3.1 Other Motors [11-4](#other-motors)

11.3.2 Service Factor [11-4](#service-factor)

11.3.3 Motor Starting [11-5](#motor-starting)

11.3.4 Advantages of Using Electric Motors
[11-6](#advantages-of-using-electric-motors)

11.3.5 Disadvantages of Using Electric Motors
[11-6](#disadvantages-of-using-electric-motors)

11.4 Engines [11-6](#engines)

11.4.1 Engine Categories [11-7](#engine-categories)

11.4.2 Advantages of Using Engines [11-8](#advantages-of-using-engines)

11.4.3 Disadvantages of Using Engines
[11-8](#disadvantages-of-using-engines)

11.5 Backup Power [11-8](#backup-power)

11.5.1 Alternate Sources of Electrical Power
[11-8](#alternate-sources-of-electrical-power)

11.5.2 Backup Engines [11-10](#backup-engines)

11.6 Electrical Systems [11-10](#electrical-systems)

11.6.1 Protection Systems [11-10](#protection-systems)

11.6.2 Engine and Motor Switches [11-11](#engine-and-motor-switches)

11.6.3 Water Level Sensors [11-11](#water-level-sensors)

11.6.4 Sensing and Alarm Systems [11-13](#sensing-and-alarm-systems)

11.7 Mechanical Considerations [11-13](#mechanical-considerations)

11.7.1 Mechanical Packing [11-13](#mechanical-packing)

11.7.2 Minimizing Motor Wear, Tear, and Overheating
[11-14](#minimizing-motor-wear-tear-and-overheating)

12\. CONSTRUCTION, OPERATION AND MAINTENANCE
[12-1](#construction-operation-and-maintenance)

12.1 Introduction [12-1](#introduction-9)

12.2 Construction [12-1](#construction-1)

12.2.1 Safety [12-1](#safety-1)

12.2.2 Temporary Sediment Control [12-1](#temporary-sediment-control)

12.2.3 Contract Issues [12-1](#contract-issues)

12.2.4 Architecture [12-2](#architecture)

12.2.5 Aesthetics [12-2](#aesthetics)

12.2.6 Construction Materials [12-2](#construction-materials)

12.2.7 Pump Well Requirements [12-2](#pump-well-requirements)

12.2.8 Access to Pump Equipment [12-3](#access-to-pump-equipment)

12.2.9 Lifting Devices [12-3](#lifting-devices)

12.3 Pump Station Testing [12-3](#pump-station-testing)

12.3.1 Preliminary Considerations [12-3](#preliminary-considerations)

12.3.2 Preliminary Testing [12-4](#preliminary-testing)

12.3.3 Testing [12-4](#testing)

12.4 Operation And Maintenance [12-6](#operation-and-maintenance)

12.4.1 General Considerations [12-6](#general-considerations)

12.4.2 Safety [12-6](#safety-2)

12.4.3 Access to the Pump Station Site
[12-7](#access-to-the-pump-station-site)

12.4.4 Removal of Collected Debris and Sediment
[12-7](#removal-of-collected-debris-and-sediment)

12.4.5 Provision for Replacing Pumps
[12-7](#provision-for-replacing-pumps)

12.4.6 Typical Problems [12-7](#typical-problems)

12.4.7 Troubleshooting [12-7](#troubleshooting)

12.4.8 Inspection and Maintenance Schedule
[12-8](#inspection-and-maintenance-schedule)

12.4.9 Monitoring [12-9](#monitoring)

13\. RETROFITTING EXISTING SYSTEMS
[13-1](#retrofitting-existing-systems)

13.1 Introduction [13-1](#introduction-10)

13.2 Identification of Deficiency [13-1](#identification-of-deficiency)

13.3 Highway Modifications [13-1](#highway-modifications)

13.3.1 Increased Pumping Capacity [13-1](#increased-pumping-capacity)

13.3.2 Increased Storage Capacity [13-1](#increased-storage-capacity)

13.3.3 Elimination of the Structure
[13-2](#elimination-of-the-structure)

13.4 Poor Station Location Or Discharge Conditions
[13-2](#poor-station-location-or-discharge-conditions)

13.5 Hydraulic-Related Deficiencies of Pump Stations
[13-3](#hydraulic-related-deficiencies-of-pump-stations)

13.6 Replacement Of Pumps [13-3](#replacement-of-pumps)

13.7 Leakage [13-4](#leakage)

13.8 Modifications to Pump Switching
[13-5](#modifications-to-pump-switching)

13.9 Modifications to Wet Well [13-5](#modifications-to-wet-well)

13.9.1 Vortexing [13-5](#vortexing-1)

13.9.2 Cavitation [13-8](#cavitation-1)

13.9.3 Rapid Cycling [13-9](#rapid-cycling)

13.9.4 Excessive Sediment, Debris and Corrosion
[13-9](#excessive-sediment-debris-and-corrosion)

13.9.5 Replacing Wet Well [13-10](#replacing-wet-well)

13.10 Comparison Of Alternate Methods
[13-10](#comparison-of-alternate-methods)

14\. REFERENCES [14-1](#references)

Appendix A: GLOSSARY A-[1](#__RefHeading___Toc481572158)

Appendix B: ANNOTATED BIBLIOGRAPHY B-[1](#__RefHeading___Toc481572159)

Table of Figures

Figure 2‑1. Highway stormwater pump station
[2-1](#__RefHeading___Toc509049917)

Figure 2‑2. Highway stormwater pump house
[2-3](#__RefHeading___Toc509049918)

Figure 3‑1. Impeller types [3-2](#__RefHeading___Toc509049919)

Figure 3‑2. Submersible pump [3-4](#__RefHeading___Toc509049920)

Figure 3‑3. Vertical shaft-driven pump
[3-5](#__RefHeading___Toc509049921)

Figure 3‑4. Horizontal pump [3-6](#__RefHeading___Toc509049922)

Figure 3‑5. Vertical pump in rectangular wet well
[3-8](#__RefHeading___Toc509049923)

Figure 3‑6. Vertical pumps in rectangular well used by Arizona DOT.
[3-9](#__RefHeading___Toc509049924)

Figure 3‑7. Alignment of pumps in rectangular well
[3-10](#__RefHeading___Toc509049925)

Figure 3‑8. Typical suction umbrella
[3-11](#__RefHeading___Toc509049926)

Figure 3‑9. Small pump house for vertical pumps in Houston, Texas
[3-12](#__RefHeading___Toc509049927)

Figure 3‑10. Rectangular pit with submersible pumps
[3-14](#__RefHeading___Toc509049928)

Figure 3‑11. Large submersible pumps
[3-14](#__RefHeading___Toc509049929)

Figure 3‑12. Sample layout for submersible pumps in circular caissons
[3-15](#__RefHeading___Toc509049930)

Figure 3‑13. Circular wet well with submersible pumps -- elevation
[3-16](#__RefHeading___Toc509049931)

Figure 3‑14. Circular caisson wet wells under construction.
[3-16](#__RefHeading___Toc509049932)

Figure 3‑15. Circular caisson sump with submersible pump
[3-18](#__RefHeading___Toc509049933)

Figure 3‑16. Typical storage unit and dry-pit station
[3-19](#__RefHeading___Toc509049934)

Figure 4‑1. Pump station design process flowchart
[4-3](#__RefHeading___Toc509049935)

Figure 5‑1. Railroad underpass [5-2](#__RefHeading___Toc509049936)

Figure 5‑2. Pump station for a depressed section
[5-3](#__RefHeading___Toc509049937)

Figure 5‑3. Limited access to pump station from shoulder of highway
[5-4](#__RefHeading___Toc509049938)

Figure 5‑4. Driveway access to pump station in Arizona
[5-4](#__RefHeading___Toc509049939)

Figure 5‑5. Typical runoff hydrograph
[5-9](#__RefHeading___Toc509049940)

Figure 5‑6. Typical mass inflow curve
[5-12](#__RefHeading___Toc509049941)

Figure 6‑1. Hydrograph routed through pump station
[6-2](#__RefHeading___Toc509049942)

Figure 6‑2. Volume in storage at any stage
[6-3](#__RefHeading___Toc509049943)

Figure 6‑3. Estimate of storage required
[6-4](#__RefHeading___Toc509049944)

Figure 6‑4. Typical storage unit [6-8](#__RefHeading___Toc509049945)

Figure 6‑5. Ungula dimensions [6-10](#__RefHeading___Toc509049946)

Figure 6‑6: Example stage versus storage curve
[6-15](#__RefHeading___Toc509049947)

Figure 7‑1. Estimating total pumping rate
[7-4](#__RefHeading___Toc509049948)

Figure 7‑2. Cycling volumes [7-7](#__RefHeading___Toc509049949)

Figure 7‑3. Usable storage at any stage
[7-10](#__RefHeading___Toc509049950)

Figure 7‑4. Usable volume and pump start levels
[7-14](#__RefHeading___Toc509049951)

Figure 7‑5. Sample stage-discharge curve
[7-15](#__RefHeading___Toc509049952)

Figure 7‑6. Example of graphical method for mass curve routing
[7-17](#__RefHeading___Toc509049953)

Figure 8‑1. Typical flexible coupling
[8-5](#__RefHeading___Toc509049954)

Figure 8‑2. Ball float air valve [8-7](#__RefHeading___Toc509049955)

Figure 8‑3. Rubber flapper swing check valve
[8-8](#__RefHeading___Toc509049956)

Figure 8‑4. Typical flap gate [8-9](#__RefHeading___Toc509049957)

Figure 8‑5. Rubber check valve [8-10](#__RefHeading___Toc509049958)

Figure 8‑6. Typical outlet structure to channel
[8-11](#__RefHeading___Toc509049959)

Figure 8‑7. Components of total dynamic head
[8-16](#__RefHeading___Toc509049960)

Figure 8‑8. Typical system head curve
[8-16](#__RefHeading___Toc509049961)

Figure 8‑9. System curves for maximum and minimum static heads
[8-17](#__RefHeading___Toc509049962)

Figure 8‑10. Example system curve [8-20](#__RefHeading___Toc509049963)

Figure 8‑11. Types of vortex [8-21](#__RefHeading___Toc509049964)

Figure 8‑12. Net positive suction head available
[8-23](#__RefHeading___Toc509049965)

Figure 8‑13. Typical pump performance curve
[8-26](#__RefHeading___Toc509049966)

Figure 8‑14. Simplified manufacturer's pump performance curves
[8-26](#__RefHeading___Toc509049967)

Figure 8‑15. Design point [8-27](#__RefHeading___Toc509049968)

Figure 8‑16. Operating range for two pumps and common discharge line
[8-28](#__RefHeading___Toc509049969)

Figure 8‑17. Operating range for pumps with separate discharge lines
[8-28](#__RefHeading___Toc509049970)

Figure 8‑18. Manufacturer's performance curves
[8-29](#__RefHeading___Toc509049971)

Figure 8‑19. Pump manufacturer's curve
[8-31](#__RefHeading___Toc509049972)

Figure 9‑1. Recommended rectangular sump [9-4](#_Ref452692259)

Figure 9‑2. Filler walls for pump bay
[9-5](#__RefHeading___Toc509049974)

Figure 9‑3. Dimensions for sump example (NTS)
[9-8](#__RefHeading___Toc509049975)

Figure 9‑4. Confined rectangular wet well design
[9-9](#__RefHeading___Toc509049976)

Figure 9‑5. Circular sump -- two pumps on center
[9-11](#__RefHeading___Toc509049977)

Figure 9‑6. Circular sump -- two pumps off center
[9-12](#__RefHeading___Toc509049978)

Figure 9‑7. Circular sump -- three pumps on center
[9-13](#__RefHeading___Toc509049979)

Figure 9‑8. Circular well with sloping walls and minimized horizontal
floor area [9-16](#__RefHeading___Toc509049980)

Figure 9‑9. Sump dimensions for dry pit installation
[9-17](#__RefHeading___Toc509049981)

Figure 9‑10. Typical umbrella [9-18](#__RefHeading___Toc509049982)

Figure 10‑1. Typical pump house used by Texas DOT
[10-1](#__RefHeading___Toc509049983)

Figure 10‑2. Ventilation on Arizona DOT pump house
[10-2](#__RefHeading___Toc509049984)

Figure 10‑3. Overhead crane over wet well with submersible pumps
[10-4](#__RefHeading___Toc509049985)

Figure 11‑1. Liquid propane tanks for pump station power
[11-2](#__RefHeading___Toc509049986)

Figure 11‑2. Typical electric motors for vertical pumps
[11-4](#__RefHeading___Toc509049987)

Figure 11‑3. Engine drive [11-7](#__RefHeading___Toc509049988)

Figure 11‑4. Diesel-powered backup generator
[11-9](#__RefHeading___Toc509049989)

Figure 11‑5. Mobile generator and standby power receptacle
[11-9](#__RefHeading___Toc509049990)

Figure 11‑6. Tilting bulb switch [11-12](#__RefHeading___Toc509049991)

Figure 13‑1. Old motor drive for vertical pump to be replaced
[13-4](#__RefHeading___Toc509049992)

Figure 13‑2. Addition of baffles in sump
[13-6](#__RefHeading___Toc509049993)

Figure 13‑3. Pump realignment [13-7](#__RefHeading___Toc509049994)

Figure 13‑4. Addition of cone under intake
[13-7](#__RefHeading___Toc509049995)

Figure 13‑5. Addition of bell extension and splitter
[13-7](#__RefHeading___Toc509049996)

Figure 13‑6. Addition of backwall splitter
[13-8](#__RefHeading___Toc509049997)

Figure 13‑7. Addition of grouted transition
[13-8](#__RefHeading___Toc509049998)

**Table of Tables**

Table 5‑1. Development of cumulative inflow
[5-11](#__RefHeading___Toc509049849)

Table 6‑1. Storage properties of shapes
[6-9](#__RefHeading___Toc509049850)

Table 6‑2. Example stage storage table
[6-14](#__RefHeading___Toc509049851)

Table 7‑1. Suggested criteria for number of pumps
[7-1](#__RefHeading___Toc509049852)

Table 7‑2. Critical inflow rates for pump cycling
[7-8](#__RefHeading___Toc509049853)

Table 7‑3. Example usable storage table
[7-12](#__RefHeading___Toc509049854)

Table 7‑4. Pump switching table [7-15](#__RefHeading___Toc509049855)

Table 8‑1. Suggested pipe material selection
[8-3](#__RefHeading___Toc509049856)

Table 8‑2. Loss coefficients for pipe appurtenances
[8-14](#__RefHeading___Toc509049857)

Table 8‑3. Example TDH calculations [8-20](#__RefHeading___Toc509049858)

Table 8‑4. Vapor pressure heads for water
[8-23](#__RefHeading___Toc509049859)

Table 8‑5. Specific speed range for impellers
[8-25](#__RefHeading___Toc509049860)

Table 8‑6. Recommended pump intake velocities
[8-32](#__RefHeading___Toc509049861)

Table 8‑7. Specific weight of water [8-33](#__RefHeading___Toc509049862)

Table 9‑1. Rectangular sump dimensions
[9-3](#__RefHeading___Toc509049863)

Table 9‑2. Sample rectangular sump calculations
[9-6](#__RefHeading___Toc509049864)

Table 9‑3. Circular sump dimensions [9-10](#__RefHeading___Toc509049865)

Table 9‑4. Recommended sump inside diameter (D~s~)
[9-11](#__RefHeading___Toc509049866)

Table 11‑1. Recommendations for power use
[11-3](#__RefHeading___Toc509049867)

Table 12‑1. Pump operation problems and typical solutions
[12-8](#__RefHeading___Toc509049868)

Table 13‑1. Site problems and possible mitigation
[13-2](#__RefHeading___Toc509049869)

Table 13‑2. Possible causes of pump station deficiencies
[13-3](#__RefHeading___Toc509049870)

Table 13‑3. Mitigation measures for deficiencies related to vortexing
[13-6](#__RefHeading___Toc509049871)

**List of Symbols**

[Symbol]{.underline} [Description]{.underline} [Units, S.I.
(English)]{.underline}

*A* area of flow at uniform depth m^2^ (ft^2^)

*A~S\ ~*cross-section area of conduit m^2^ (ft^2^)

A distance from centerline of pump inlet bell/volute to sump entrance m
(ft)

a length of constricted bay section at pump m (ft)

*B* breadth (horizontal plane) m (ft)

*BP* brake power kW (hp)

B clearance from back wall to centerline of pump inlet bell/volute m
(ft)

*C~u~* unit conversion coefficient/factor \--

*C* unit coefficient/factor \--

C clearance between pump inlet bell and sump floor m (ft)

C~b~ minimum clearance between adjacent bells/volutes m (ft)

C~w~ minimum clearance between bell/volute and closest sump wall m (ft)

*D* diameter or rise m (ft)

*D* pipe diameter m (ft)

D outside diameter of pump bell/volute m (ft)

D~p~ diameter of inflow conduit m (ft)

D~s~ inside diameter of sump m (ft)

*d* deepest depth in element m (ft)

*f* friction factor \--

*g* acceleration due to gravity m/s^2^ (ft/s^2^)

*H* pump head at BEP m (ft)

*H~pa~* atmospheric pressure head on the surface of the liquid in the
sump m (ft)

*H~p~* pressure head change between outlet and intake m (ft)

*H~s~* static head m (ft)

*H~s~* static suction head of liquid m (ft)

*H~vp~* the vapor pressure head of the liquid at the operating
temperature m (ft)

H~min~ minimum water depth in sump m (ft)

h minimum height of constricted bay section m(ft)

*h~f~* friction head loss m (ft)

*h~l~* friction loss through appurtenance m (ft)

*h~V~* velocity head m (ft)

*Σh~f~* total friction losses in the suction line m (ft)

*K* loss factor based on standard data or manufacturer's specified data
\--

*L* length of pipe m (ft)

*L* length of element m (ft)

*L~s(req)~* total length of storage unit required m (ft)

L~p~ unobstructed straight length of inflow conduit m (ft)

*N* pump speed rpm

*N~ss~* suction specific speed rpm

N number of pumps in the station \--

*NPSHR* net positive suction head required m (ft)

*n* Manning's roughness coefficient \--

**List of Symbols (Continued)**

[Symbol]{.underline} [Description]{.underline} [Units, S.I.
(English)]{.underline}

*Q* discharge in pipe m^3^/s (cfs)

*Q* pump capacity at Best Efficiency Point m^3^/hr (gpm)

*Q~i~* a worst-case constant inflow rate for the particular pump cycle
m^3^/s (cfs)

*Q~p~* individual pump rate m^3^/s (cfs)

*Q~u~* discharge m^3^/s (cfs)

*R* hydraulic radius m (ft)

*S* slope of conduit m/m (ft/ft)

S minimum pump inlet bell submergence m (ft)

*s* slope of element m/m (ft/ft)

*s~s~* side slope (ratio of vertical to horizontal) m/m (ft/ft)

*TDH* total dynamic head m (ft)

*t* minimum cycle time minutes

*V* volume of element m^3^ (ft^3^)

*V~cs~* Volume in collection system below allowable highwater m^3^
(ft^3^)

*V~min~* minimum required cycle volume m^3^ (ft^3^)

V~n~ cycle volume for n^th^ pump m^3^ (ft^3^)

*V~req~* Minimum storage volume required m^3^ (ft^3^)

*V~s~* average velocity in pump bay m/s (fps)

*V~w~* Volume in wet well below allowable highwater m^3^ (ft^3^)

*v* flow velocity m/s (fps)

*W* width of element m (ft)

W pump inlet bay width m (ft)

w minimum width of constricted bay section m (ft)

*WP* water power kW (hp)

*WWP* wire-to-water power kW (hp)

X pump inlet bay length m (ft)

Y distance from centerline of pump inlet bell to screen m (ft)

Z~1~ distance from centerline of pump inlet bell to diverging walls m
(ft)

Z~2~ distance from centerline of pump inlet bell to sloping floor m (ft)

*α* angle of floor slope degrees

*β* angle of wall convergence degrees

*γ* specific weight of liquid N/m^3^ (lbf/ft^3^)

*η* pump efficiency \--

*η~e~* motor efficiency \--

*φ* angle of convergence from constricted area to pump bay walls degrees

# INTRODUCTION

## Need For Stormwater Pump Stations

Stormwater pumping stations are necessary for the removal of stormwater
from sections of highway where gravity drainage is impossible or
impractical. However, stormwater pumping stations are expensive to
operate and maintain and have a number of potential problems that must
be addressed. Therefore, the use of stormwater pumping stations is
recommended only where no other practicable alternative is available.
Alternatives to pumping stations include siphons, recharge basins, deep
and long storm drain systems and tunnels.

## Intent of Manual

This manual is intended primarily for highway drainage designers and
others interested in the hydraulic design of highway stormwater pump
stations. Though some discussion relates to other engineering
disciplines and responsibilities, the information is basic and intended
only to enhance the hydraulic designer's ability to accommodate other
needs and communicate with designers from other disciplines.

## Organization of Manual

This manual is divided into fourteen chapters including this
introduction. The general organization can be classified as follows:

1.  Identification and basic concepts (Chapters 2 and 3)

2.  Design process (Chapter 4)

3.  Design criteria, considerations, and procedures (Chapters 4 through
    9)

4.  Additional Information (Chapters 10 through 14, and appendices)

## Unit Convention

The general convention employed in this manual is to present values and
dimensions in System Internationale (SI) units followed by English units
in parentheses. Where practicable, the manual provides equations with
unit conversion factors. In this manner, only one equation appears for a
particular operation and the user must select the desired units and unit
conversion factor.

### SI versus Metric

System Internationale (SI) units are very specific. Not all metric units
are SI. For example, linear measurements of millimeters and meters are
metric and SI, whereas centimeters are metric but not SI. This manual
uses SI units except where noted to conform to industry standards.

### Caution on Unit Usage

Most manufacturers in the US develop pumps and pumping equipment in
English units. Few present design data in SI units. The designer should
take care when using and quoting units because some variables that are
seemingly dimensionless may have units. Some commonly used coefficients
have dimensions, which, in the strictest sense, should take on different
values when using SI units. These will be noted where appropriate
throughout the text.

# PUMP STATION COMPONENTS

## Introduction

This chapter identifies the major components of a highway stormwater
pump station. Figure 2‑1 shows a pump station and its major components.

![](media/image1.png){width="6.016666666666667in"
height="3.9451388888888888in"}

1.  []{#__RefHeading___Toc509049917 .anchor}Figure 2‑1. Highway
    stormwater pump station

## Collection System

Water is conveyed from the drainage area and highway to the pump station
in a system of ditches, gutters, inlets, and conduits that comprise a
collection system.

## Storage Unit

Many systems are designed to include an underground storage area using
box or circular conduits.

## Wells

All stations comprise a chamber (wet well) from which the stormwater is
pumped. Stations in which the pumps are placed in the wet well are known
as wet-pit stations. Some stations use a separate well (dry well) to
house the pump and driver and are referred to as dry-pit stations.

## Pumps

Pumps are devices that increase the static pressure of fluids. In other
words, pumps add energy to a body of fluid in order to move it from one
point to another. The increase in static pressure can be achieved in
different ways. Chapter 3 describes various pumps by which this result
can be achieved and the characteristics of such pumps.

## Pump Controls

The pump controls activate the pumps successively in response to a
rising water level in the sump. The controls regulate pump activity
until the inflow into the wet well has been evacuated.

## Pump Drivers

Electric motors and diesel, liquid propane gas, or natural gas engines
are used as pump drivers at stormwater pump stations.
Alternating-current electric motors are the most commonly used type of
driver. Engines are used infrequently because of the noise and
vibrations they produce.

## Station Housing

Figure 2‑2 shows a photograph of a typical pump house for a highway
stormwater pump station. General features of a pump house include:

-   ventilation,

-   doors and hatches,

-   stairs and ladders,

-   cranes and hoists, and

-   safety and security measures.

![](media/image2.png){width="4.971527777777778in"
height="3.3194444444444446in"}

[]{#__RefHeading___Toc509049918 .anchor}Figure 2‑2. Highway stormwater
pump house

## Sump Pump

A sump pump is sometimes installed in the sump of wet wells of wet-pit
and dry-pit stations. The sump pump is used to pump out the water
remaining in the well after the water level has dropped and all the
pumps are no longer pumping.

The sump pump may also remove the accumulation of solids, such as silt,
sand and debris that builds-up gradually at the bottom of the wet well.

## Power Supply

Electric power is usually the most economical and reliable power source
if it is available. Diesel, liquid propane, and natural gas are also
usually available to drive engines if no electrical service is available
or if there is an interruption in service.

Pumping stations also require a backup power source. The need or
requirement for standby power will vary with each installation and the
decision should be based on economics and safety. The three principal
types of backup power usually considered are multiple electric feeders,
engine-driven pumping units and electric generators.

## Security and Access Features

### Security

Pump stations usually include features to secure them from entry by
unauthorized personnel and to minimize the risk of vandalism. This may
be achieved by including as few windows as possible in the design,
providing fencing and exterior lighting, concealing expensive equipment
and installing unauthorized entry alarms.

### Access

Typical access features include:

-   off-highway driveways or service roads,

-   parking, and

-   loading zones.

## Other Features

### Hoists

Hoists are usually placed over basket screens, submersible pumps, other
pumps or motors, and other locations where it is necessary to lift heavy
pieces of machinery or equipment.

### Trash Racks

Trash racks may be provided at the entrance to the wet pit in order to
prevent large debris from entering the wet well.

#  {#section .unnumbered}

# PUMPS AND PUMP STATION TYPES

## Introduction

This chapter identifies the types of pumps and pump stations that are
used for highway stormwater drainage.

## Classification of Pumps

Pumps are often classified by the way in which they impart energy. The
two primary classes are:

-   dynamic or kinetic pumps, and

-   positive displacement pumps.

### Dynamic Pumps

Dynamic pumps are also called centrifugal pumps. The main feature of
this kind of pump is that the liquid is delivered in a continuous and
uninterrupted flow by means of an impeller - a rotating device with
vanes. The impeller transfers energy to the liquid being pumped, partly
by an increase in pressure, by producing a high liquid velocity greater
than the velocities occurring at discharge, and partly by an increase in
kinetic energy that is later converted into pressure energy.^1^

Dynamic Pumps may be divided into several varieties of centrifugal and
other special effect pumps (vertical shaft pumps). A common feature of
centrifugal pumps is that they are equipped with a volute or casing.

### Positive Displacement Pumps

Positive displacement pumps are those in which the moving element of the
pump forces a fixed volume of fluid from the inlet pressure section of
the pump into the discharge zone of the pump resulting in an increase in
the pressure of the liquid. Such pump types are seldom used for highway
stormwater pump stations and are not discussed further.

## Impeller Types

The three typical impeller types for pumps are axial, radial and mixed.
A description of each of these flow-types follows. Refer to Figure 3‑1
for identification of each type.

![](media/image3.png){width="4.290972222222222in"
height="4.1402777777777775in"}

[]{#__RefHeading___Toc509049919 .anchor}Figure 3‑3. Impeller types

### Axial-Flow Pumps

Pumps of the axial-flow type have impellers that lift the water up a
vertical riser pipe and direct the flow axially through the impeller
parallel to the pump axis and drive shaft (Figure 3‑1. a). Horizontally
mounted, axial-flow pumps are high-capacity pumps that are typically
used for low head, high discharge applications such as flood control.

### Radial-Flow Pumps

Radial (centrifugal) flow pumps have impellers that force the liquid to
discharge radially, from the hub to the periphery, by using centrifugal
force to move water up a riser pipe. Impellers of this type are called
radial flow or radial vane impellers (Figure 3‑1. b). The pumps handle
any range of head and discharge, but are most suited to high head
applications.

### Mixed-Flow Pumps

The mixed-flow type has impellers with vanes which are shaped such that
the pumping head is developed partly by centrifugal force and partly by
a lifting action of the vanes. They are either open type or closed type
(Figure 3‑1. c and Figure 3‑1. d respectively). The pumps are used
primarily for immediate head and discharge applications.

### Propeller versus Impeller

Propeller pumps are used for low-head pumping such as is typical for
highway stormwater pumping stations. The propellers are generally of the
vertical single-stage, axial- and mixed-flow type. Two-stage, axial-flow
pumps may also be used. Propellers are usually referred to as mixed-flow
impellers with a very small radial-flow component. A true propeller, in
which the flow strictly parallels the axis of rotation, is called an
axial-flow impeller.

Impellers are called radial vane or radial. As the impeller turns, the
centrifugal action creates a vacuum at the impeller "eye" and causes the
fluid to be discharged radially to the periphery with increasing
velocity. The high velocity at the blade tips is converted to pressure
in the casing. A higher impeller speed results in a higher blade
velocity, which means higher pressures. The impellers of centrifugal
pumps may be of the radial- or mixed-flow type.

### Comparison of Impeller Types

The following section lists some advantages and disadvantages associated
with different impeller types:

**Advantages**

-   Radial flow pumps with a single vane, non-clog impeller handle
    debris the best because of the large impeller opening.

-   Mixed-flow pumps deliver the liquid at a higher head than the
    propeller pump.

**Disadvantages**

-   Debris handling capability of radial-flow pumps decreases with an
    increase in the number of vanes.

-   The propellers of axial-flow pumps are susceptible to damage from
    large, hard objects.

## Pumps For Stormwater Use

### Submersible Pumps

Submersible pumps are close-coupled pumps driven by a submersible motor
and are generally a vertical type of pump. One vertical type of
submersible pump (Figure 3‑2) has a completely recessed impeller, out of
the stream of pumped liquid, while another has a specially shaped
non-clog impeller. The in-flow, non-clog impeller has substantially
higher efficiencies than the recessed impeller.

Submersible pumps require that the casing of the pump, which provides
the suction and causes the material to flow into the impeller blades, be
submerged in the liquid in order to pump. If the top cover is above the
level of the liquid then air will enter the casing and prevent liquid
from being discharged. When the casing is submerged, the pump will
self-prime and start pumping. Submersible pumps are designed to be
immersed in water and so are particularly suitable for wet well
installation and for use as sump pumps.

![](media/image4.png){width="4.889583333333333in"
height="2.9305555555555554in"}

[]{#__RefHeading___Toc509049920 .anchor}Figure 3‑4. Submersible pump

#### Advantages of Submersible Pumps

Some of the advantages of using submersible pumps include:

-   available size of submersible pumps, making it possible to design
    large stormwater stations with sole reliance on submersible pumps,

-   wide range of sizes and characteristics for a vertical propeller
    pump,

-   protection against dry well flooding,

-   easy removal for repairs,

-   elimination of need for long drive shafts,

-   natural cooling by stormwater, and

-   shorter allowable cycle times.

#### Disadvantages of Submersible Pumps

Some of the disadvantages of using submersible pumps are:

-   limited availability of motor sizes,

-   more expensive pump and motor,

-   need to operate in submerged conditions for cooling, and

-   potential need for larger wet well size and pump spacing.

### Vertical Shaft Pumps

Vertical shaft pumps, heretofore referred to as vertical pumps, are a
commonly used type of pump for stormwater pumping. The pumps are
equipped with an axial diffuser (or discharge bowl) rather than a
volute. The pump assembly of vertical pumps is suspended below the
baseplate by the necessary length of discharge column and elbow, with
the pump bowl being adequately submerged into the liquid being pumped
(Figure 3‑3).

The bowl assembly is the heart of the vertical pump and includes a
suction bell, discharge bowl, impeller, pump shaft, bearings and the
parts necessary to secure the impeller to the shaft. The suction bowl is
designed to permit proper distribution of the liquid to the impeller.
Vertical pumps for highway stormwater pumping stations will usually be
the single-stage, axial-flow type or the mixed-flow type.

![](media/image5.png){width="6.208333333333333in" height="4.0in"}

[]{#__RefHeading___Toc509049921 .anchor}Figure 3‑5. Vertical
shaft-driven pump

Typically, single-stage propeller pumps are used for low heads and
mixed-flow pumps for higher heads. A two-stage propeller pump
approximately doubles the head capacity of a single stage.

#### Advantages of Vertical Pumps

The advantages of selecting a vertical shaft pump for stormwater pumping
include:

-   low maintenance requirements,

-   easy access to the driver,

-   use of drive shafts up to 12-m (40-ft),

-   freshwater flushing of bearings as a viable lubrication alternative
    to grease where there is a municipal water supply, and

-   a small floor area which is sufficient to accommodate the axial pump
    bowl.

#### Disadvantages of Vertical Pumps

The disadvantages of selecting a vertical shaft pump for stormwater
pumping include:

-   questionable cost-effectiveness of water lubrication (because of the
    small number of annual operating hours of a stormwater pumping
    station and the relative ease of providing effective grease
    lubrication),

-   unsuitability of shallow sumps (due to submergence requirements),

-   requirement for two additional elbows for the vertical type,
    angle-flow pump \-- one in the suction and one in the discharge,

-   limited access to the pump, which requires pulling the entire
    assembly out of the pump station,

-   noise level, which is generally greater than for submersible pumps,
    and

-   shaft stretch, which wears impellers and bowls unless the thrust
    bearing is kept carefully adjusted.

### Horizontal Pumps

A horizontal centrifugal (non-clog) pump is shown in Figure 3‑4. Either
an electric motor or engine drives a horizontal shaft on which the pump
impeller is mounted. Usually, the impeller is housed in a spiral-shaped
casing called a volute. The unit is either frame-mounted or
close-coupled with the motor on the floor of a dry chamber (dry well).
Stormwater is collected in a separate chamber (wet well) and is
introduced into the pump through a suction pipe.

For highway pump stations, use of a horizontal pump usually implies
suction lift meaning that the intake pipe is lower than the centerline
of the axis of the impeller. Water is taken in along the impeller axis
and ejected perpendicular and vertical to the impeller axis.

![](media/image6.jpeg){width="5.539583333333334in"
height="3.736111111111111in"}

2.  []{#__RefHeading___Toc509049922 .anchor}Figure 3‑6. Horizontal pump

#### Advantages of Horizontal Pumps

The advantages associated with using a horizontal centrifugal pump at a
stormwater pumping station include:

-   high reliability,

-   mechanical and electrical simplicity of the horizontal centrifugal
    non-clog pump compared with the vertical shaft pump,

-   easy access for maintenance, since the pumps are placed in a dry
    well,

-   longer service life than vertical pumps,

-   less costly motors than for vertical pumps, and

-   lower headroom requirements than vertical pumps.

#### Disadvantages of Horizontal Pumps

Some of the disadvantages associated with using a horizontal centrifugal
pump at a stormwater pumping station are that:

-   the impellers typically have an efficiency of 70% or lower,

-   a dry well is required,

-   a large pump room floor area is required,

-   the motors are subject to flooding if the dry well becomes
    inundated, and

-   ventilation is needed to cool motors.

## Wet-Pit Stations

A wet-pit station typically comprises a wet well or several wet wells
and a pump house. Generally, one of two configurations is used:
rectangular or circular caisson. Two types of pumps, vertical and
submersible, may be installed in the wet well of the wet-pit station.

Vertical pumps are usually installed in either rectangular wells
(Section 3.5.1) or in circular wells (Section 3.5.2). Submersible pumps
are commonly installed in rectangular pits (Section 3.5.3). Simple
rectangular or circular wells are used for the smaller submersible pumps
(Section 3.5.4).

### Vertical Pumps in Rectangular Wells

Figure 3‑5 shows a simplified diagram of an installation of vertical
pumps in a rectangular well of a wet-pit station. Figure 3‑6 shows a
typical sketch of an installation used by Arizona DOT.

![](media/image7.png){width="4.970138888888889in"
height="3.623611111111111in"}

3.  []{#__RefHeading___Toc509049923 .anchor}Figure 3‑7. Vertical pump in
    rectangular wet well

![](media/image8.png){width="5.252083333333333in" height="6.5in"}

4.  []{#__RefHeading___Toc509049924 .anchor}Figure 3‑8. Vertical pumps
    in rectangular well used by Arizona DOT.

#### Alignment

Vertical pumps within a rectangular well are placed in a straight line
perpendicular to the direction of the flow, with a certain minimum
spacing between the pumps and back wall, depending on pump capacity and
bell diameters. Figure 3‑7 shows the recommended alignment. For criteria
on well dimensions, refer to Section 9.1 - Sump Size and Clearance
Criteria.

![](media/image9.wmf){width="3.4965277777777777in"
height="2.8777777777777778in"}

5.  []{#__RefHeading___Toc509049925 .anchor}Figure 3‑9. Alignment of
    pumps in rectangular well

#### Drive Shafts

The pumps are available with two different types of drive-shaft
construction and lubrication. These are: 1) pumps with oil-lubricated
line shaft bearings in an enclosing tube, which are the preferred
choice, and 2) pumps with open shafts and grease-lubricated bearings.

#### Trash Racks

When a trash rack is placed in the wet well, it is necessary to ensure
that there is an adequate distance between the trash rack and the back
wall of the wet well to ensure smooth flow to the pumps. Refer to
Section 9.1 - Sump Size and Clearance Criteria for recommended criteria.

#### Obstructions and Streamlining

A streamlined flow should be maintained throughout the length of the
pit. Generally, stairways and features other than trash racks and flow
directional vanes should not be placed in the flow path to the pumps.

Some configurations may require structural supports that extend down
into the sump and could interfere with the flow patterns. Such
interference could induce eddying and subsequent vortexing. To minimize
the potential for eddying, any necessary obstructions should be
streamlined and orientated to direct flow to the pumps.

#### Submergence

The depth of the sump is a function of the required submergence. Suction
umbrellas (Figure 3‑8) may be used to reduce the submergence
requirements. The umbrella provides a smooth transition for flow
entering the pump bowl. This helps reduce the potential for vortexing.

![](media/image10.png){width="4.279166666666667in"
height="1.0416666666666667in"}

6.  []{#__RefHeading___Toc509049926 .anchor}Figure 3‑10. Typical suction
    umbrella

#### Access

Provision must be made for access ladders, access holes, power operated
crane hoists and disposal of debris. Access should also be provided to
the area around the pump intakes for clearing and maintenance.

#### Provisions for Sediment-Laden Water

For rectangular wells, provisions to reduce potential problems with
sediment include:

-   designing the wet well to provide velocities of 1 m/s (3 ft/s) or
    higher -- though such an approach may require modeling and other
    provisions to reduce the potential for vortexing.

-   providing for violent mixing to suspend sediments (and removed by
    the main pumps). Measures include using submerged mixers and
    bypassing part of the pump discharge back into the well.

-   dewatering and pressure-cleaning the well.

-   designing a confined wet well. Refer to 9.1.4.6 Accommodation of
    Solids-bearing Water in Rectangular Wells.

#### Sump Pump

A sump pump is sometimes placed in wet wells and dry wells. Submergence
and clearance requirements will usually result in at least 1 m (3 ft)
depth of water remaining in the sump after the main pumps cease. Some
state highway agencies prefer to evacuate this water and any
sedimentation to help prevent clogging, excessive wear, and corrosion of
the main pumps.

#### Construction of Rectangular Well

The most common construction technique for a rectangular well is open
cut with sheet piling.

#### Pump House

The housing is usually above the wet well to enclose the pumps and
drivers and house the controls. Figure 3‑9 shows a sample of a small
pump house enclosing two vertical pumps in a rectangular wet well.

![](media/image11.png){width="4.973611111111111in"
height="3.3895833333333334in"}

7.  []{#__RefHeading___Toc509049927 .anchor}Figure 3‑11. Small pump
    house for vertical pumps in Houston, Texas

### Vertical Pumps in Circular Wells

#### Alignment

When placed in a circular caisson, the pumps should be placed with their
centers along the center of the sump or offset from the center of the
sump on the opposite half of the semicircle to the intake line.
Generally, a maximum of three pumps may be used in any one sump. For
criteria on well dimensions and configurations, refer to Section 9.1.5 -
Circular Sumps.

#### Driver Accommodations

Both electrically and engine-driven pumps may be used in circular wells.
When engines are used as drivers, the engines are housed in a separate
aboveground rectangular structure due to the limited space within a
circular caisson.

#### Submergence

The effectiveness of the layout and pump operation depends largely on
supplying ample submergence for the pumps. Submergence requirements
should be met by deepening the caisson.

#### Trash Racks

If trash racks are provided, they may be placed at the inlet side of the
sump or in a forebay or separate well. The trash racks should be easily
assessable due to the relatively small trash and debris storage
capability provided in the caisson.

#### Housing

As with vertical pumps in rectangular wells, the pump house encloses the
motors and other station equipment above the wet well.

#### Access

Provision must be made for access ladders, access holes, power operated
crane hoists and disposal of debris. There should also be access to the
area around the pump intakes for clearing and maintenance.

#### Provisions for Sediment-Laden Water

A quantity of the sand and silt that enters the station through the pit
inlets passes immediately through the pumps. For circular wet wells,
provisions to reduce potential problems with sediment include:

-   providing a separate well with sump pump with a lower floor than the
    main pumping well(s) to collect sediment,

-   using the storage system as a stilling area and making provision for
    removing the sediment, and

-   sloping the walls and minimizing horizontal floor space. Refer to
    9.1.5.5 Accommodation of Solids-bearing Water in Circular Wells.

In addition, for vertical pumps it will be preferable to provide a pump
lineshaft enclosing tube packed with a light hydraulic grease and
individual grease lines for each pump bowl bearing, with grease seals to
limit entrance of silt.

### Submersible Pumps in Rectangular Wells

Rectangular pump pits provide the most favorable conditions for flow
into and through the pit for submersible pumps. Large pumps can be
considered to have an individual capacity of greater than 680 m^3^/hour
(3000 gpm). The large vertical submersible pumps used in the rectangular
pit configuration may have as many as ten starts per hour. The
relatively high allowable number of cycles results in a lower required
storage volume than required for vertical pumps. Figure 3‑10 shows a
rectangular pit in which submersible pumps are installed. The pumps are
hung inside plastic piping and can be lifted from access holes above the
wet well. Divider walls help distribute the inflow and reduce the
potential for vortex formation. Figure 3‑11 shows the submersible pumps
prior to installation.

![](media/image12.png){width="5.970138888888889in"
height="3.9159722222222224in"}

8.  []{#__RefHeading___Toc509049928 .anchor}Figure 3‑12. Rectangular pit
    with submersible pumps

![](media/image13.png){width="5.8902777777777775in"
height="3.890277777777778in"}

9.  []{#__RefHeading___Toc509049929 .anchor}Figure 3‑13. Large
    submersible pumps

#### Housing

No elements of the wet well need appear above ground, so it is common to
provide a separate pump house for the controls, generator, and other
equipment. Alignment, flow distribution and clearance considerations are
similar to those described in Section 3.5.1 for vertical pumps in
rectangular wells. It is common and desirable to use an inlet chamber.

#### Inlet Chamber

An inlet chamber prevents the inflow from directly splashing into the
pump chamber and conveying air along with it. An overhang or hanging
baffle at the inlet of smaller pipes may be selected to prevent the
incoming water from directly splashing into the pump chamber. For larger
systems, the intake structures should be designed with adequate width
and depth to limit the maximum pump approach velocities to 0.5m/s (1.5
ft/sec). The horizontal axis of the inlet structure should be
perpendicular to the horizontal axis of the pumps and be positioned to
ensure even distribution of flow to the pumps without incurring eddies.

### Submersible Pumps in Circular Wells

Normally, there should be a minimum of two pumps installed in the well,
even though a single pump may provide the desired capacity. Figure 3‑12
shows a sample layout in which submersible pumps are placed in several
circular wet wells. The first wet well (Figure 3‑13) acts as a sump for
a sump pump and the other two wells house the main pumps.

![](media/image14.png){width="5.5in" height="2.667361111111111in"}

10. []{#__RefHeading___Toc509049930 .anchor}Figure 3‑14. Sample layout
    for submersible pumps in circular caissons

![](media/image15.png){width="5.248611111111111in"
height="2.8055555555555554in"}

11. []{#__RefHeading___Toc509049931 .anchor}Figure 3‑15. Circular wet
    well with submersible pumps -- elevation

#### Construction

A primary advantage of circular caissons is the efficiency with which
they can be constructed. Typically precast units are aligned and sunk
into the ground. Additional sections may be added as the first section
is lowered. The base is filled with in-situ concrete to provide ballast
as well as the sump floor. Figure 3‑14 shows caissons during
construction.

![](media/image16.png){width="4.945138888888889in"
height="3.376388888888889in"}

12. []{#__RefHeading___Toc509049932 .anchor}Figure 3‑16. Circular
    caisson wet wells under construction.

#### Storage Requirements

Small submersible pumps usually have a capacity of 680 m^3^/hr (3000
gpm) or less. Generally, for small submersible pumps, cycle times can be
as low as 2 minutes, resulting in significantly smaller system storage
requirements than other types of pump. Similarly, larger submersible
pumps have shorter minimum cycle times than many other pumps because of
the cooling resulting from the stormwater. This makes their use
preferable for situations in which there is little or no provision for
storage other than that provided by the wet well. However, for the
larger systems, storage outside the wet wells will reduce the size of
the pumps and is typically cost effective.

#### Pump Elevations

Some agencies may set the pumps at different elevations within the
caisson not only to provide for low-flow conditions but also to guard
against the build-up of sand or silt in the bottom of the pit, thereby
reducing the risk of damage to all the pumps. However, the pump set at
the lowest elevation may experience excessive wear because it must
always be the first and last to operate. Therefore, a preferred approach
is to set all the main pumps at the same elevation and add a pump of
smaller capacity than the main pumps.

#### Pump Configuration

Submersible pumps usually have bottom suction and side discharge. The
motor is commonly mounted vertically above the volute. The impeller is
then directly mounted on the motor shaft extension. The motor also may
be mounted horizontally, in which case water is drawn axially past the
motor and through the propeller into the discharge line.

#### Housing

Housing may not need to be above ground if controls can be placed in a
confined space with minimal spacing.

The arrangement of the pumps in circular caissons makes the removal of
any pump for maintenance or inspection easy. Removal becomes necessary
especially when the build-up of sand and silt reaches sufficient
quantity. The accessibility of the pumps makes the clean out of the
station a relatively simple operation. An agitating system may be
provided for a simple pit or caisson to ensure that the sump is cleaned.
The agitating system involves piping water into the caisson and
installing a spray ring system to agitate any sand and silt prior to
starting the pumps.

Sediment accumulation can be reduced by using sloping walls and
minimizing the amount of horizontal floor area.

#### Sump Pump

Some agencies prefer to place a sump pump either at the lowest point of
the main pump wet well or in a separate sump chamber. The layout shown
in Figure 3‑12 has a separate wet well that is used as a sump. Figure
3‑15 shows a sample detail of a sump pump in a circular caisson.

![](media/image17.wmf)

13. []{#__RefHeading___Toc509049933 .anchor}Figure 3‑17. Circular
    caisson sump with submersible pump

## Dry-Pit Stations

The dry-pit station comprises two main chambers: a dry well and a wet
well. The stormwater enters the station and is stored in the wet well.
The wet well is usually separated from the dry well by a wall and is
connected to the dry well by a suction line for each pump. The
stormwater pumps and controls are located on the floor of the dry well.
Power to the pumps is provided by either close-coupled motors in the dry
well or long drive-shafts with the motors located overhead.

### Dry Well 

The area of the dry well is usually rectangular in shape and the size
depends on the number of pumps installed in the well. The standard
design usually calls for a minimum of two pumps in series. Pumps are
usually of the horizontal centrifugal non-clog type. This type of pump
is suited for stormwater applications because it is resistant to wear
from abrasion. The pumps are oriented to provide both a clockwise and
counter-clockwise rotation to permit a symmetrical pumping arrangement.
The small size of the centrifugal pumps allows close spacing of the
pumps. Another advantage is the compact layout of the dry well, of which
only a small portion is occupied by the access shafts and switchgear.

Dry wells for dry-pit stations with vertical centrifugal angle flow
pumps, or vertical shaft centrifugal volute-type pumps as they are also
called, are usually more costly and require greater maintenance than
stations with horizontal shaft pumps. The reason for the added expense
and increased maintenance is the long drive shaft required between the
pump and the motor. The shaft is commonly a source of trouble due to
vibration.

### Wet Well for Dry-Pit Station

Wet wells for dry-pit stations are usually sized only large enough to
meet minimum sump clearance criteria (See Section 9.1 - Sump Size and
Clearance Criteria). The storage requirement for pump cycling criteria
is met by designing a storage unit or larger collection system. The
intake to the wet well should be designed to ensure even distribution of
flow to all the pumps. The bottom of the wet well is often dished in
order to direct the water to the suction line.

### Storage Unit

The storage unit for this arrangement is usually a multiple-barrel
culvert (Figure 3‑16) and usually connects to the wet well without
obstruction. The unit is set to a recommended slope of 2 percent to
minimize the potential for settlement of solids. The pumps effect an
almost complete emptying of the storage unit and sump with this
configuration.

![](media/image18.png){width="6.497222222222222in"
height="3.470138888888889in"}

14. []{#__RefHeading___Toc509049934 .anchor}Figure 3‑18. Typical storage
    unit and dry-pit station

## Comparison of Pit Types

The following sections cover the advantages and disadvantages of wet-pit
and dry-pit stations.

### Dry-Pit Station

#### Advantages of Dry-Pit Station

The advantages of selecting a dry-pit station include:

-   availability of a dry area for personnel to remove pumps or perform
    routine and emergency pump and pipe maintenance,

-   ease of access for repair and maintenance, and

-   protection of equipment from fire and explosion.

#### Disadvantages of Dry-Pit Station

Some of the disadvantages of selecting a dry-pit station are that:

-   construction is more expensive than wet-pit stations, and

-   they usually require a larger plan area than wet-pit stations.

### Wet-Pit Station 

#### Advantages of Wet-Pit Station

Advantages of selecting a wet-pit station are that:

-   some configurations require less surface area than dry-pit stations,

-   they are generally less expensive to construct than dry-pit
    stations, and

-   they allow for simpler details.

#### Disadvantages of Wet-Pit Station

Some disadvantages of selecting a wet-pit station include:

-   more limited access to pumps for maintenance than for dry-pit
    stations, and

-   required evacuation of water in wet well for pump maintenance.

## Station Type Selection

The choice of a wet-pit station or dry-pit station design is usually one
of individual or agency preference. Dry-pit stations are preferred when:

-   there is a high potential for health hazards to maintenance
    personnel,

-   there are concerns with the potential for fire or explosion, and

-   ease of maintenance is a major concern.

For highway stormwater pump stations, the use of wet-pit stations is
generally preferred by highway agencies. Primary reasons for this are:

-   availability of reliable, high-capacity submersible pumps which do
    not require a dry pit,

-   lower station construction costs, and

-   reduced site size requirements.

Generally, the selection of station and pump type is subjective and
often dependent on local preference and experience.

## Debris and Sediment Handling

Stormwater flushes the watershed and roadway before entering the
collection system carrying debris and sediment. The pumps should be
protected by screens to prevent passage of the larger debris and
provision should be made for accommodating sediment.

Screening may be provided by grate inlets or screened curb opening
inlets in the roadway gutters and ditches, or trash racks inside the
collection system, storage unit, or wet well.

One or more of several measures may be necessary to accommodate sediment
loads such as:

-   using an automatic flushing system and non-clog sump/sludge pump to
    evacuate sediment,

-   frequently flushing and pumping sediment in the system manually, and

-   designing sloping walls and minimizing horizontal floor area so that
    velocities will carry sediment to the pump intakes.

Provision should be made for handling hazardous material spills.
Preferably, the pump station should be isolated from the main collection
system and the effect of hazardous spills by a properly designed storage
facility upstream of the station. This may be a closed box below the
highway pavement or adjacent to it. The closed box must be ventilated by
sufficient grating area at each end. If the station collection system
design includes a closed conduit system leading directly from the
highway to the pump station without any open forebay to intercept
hazardous fluids or vent off volatile gases, there should be a gas‑tight
seal between the pump pit and the motor room in the pump station.

#### Trash Rack

Trash rack construction should follow the design criteria and
specifications listed below:

-   The rack should be fabricated from A36 structural steel. It is
    usually designed for convenience by designing the trash rack in
    modules with a number of similar panels.

-   A maximum clear‑space between bars of less than 40 mm (1.5 in.) is
    common in order to prevent passage of a large solid or similar
    object that might damage a pump.

-   The panels should be attached to the base slab with corrosion
    resistant stainless steel bolts and bolted at the top to the
    catwalk.

-   The pattern of the trash rack and a slightly sloping face should
    facilitate cleaning of the face by raking from the catwalk when
    necessary.

Trash racks in the wet well or storage unit or grate inlets in the
collection system should be provided to prevent large debris from
entering the sump.

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# PUMP STATION DESIGN PROCESS

## Introduction

This chapter provides an overview of the whole process for developing a
stormwater pump station design. It presents a general order and
description of what measures are taken. The design considerations and
specific procedures appear in Chapters 5 through 9.

The process can begin as early as during a Major Investment Study (MIS),
corridor study, or route and feasibility study. This chapter identifies
the following phases during which some level of effort may be required
for a pump station. These phases are:

1.  Planning

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5.  Facility Schematic Development

6.  Facility Design

7.  Plans, Specifications and Estimates (PS&E)

8.  Construction

9.  Operation and Maintenance

10. Retrofit

## Overview of Pump System Hydraulic operation

The following provides an overview of the hydraulic operation of a
typical stormwater pump system during a storm event to provide some
quick insight and act as a prelude to a detailed discussion of the pump
design process.

1.  Runoff enters the collection system and is conveyed to the storage
    unit and wet well of the pump station.

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```
11. For a period of time there is no outflow as the runoff is stored
    within the storage unit and wet well. The water level in the wet
    well rises and a hydraulic gradient develops based on the rate of
    inflow, the water level in the wet well, and the conveyance capacity
    of the storage unit and collection system.

12. The first pump starts when the water level in the wet well reaches a
    specific elevation. The pump evacuates the flow at a rate that
    varies with the pump characteristics and total dynamic head.

13. The inflow rate will vary as defined by the inflow hydrograph. If
    the pumping rate is lower than the inflow rate, the water level in
    the storage unit and wet well continues to rise and the volume
    stored in the system increases.

14. Additional pumps start at predetermined elevations as the water
    level rises.

15. At some point, the inflow rate will be lower than the total pumping
    rate. The water level in the wet well drops as water is evacuated
    from storage.

16. At preset elevations, as the water level drops, individual pumps are
    stopped and the discharge rate drops accordingly.

17. When the water level drops to the minimum level required for
    submergence, the last pump is stopped. The last pump off is usually
    the first to have been switched on, although different switching
    schemes are feasible.

Several observations can be made by inspecting the above process.

-   The number and/or size of pumps required drops with increasing
    available storage volume.

-   The peak outflow decreases with increasing storage.

-   The time between starts of a given pump (cycle time) is a function
    of storage volume, pump capacity and inflow rate.

-   If the pumping sequence, start and stop elevations, and pumping
    rates are not correct, the water level in the wet well will exceed
    the maximum allowable level.

-   If the pumping rates are too high or the start and stop elevations
    are improperly set, the water will be evacuated quickly and the
    pumps will operate too frequently.

## Pump System Design Objectives

Where practicable, it is preferable to avoid the need for a pump
station. However, when needed, pump system design is an iterative
process that has the following hydraulic objectives:

-   minimize inflow by keeping drainage area as small as practicable,

-   remove runoff from the highway system without exceeding critical
    elevations for design storm events,

-   comply with discharge constraints that may exist,

-   balance storage volume, pump size and number, and construction cost,
    and

-   select minimum cycle times that exceed allowable cycle times

## Pump Station Design Process Flowchart

The flowchart appearing in Figure 4‑1 maps out the phases and stages in
the stormwater pump station design process. The flowchart highlights the
iterative nature of pump design. For example, after the mass routing
stage, it may be necessary to adjust the storage unit, resize pumps,
change the number of pumps, or change the control elevations.

![](media/image19.wmf){width="13.475694444444445in"
height="8.597222222222221in"}

15. []{#__RefHeading___Toc509049935 .anchor}Figure 4‑19. Pump station
    design process flowchart

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## Planning Phase

The planning phase includes MIS, corridor studies and other route and
feasibility studies. This section provides discussion of the type and
level of effort that it is reasonable to expend to determine the need
for or viability of a stormwater pump station. Primarily this would be a
cursory level that would help identify constraints and other bases for
comparison of alternate alignments.

### General Planning Considerations

A detailed discussion of highway planning is beyond the scope of this
manual. However, the highway planners should be made aware that the
potential need for a stormwater pump station should be considered when
investigating alternative alignments. The high cost associated with
construction, operation, and maintenance of a pump station can often
render an alignment alternative undesirable.

When identifying potential highway alternative alignments, the planner
should consider any feasible alternatives that would not require a
stormwater pumping station. Whenever it is practicable, and other
constraints notwithstanding, the preferred alternative should avoid the
need for a stormwater pump station by ensuring adequate gravity
drainage.

### Level of Effort for Planning

The planning stage does not usually entail detailed engineering.
However, any planning should be performed in coordination with experts
from the various relevant disciplines. This should include the drainage
designer. Where an alternative is likely to involve a pump station, the
evaluation should include consideration of the following information if
available:

-   approximate drainage area required for pumping,

-   approximate right of way requirements for the station,

-   approximate right of way costs,

-   approximate maximum static head requirements,

-   average local pump station construction costs,

-   average local pump operation and maintenance costs, and

-   proximity to a discharge location.

An experienced pump station designer can use the drainage area and
static head information to provide an approximate pump system size.
Where average cost data are available, an "order of magnitude" estimate
of cost can be made, allowing the pump alternative to be included in an
alternatives matrix. The above discussion does not preclude the need to
address environmental issues that may relate to pump stations.

##  Schematic Development Phase

The primary objectives of schematic development are to:

-   establish a highway's vertical and horizontal alignment,

-   establish typical sections, and

-   identify general construction staging.

The schematic becomes the basis for the detailed design. Schematic
development is a critical phase in the highway development process,
after which the designer's ability to make significant changes becomes
severely limited. Therefore, consideration of the potential need for a
pump station should begin no later than during development of a
geometric schematic.

This section discusses the considerations and level of effort
appropriate for selecting a pump station. This includes:

-   data collection,

-   evaluation of general design criteria and constraints,

-   evaluation of alignment alternatives and value engineering, and

-   roadway profile guidelines.

### Data Collection

The following data should be collected and evaluated to determine if a
pump station is required and what the likely implications of vertical
alignment alternatives may be:

-   topographic maps/ survey data,

-   outfall locations and elevations,

-   approximate proposed roadway profile and horizontal alignment, and

-   approximate drainage areas.

### Evaluation of General Facility Design Criteria and Constraints

The designer should identify design criteria and typical constraints
that may affect the need for a pump station. Usually, the general
location of the highway is established during the planning phase. The
designer will then be limited to the alternatives that are available.
Typically, the following factors should be addressed:

-   programmed funds,

-   right of way availability and restrictions,

-   environmental constraints, and

-   Federal, State, and local regulations.

Funding will usually dictate the scope of a project and the options that
are available. Oftentimes, a no pump alternative can provide a less
costly project.

Right-of-way may be severely limited and the ability to acquire
additional right-of-way may be minimal. Pump stations can often be
designed for construction in limited space, but structural options
exist, such as bridges and elevated highways on retaining walls, which
can help minimize right-of-way requirements and avoid the need for pump
stations.

If environmental concerns such as noise and visual impacts are primary
factors, the alternatives may be limited. Political or public pressure
may also limit alternatives. However, the designer should still look for
the opportunity to avoid the need for a pump station.

### Evaluation of Alignment Alternatives and Value Engineering

Though there is a difference between evaluation of alternatives and
value engineering, they are essentially the same from the perspective of
the drainage designer. The objective is to establish the most
practicable and desirable drainage system. It is necessary to evaluate
alignment options to determine:

-   if a pump station can be avoided,

-   if a pump station is the most economical alternative,

-   if a pump station is the only feasible approach that meets design
    constraints/criteria, and

-   how the alignment can be developed to minimize stormwater runoff to
    the pump station.

The intent of such evaluation is to balance economy with reliability.
Generally, if a gravity system can be provided at a lower or similar
life cycle cost compared to a pump station, the gravity system option is
preferred. A gravity system is usually much more reliable than a pump
station.

Detailed design procedures are not envisioned here, but an evaluation of
the alternatives should be based on:

-   roadway profile alternatives,

-   highway vertical clearance requirements,

-   access to adjacent businesses and property,

-   outfall alternatives, and

-   current usage of pump stations by highway agency in local area.

#### Roadway Profile Alternatives

Roadway profile alternatives include comparison of feasible options such
as:

-   elevated versus depressed sections,

-   bridge structure and retaining wall for elevated sections versus
    retaining wall for depressed sections, and

-   at-grade alternatives.

Some alternatives such as at-grade solutions will likely be limited by
right-of-way restrictions. At-grade solutions may also be precluded by
functional needs such as:

-   multilevel directional interchanges,

-   grade-separated interchanges, and

-   railroad crossings.

#### Vertical Clearance

Vertical clearance requirements will depend on function and will affect
the roadway profiles, which affects the comparison of options. For
example, a highway underpass at a railroad will typically require lower
clearance for the highway traffic than the railroad will require for an
overpass. Thus the depressed section is likely to involve shorter
vertical curves than the overpass option.

#### Access to Abutting Property

The alignment alternatives must consider access to abutting businesses
and property. In some cases, an underpass and pump station combination
may provide the least interference to driveway and street intersections
for the same reason as discussed above. However, there are usually other
alternatives such as providing local access roads and detours.

#### Outfall Alternatives

Even if a depressed section provides the most effective highway
alternative, the designer should not automatically assume that a pump
station is the only feasible drainage solution. The pump station is
often considered necessary because the closest outfall is too high, or
the tailwater is too high. There may be other locations within the
watershed to which the depressed section could drain by gravity.

By evaluating the approximate potential life cycle costs of providing a
gravity storm drain to an alternate outfall, and providing a pump
station draining to the nearest outfall, the designer can determine
which option is reasonable. The evaluation should not just be limited to
construction costs. The construction cost of a gravity system could
exceed those of a pump station, but a typical gravity system will have
negligible to small operating and maintenance costs when compared to a
pump station. No specific cost data is provided here because costs vary
drastically by factors such as region, system type, construction method,
and maintenance methods.

### Roadway Profile Guidelines

Whenever a stormwater pump station is anticipated, the designer should
develop the roadway profile based on:

-   maximum practicable approach grades to the sag point,

-   minimum practicable vertical curve lengths to sag point, and

-   highest practicable sag point elevation.

These steps will minimize the roadway area that must drain to the sag
point, thus help reduce the required pump and storage system sizes.

##  Design Phase

The preceding phases identify the need for, and establish the viability
of, a stormwater pump station. The detailed design phase follows. This
section describes the stages in the process, in which the detailed
design of the pump station components is performed. Subsequent chapters
provide the criteria and detailed procedures. The discussion is
predicated on the assumption that the roadway geometry has been
established.

#### Field Survey and Data Development

The data collection needs are similar to those required for normal
drainage design of a highway project including establishing:

-   utility sizes, locations, and ownership,

-   outfall location, cross sections, profile grades, and roughness
    characteristics,

-   right-of-way locations,

-   roadway cross-sections, horizontal alignment, and vertical profile,

-   drainage area sizes and runoff characteristics,

-   collection system sizes, layout, and profile, and

-   tie-in elevations.

#### Stage 1: Site Planning

The site planning stage involves evaluating suitable locations for the
pump collection system, storage unit (if desired), and pump house. For
detailed considerations, refer to Section 5.2 - Considerations for Site
Planning.

#### Stage 2: Identification of Design Criteria

This stage involves establishing:

-   design frequency,

-   peak outflow (if appropriate),

-   station type (wet-pit station or dry-pit station),

-   design philosophy,

-   minimum storage volume,

-   maximum allowable highwater, and

-   discharge velocity.

The criteria must be established prior to proceeding with design of the
storage system and pump system. Refer to Chapter 6 for discussion on
these and other considerations.

#### Stage 3: Hydrologic Analysis

The hydrology stage involves determining:

-   drainage boundary and area,

-   runoff characteristics,

-   design runoff hydrograph(s), and

-   cumulative inflow.

The designer may begin hydrologic analysis after establishing the
roadway alignment and design criteria. State of the practice hydrologic
methods are employed such as appear in the FHWA publication Highway
Hydrology.^5^

#### Stage 4: Determination of Storage

This stage comprises designing or evaluating the following for providing
storage volume:

-   collection system,

-   storage unit, and

-   wet well.

#### Stage 4a: Collection System Design/Evaluation

The collection system stage establishes the collection system layout,
element sizes and shapes, and evaluates the storage in the collection
system between a maximum allowable high water and a minimum elevation in
the pump station. Some agencies specifically design parts of the
collection system by iteration to provide storage, in lieu of a bona
fide storage unit, to minimize the required pump capacity.

#### Stage 4b: Storage Unit Sizing

Many highway agencies design a specific storage unit to meet minimum
desired storage volumes or to optimize the required storage volume and
pumping capacity. If such a unit provides only the minimum required
volume, the sizing process can begin after the roadway alignment and
design criteria have been established. If optimal storage is to be
provided, the process may proceed as indicated in the flowchart, but
several iterations of storage unit sizing and pump configuration may be
necessary.

#### Stage 4c: Pit Dimensions and Wet Well Storage

One of two approaches is usually taken:

-   designer chooses a preliminary pit type and size, determines what
    pumps are needed, and then ensures clearances meet appropriate
    specifications for needed pumps, or

-   designer ignores wet well storage and establishes pump sizes and
    number, then sizes the pit based on appropriate criteria.

The approach is usually a matter of choice. Either approach will often
result in some level of iteration because the pump capacity is dependent
on total storage (of which wet- well storage is a component), and
wet-well storage is dependent on pit dimensions. Minimum pit dimensions
are dependent on pump number and capacity. When storage units are used,
the wet well storage is not usually the major part of system storage and
minor size adjustments may not alter the pump selection.

#### Stage 5: Trial Pumping Configuration

The design of a typical pump station is an iterative process. The only
condition under which a closed solution is likely is the combination of
a triangular/trapezoidal runoff hydrograph method and one pump. (A
minimum of two pumps is recommended for all highway pump stations.)

The process requires the designer to establish trial types, sizes and
numbers of pumps. The subsequent stages will evaluate the performance of
the trial configuration. If the configuration proves to be either
oversized or undersized, the designer must establish a new configuration
and repeat the evaluation.

The trial pump configuration may follow establishment of the design
criteria. The following table shows the necessary order of the design
process depending on the selected or required approach.

  ------------------------- ---------------------------------------------
  If the design approach is Then:
  to:                       

  Fix the peak outflow      The trial pump configuration may be
                            established after development of cumulative
                            inflow volume (mass inflow curve) and before
                            evaluating storage.

  Optimize storage/pump     The trial pump configuration should follow
  capacity                  hydrograph development and trial storage
                            system evaluation. A series of iterations of
                            storage size and pump configuration will be
                            necessary to establish which combination
                            achieves the best balance of pump size,
                            storage unit size, and construction cost

  Fix the storage volume    The trial pump configuration should follow
                            development of cumulative inflow volume and
                            trial storage system evaluation.
  ------------------------- ---------------------------------------------

#### Stage 6: Trial System Evaluation

The trial system evaluation stage includes various procedures to
determine whether or not the trial pump configuration and storage system
achieve the following objectives:

-   peak outflow equal to or lower than target peak (if appropriate),

-   highest water level in station does not exceed maximum allowable
    high water for design storm,

-   pump configuration is not excessive, and

-   selected pumps comply with manufacturer's specifications, such as
    cycling time and Net Positive Suction Head (NPSH).

The evaluation includes the following procedures, a suggested order of
which appears in the Design Process Flowchart:

-   development of inflow hydrograph,

-   development of mass curve from inflow hydrograph,

-   establishing trial storage unit size,

-   selection of initial wet well dimensions,

-   development of stage versus storage relationship,

-   establishment of usable storage,

-   establishment of trial pump switching/sequencing (cut-on, cut-off
    elevations),

-   mass curve routing,

-   routing sufficiency checks,

-   determination of Total Dynamic Head,

-   development of system head curves,

-   establishing an operation range,

-   establishing power requirements,

-   selection of pumps and piping from manufacturers\' performance
    curves and catalogue data,

-   performing cycle time checks, and

-   design optimization (balancing storage with pump type and size), if
    desired.

## Development of Plans, Specifications and Estimates

This phase (PS&E) involves developing the details, specifications, and
quantity estimates for the project.

### Layouts and Details

Site-specific layouts, special details, and standard details should
include the following:

-   general site layout,

-   collection system plan, profile, and details,

-   storage unit plan, elevation, and details

-   well plan, elevation, and details,

-   pump house plan, elevation, and details,

-   discharge piping and outfall plan, profile, and details, and

-   electrical and mechanical plans and details.

### Specifications, Provisions and General Notes

The designer should used standard specifications to the maximum degree
practicable. However, pump stations will usually require special
specifications, special provisions, and general notes to include items
such as:

-   pump performance specifications and tolerances,

-   pump installation and testing, and

-   special construction requirements.

Additionally, it is recommended practice to establish an operation and
procedures manual during PS&E that is to be used after construction of
the pump station.

### Design Review

The highway agency should provide an internal review of the design to
ensure:

-   adequacy of assumptions and criteria,

-   accuracy of calculations and details,

-   compliance with design criteria, policy and regulations, and

-   conformance with any commitments made in environmental documents
    (including Environmental Impact Statement or Environmental
    Assessment).

## Construction and Testing

This phase, though typically beyond the scope of the designer's
responsibilities, must be considered by the designer. Close coordination
is required between construction personnel and designers to ensure that
the design makes appropriate accommodation for construction needs and
that any lessons learned from construction can be transferred to the
designers.

Pump performance tests are conducted in place to ensure that pumps
perform as specified. Periodic tests during the operational life of the
station are appropriate to check continued operating efficiency of the
pumping station.

## Operation and Maintenance Phase

Operation and maintenance of pump stations involves frequent inspection,
monitoring, and maintenance. The highway agency should establish
operation and maintenance procedures and schedules. Some agencies
perform their own inspection and maintenance, while others pass on these
responsibilities to local agencies or independent contractors.

## Retrofitting Stage

The retrofit stage is inevitable for all stations that ultimately are
not completely replaced. Retrofit involves replacing various components
of the pump station, usually the pumps themselves. Hopefully this stage
is only necessary because the components of the station have passed
their design life expectancy. Refer to Chapter 13 -- Retrofitting
Existing Systems for a discussion of the need for retrofitting and
appropriate measures to take.

This page intentionally left blank.

#  {#section-1 .unnumbered}

# SITE PLANNING AND HYDROLOGY

## Introduction

This chapter discusses considerations for establishing suitable
locations for pump stations, identifies reference material for
hydrologic methods and presents some hydrologic criteria for design.

## Considerations for Site Planning

### Drainage Area

A primary consideration for the design of a stormwater pump station is
the drainage area. Pump station capacity requirements and associated
costs increase with increasing drainage area. Therefore, the designer's
goal should be to minimize the area that will drain to the proposed pump
station to the degree practicable.

The primary means of minimizing the drainage area are:

-   maximize roadway grades and minimize vertical curve lengths in the
    approach to the roadway low point(s) to reduce the length of roadway
    that drains to the low point(s),

-   use gravity storm drains as deep as practicable to drain as much
    surface area as practicable,

-   use retaining walls, where practicable, to minimize width of
    depressed roadway section, and

-   prevent offsite runoff from flowing to pump station using features
    such as berms and interceptor swales.

This approach is somewhat contrary to the typical goals of roadway and
storm drain design. Usually, flatter roadway grades are preferable to
steep roadway grades and shallow storm drains are preferred to deep
storm drains. The pump station designer must coordinate with the roadway
designer to ensure that the roadway design criteria are met.

Figure 5‑1 shows a railroad underpass in Houston, Texas that required a
pump station. Roadway profile grades were kept as steep as practicable
for the design speed in order to help reduce the drainage area. The
retaining wall, which was used because of limited right-of-way, also
helped reduce the drainage area. In addition, storm drain inlets were
used in the upper ends of the sag curve to direct as much flow as
possible away from the pump station collection system.

![](media/image20.png){width="4.986805555555556in"
height="3.332638888888889in"}

16. []{#__RefHeading___Toc509049936 .anchor}Figure 5‑20. Railroad
    underpass

### Proximity

The low point (or sag) for a highway stormwater pump station, is usually
at an underpass such as at a highway intersection or railroad crossing.
Generally, it is neither practicable nor preferable to place a pumping
station immediately adjacent to the low point of the highway because of
the following factors:

-   the station would usually be susceptible to flooding in the case of
    malfunction,

-   there would likely be an inadequate safety buffer for maintenance
    personnel,

-   the housing could pose a hazard to traffic,

-   potentially high construction costs, and

-   access to the station would likely be difficult or require
    interruption of traffic.

The station floor, on which the electrical equipment and other
facilities are placed, should be set at a higher elevation and the
housing situated away from the highway lanes. In the case of small
stations with submersible pumps, the wet well can reasonably be at the
low point, provided the electrical control panel is located on higher
ground. Suitable locations for the station include:

-   outside a frontage or service road,

-   between the highway main lanes and the frontage road,

-   at natural grade at the top of the cut slope of an underpass, and

-   on the berm within the easement of an outfall ditch.

The location of all features associated with the pump station should
conform to highway clear zone requirements.

The pump station shown in Figure 5‑2 is set above and away from the
roadway lowpoint.

![](media/image21.jpeg){width="5.0in" height="3.5972222222222223in"}

17. []{#__RefHeading___Toc509049937 .anchor}Figure 5‑21. Pump station
    for a depressed section

### Site Access

Pump stations require frequent inspection and maintenance. Therefore,
provisions should be made for easy access to the station and so that the
station is compatible with the number and size of vehicles and hoisting
equipment that will likely be required to construct and maintain the
station. Such provisions should include:

-   service road/driveway with suitable turning radii. See AASHTO's *A
    Policy on Geometric Design of Highways and Streets* for guidance,^7^

-   off-street parking,

-   station loading area,

-   turn around area,

-   space for heavy lifting equipment, and

-   roadside warning signs.

The site shown in Figure 5‑3 has poor access because there is no
vehicular access from ground level. Steps provide access from the
highway shoulder as can be seen in Figure 5‑2. It will be difficult to
replace any equipment, and traffic will be interrupted during any
significant maintenance.

![](media/image22.jpeg){width="5.570138888888889in"
height="3.6506944444444445in"}

18. []{#__RefHeading___Toc509049938 .anchor}Figure 5‑22. Limited access
    to pump station from shoulder of highway

The site shown in Figure 5‑4 provides safe access via a driveway,
without interfering with traffic. The depressed freeway is behind this
facility.

![](media/image23.jpeg){width="5.591666666666667in" height="3.7125in"}

19. []{#__RefHeading___Toc509049939 .anchor}Figure 5‑23. Driveway access
    to pump station in Arizona

### Power Sources

The designer should consider how power will be supplied. There will
usually be the need to supply electricity and sometimes natural gas. The
designer will need to communicate with appropriate power suppliers to
locate the site within easy reach of the power supply. If all power is
to be generated on site, then location concerns will relate primarily to
placing the site within easy access of a roadway for fuel supply.

### Storage

When considering the location of a highway stormwater pump station, it
is necessary to ensure that there is enough space between the highway
low point and the pump house to provide storage. Storage is an essential
component of a highway stormwater pump station because it allows the
designer to reduce the required total pumping capacity. A minimum
storage capacity is required to ensure that pump cycling criteria are
met. See Chapter 6 - STORAGE SYSTEM for detailed considerations of
storage components and the effect of storage. See Section 7.2.6 - Pump
Cycling for the effect of storage on cycling.

### Environmental Quality

During the planning phase, an Environmental Assessment (EA) or
Environmental Impact Statement (EIS) may be necessary. Usually, the
proposed pump station is incorporated into the study of a whole stretch
of highway improvement. Any commitments that are made in the EA or EIS
should be incorporated into the design.

Primary environmental quality issues to be considered include:

-   visual impact,

-   air quality,

-   noise attenuation, and

-   water quality.

#### Visual Impact

Most state transportation agencies now have on-staff or consultant
architects and landscape architects. It is preferable for the designer
to coordinate with such individuals to identify cost-effective ways of
enhancing visual quality. Typical low-cost measures include:

-   providing cut and embankment slopes of 1:3 or flatter,

-   allowing maximum areas of natural or planted vegetation,

-   enclosing unsightly objects such as storage tanks,

-   using submersible pumps to reduce the size of required above-ground
    facilities,

-   using local building materials that blend in with the surrounding
    architecture, and

-   providing underground utilities (power supply, phone lines, etc.).

#### Air Quality

To minimize potential air quality issues, where electrical generators or
engine-driven pumps are used, LPG or natural gas are preferred to
gasoline and diesel because they have cleaner byproducts (water vapor
and carbon dioxide). At the pump station site, the least impact results
from a purely grid-supplied electrical system.

#### Noise

Noise attenuation is often a primary concern near residential areas.
Where practicable, it may be desirable to minimize the potential for
noise pollution by taking one or more of the following measures:

-   use submersible pumps

-   where submersible pumps are not practicable, use electrically-driven
    motors

-   if engines are used, provide appropriate mufflers

-   build the pump house out of concrete or masonry

Sound insulation of the pump house walls may be an option; however, the
effectiveness of such a measure may be reduced by necessary station
ventilation.

#### Water Quality

Water quality issues have become more prevalent and require attention
for pump station design. For surface water, Environmental Protection
Agency (EPA) and state regulations will likely indicate the need for
some level of best management practices (BMPs) to help reduce the
potential for polluting receiving waters. The primary regulations are
the National Pollution Discharge Elimination System (NPDES) requirements
for construction (Industrial Activities) and NPDES Municipal Separate
Storm Sewer System (MSSSS) permit provisions. A highway stormwater pump
discharge is considered a non-point source just like a storm drain
outfall. Therefore, if the discharge point is within a municipality that
is currently operating under an MSSSS permit, the designer must ensure
that BMPs conform to the provisions of the permit by providing
appropriate features outside the pump station. The permit holder and
status will vary by state and municipality and the number of
municipalities covered by the NPDES requirements is subject to change.

### Safety

Safety must be a primary consideration for all pump station design and
should include provisions for:

-   construction personnel,

-   inspection and maintenance personnel,

-   motorists, and

-   the general public.

Provision for adequate access is a primary safety measure for inspection
and maintenance personnel. Other considerations include meeting OSHA
requirements for station access holes, hoisting, steps, ventilation etc.
Refer to Chapter 12 -- Construction, Operation and Maintenance for
additional discussion of inspection and maintenance considerations.

Primary means of ensuring public safety include:

-   minimizing traffic hazard by suitable site location (See Section
    5.2.2 - Proximity),

-   providing warning signs,

-   meeting clear zone requirements for the highway or providing
    appropriate protection,

-   providing adequate security (See Section 5.2.8 - Security), and

-   providing failure and high water level alarms.

### Security

A pump station is often an attraction for children and vandals. The site
should be protected both during and after construction. The primary
security measures are:

-   perimeter fencing,

-   intruder alarms,

-   concrete or masonry housing, and

-   locked louvered windows.

### Utilities

In addition to a power supply the following utilities are either
essential or preferred:

-   water supply,

-   sanitary sewer,

-   local storm drainage, and

-   phone line.

A potable water supply may be desirable to:

-   flush the sump,

-   facilitate cleaning of the station,

-   irrigate the station grounds, and

-   accommodate toilets and wash basins, if provided in the pump
    station.

### Soil Investigations

Consideration of local soil conditions and characteristics may affect
the proposed location of a pump station. The hydraulic designer should
coordinate the site planning with a geotechnical engineer to ensure that
the proposed location is not likely to encounter significant problems
associated with water table levels, soil bearing capacities, plasticity,
and seismic activity. For example, clay with water-bearing, sand lenses
can pose problems when constructing the pump sump, especially for sunk
caissons which can experience differential settlement. The geotechnical
engineer also may suggest construction methods that are appropriate for
the soil conditions.

## Hydrologic Considerations and Criteria 

### Premise for Design

A highway stormwater pump system is designed to remove runoff from the
highway system without inundating the highway under design conditions.
Usually the drainage collection points are in depressed sections so that
there is no relief location to which the runoff may drain. Therefore, a
typical highway stormwater pump station should be designed to
accommodate not just frequent runoff events but also less frequent
events.

### Design Frequency

The recommended design for a highway stormwater pump station is a return
period of 50 years with the following qualifications:

-   mandatory for interstate highways,

-   may be reduced or increased if supported by risk assessment,

-   may not be practicable for retrofit pumps, and

-   where the pump is used to isolate the highway from the backwater
    effects of a receiving water, the designer should consider the
    implications of joint probabilities of flooding on the highway
    system and the receiving water.

### Check Frequency

The standard check flood is one having a return period of 100 years. The
primary intent of this check is to identify the potential risks
associated with inundation during such an extreme event and ensuring
conformance to Federal Emergency Management Agency (FEMA) National Flood
Insurance Program (NFIP) criteria.

In addition, it is recommended that a frequent event, such as a 2-year,
be used to check low flow operation so as to ensure that no excessive
cycling is likely.

## Design Hydrograph

The design runoff hydrograph is the basis for sizing a highway
stormwater pump system. Figure 5‑5 shows a typical design inflow
hydrograph. The method used should be applicable for the conditions to
be addressed and based on the design frequencies discussed above. Refer
to the FHWA publication "Highway Hydrology", HDS 2,^5^ for detailed
considerations and procedures for determining runoff hydrographs.

![](media/image24.wmf){width="5.225694444444445in"
height="3.4652777777777777in"}

20. []{#__RefHeading___Toc509049940 .anchor}Figure 5‑24. Typical runoff
    hydrograph

### Hydrologic Methods

The choice of hydrologic methods is either based on agency standard
practice or left up to the designer based on local conditions and
judgment. Specific methods often used by state highway agencies include:

-   National Resources Conservation Service (NRCS) -- formerly Soil
    Conservation Service) -- Tabular Hydrograph Method of *Technical
    Release 55,* *Urban Hydrology for Small Watersheds* (TR55),^8^

-   NRCS dimensionless unit hydrograph method based on *Technical
    Release 20, Hydrology*, (TR 20),^9^ and

-   Methods available in the computer programs HEC-1 and HEC-HMS.

#### NRCS Methods

The TR 55 tabular approach is simple and often sufficient. With the
availability of powerful computers, spreadsheets, and hydrologic
software, hydrographs from methods such as the TR 20 method are simple
and quick enough to generate and are more accurate (TR 55 is a
simplification of TR 20). However, when using TR 20, the designer should
consider the validity of using long duration rainfall events, such as 24
hours. Shorter duration storms that compare with the estimated time of
concentration for the drainage area are usually more appropriate for
pump station design. The TR 20 method is applicable to shorter duration
events if an appropriate design rainfall distribution is available.
Standard rainfall hyetographs for the country are limited to 6-hour and
24-hour durations.

#### Other Methods

Other local methods may be used when the agency is comfortable that the
discharge versus frequency relationships are statistically based and the
method allows the designer to choose an appropriate design rainfall
duration.

## Procedure to Determine Mass Inflow 

A mass inflow curve represents the cumulative inflow volume with respect
to time. In order to determine a mass inflow curve, the designer first
must have developed an inflow hydrograph. The following describes how to
develop a mass inflow curve.

1.  Evaluate the time base of the design hydrograph and select a time
    increment. Usually, the designer uses the same time increment as
    that used for developing the inflow hydrograph.

```{=html}
<!-- -->
```
1.  Develop a table of time, time increment, inflow rate, average inflow
    rate, incremental inflow volume and cumulative inflow volume as
    shown in Table 5‑1.

2.  At each time step, take the inflow rate from the computed inflow
    hydrograph. See Column 3 in Table 5‑1.

3.  Compute and tabulate the average inflow rate as half of the sum of
    the current and previous inflow rates for each time step. See Column
    4 in Table 5‑1.

Example: using Table 5‑1, the average inflow at time = 5 mins is:

(0 + 0.003) / 2 = 0.0015 m^3^/s (0.053 cfs)

4.  Compute and tabulate the incremental volume for each time step as
    the average inflow rate multiplied by the time increment (in
    seconds). See Column 5 in Table 5‑1.

Example: using Table 5‑1, the incremental inflow volume at time = 5 mins
is:

0.0015 m^3^/s x 5 mins x 60 secs/min = 0.45 m^3^ (1.48 ft^3^)

5.  Compute and tabulate the cumulative volume for each time step as the
    sum of the incremental volume in the current time step and the
    cumulative volume of the previous time step. See Column 6 in Table
    5‑1.

Example: using Table 5‑1, the cumulative inflow volume at time = 5 mins
is:

0 + 0.45 = 0.45 m^3^ (1.48 ft^3^)

6.  Plot a curve of cumulative volume versus time. The result is a mass
    inflow curve.

Example: Refer to Figure 5‑6 which is based on Table 5‑1.

21. []{#__RefHeading___Toc509049849 .anchor}Table 5‑1. Development of
    cumulative inflow

![](media/image25.wmf){width="5.086805555555555in" height="6.1in"}

![](media/image26.wmf){width="5.454861111111111in"
height="3.729861111111111in"}

22. []{#__RefHeading___Toc509049941 .anchor}Figure 5‑25. Typical mass
    inflow curve

#  {#section-2 .unnumbered}

# STORAGE SYSTEM

## Introduction

The biggest distinction between highway stormwater pump stations and
other pump systems is the significant use of storage. This section:

-   identifies the components of the system that provide storage,

-   indicates criteria used to establish storage, and

-   provides guidance on sizing storage elements.

## Storage Components

The storage components of a highway stormwater pump station include:

-   the collection system,

-   the storage unit, and

-   the wet well system.

## Storage Concepts

### Storage Potential

The design of stormwater pump stations is analogous to the concept of
stormwater detention. In other words, the rate of outflow is the
difference between the rate of inflow and the rate of change of volume
stored. For typical detention ponds, as the storage volume increases,
the peak outflow rate decreases. For a pump station, as the storage
volume increases, the required pumping capacity decreases. Figure 6‑1
shows a typical inflow hydrograph routed through a pump station. The
area bounded by the rising limbs of the inflow and outflow hydrographs
represents the total volume in storage.

For a particular design inflow hydrograph, the peak pumping capacity
requirements reduce with increasing storage. At one extreme, if no
storage were available, the pump system would be required to discharge
at the same rate as the inflow, requiring a large number of
varied-capacity or variable speed pumps and expensive, complex control
systems. At the other extreme, if the storage exceeded the inflow
volume, only a low flow pump would be required to evacuate the system,
but the cost of storage would likely be excessive. Somewhere in between,
there is an optimal condition for a particular site that balances the
storage provided with the size and number of pumps.

23. 

![](media/image27.wmf){width="6.477777777777778in"
height="3.2895833333333333in"}

24. []{#__RefHeading___Toc509049942 .anchor}Figure 6‑26. Hydrograph
    routed through pump station

### Storage Design Philosophies

There are three general approaches to pump system storage and pump
sizing.

-   Size the collection system for adequate conveyance of the runoff
    using conventional storm drain design procedures (See FHWA's *Urban
    Drainage Design Manual*^10^*).* Choose a wet well size, size the
    pumps and set the pump switching to maximize use of the provided
    storage.

-   Identify a target outflow rate and choose pumps that have a total
    capacity of the target outflow rate. Establish the required system
    storage to detain the design inflow hydrograph. This approach may be
    used in areas where ordinances limit peak discharges to
    pre-developed rates, or where the outfall system has limited
    capacity.

-   Using iteration, vary the storage volume, pump sizes and number of
    pumps to determine a combination that minimizes total life-cycle
    cost. This is a more time-consuming approach but will most often
    produce the best overall design.

The latter approach is preferred since neither of the other two
approaches identify the combination of pump size and storage that
minimizes life-cycle costs.

The primary effect of storage is to attenuate peak discharge rates.
Additionally, storage affects the frequency of pump operation (pump
cycling times). As storage volume increases, the cycling time increases.
Longer cycling times are preferred and design cycling times must exceed
manufacturer's specified minimum cycling times. Therefore, it will be
necessary to ensure that either enough storage is provided for a
specific system of pumps, or a system of pumps and sequencing scheme is
developed to accommodate the storage.

### Available Storage 

The total storage volume in the collection system, storage unit, and wet
well between the lowest pump operation elevation and the maximum
allowable high water serves to detain the inflow. This total storage
volume is termed total available storage in this document.

At any stage, H, the volume used for storage of the inflow is the volume
between the water level and the lowest pump operation elevation (Stage =
0) as shown in Figure 6‑2. The available storage is independent of
inflow rate if the hydraulic grade line is ignored. See Column 5 in
Table 5‑1

![](media/image28.wmf)

25. []{#__RefHeading___Toc509049943 .anchor}Figure 6‑27. Volume in
    storage at any stage

### Procedure to Estimate Total Available Storage Required

1.  Select a design inflow hydrograph

2.  Choose trial target total pumping rate.

Example: choose 0.4 m^3^/s (14 cfs).

3.  Using a plot of the inflow hydrograph, draw an estimated outflow
    hydrograph (based on the target pumping rate) from a tangent on the
    lower portion of rising limb to the falling limb at a flow equal to
    the target total pumping rate.

Example: refer to Figure 6‑3.

4.  The area between the estimated pumping rate line and hydrograph
    represents the estimated required volume (*V~req~*).

Example: In Figure 6‑3, the volume is estimated to be 260 m^3^. This is
determined by breaking up the area into approximate right triangles and
calculating the area of the triangles.

> ![](media/image29.wmf){width="5.406944444444444in"
> height="3.6909722222222223in"}

26. []{#__RefHeading___Toc509049944 .anchor}Figure 6‑28. Estimate of
    storage required

## Collection System

A collection system conveys stormwater runoff from the highway to the
pumping station. A typical collection system includes some combination
of the following elements:

-   ditches,

-   roadway gutters,

-   inlets,

-   access holes,

-   channels,

-   conduits, and

-   trash gates or racks.

For detailed discussion on planning and design of these elements refer
to publications such as Hydraulic Engineering Circular No. 22, Urban
Drainage Design manual,^10^ and Hydraulic Design Series No. 4,
Introduction to Highway Hydraulics.^11^

Generally, the roadway gutters, while part of the collection system, are
not available for consideration as storage volume because they are
higher than the allowable high water, by definition. Only those elements
that provide volume between the maximum high water elevation and the
higher of the sump system inlet flow line elevation and the lowest
pumping elevation will affect the design of the pump system.

Elements of the collection system should be laid out to alignments,
elevations and slopes to suit the highway. No matter which design
philosophy prevails (See Section 6.3.2 - Storage Design Philosophies),
the maximum storage capacity can be achieved by keeping as much of the
collection system with a flow line elevation as close to the sump inlet
elevation as possible. The flow line of the collection system should be
kept as high as possible to minimize the depth of the wet well inlet
invert. However, the collection system must maintain a steep enough
slope to reduce the potential for sedimentation.

### Procedure to Establish Collection System

1.  If not already done, design the collection system in accordance with
    the standard storm drain design principles and the pertinent
    considerations and criteria that appear in Chapter 7. Refer to the
    FHWA publication, *Urban Drainage Design Manual,* HEC-22,^10^ for
    guidance on storm drain design.

2.  Prepare a simple layout and profile of the proposed collection
    system, including the storage unit if applicable, with annotation
    that includes:

-   conduit section dimensions,

-   conduit lengths,

-   conduit invert elevations at nodes, and

-   inlet invert and edge of pavement elevations at inlet openings.

## Maximum Highwater Elevation

The maximum highwater in the sump is the elevation that does not cause
the hydraulic grade line for the design event in the collection system
to exceed the allowable high water at the roadway low point.

### Roadway Low Point 

An allowable high water should be set some depth below the throat of the
lowest inlet in the collection system. The throat of the inlet refers to
the point in the inlet opening that controls the flow entering the
inlet. Usually, the lowest inlet will be at the sag point of the
roadway. Preferably, the depth of the allowable highwater below the
throat of inlet should be 0.6 m (2 ft) or more to provide a safety
margin. However, in flat terrain, in may not be practicable to attain
such a safety margin.

### Hydraulic Grade Line

The hydraulic grade line should be computed based on the design peak
inflow rates through the collection system. Refer to the FHWA
publication *Urban Drainage Design Manual, HEC-22*,^10^ for the
procedure.

### Procedure to Determine Allowable Highwater in Wet Well

1.  Establish the maximum allowable highwater at the roadway low point
    (HW~R(max)~) as the roadway elevation at the lowest inlet opening
    less a safety factor of 0.3 m -- 0.6 m (1 ft -- 2 ft).

2.  Compute the hydraulic grade line from the wet well to the lowest
    inlet in the roadway using the following:

-   annotated layout and profile of the collection system and wet well,

-   computed design peak inflow rates,

-   trial water level in wet well. The first trial level should be below
    the maximum allowable highwater at the roadway low point
    (HW~R(max)~) but above the soffit of the wet well inlet conduit, and

-   procedures presented in the FHWA publication, *Urban Drainage Design
    Manual*.^10^

3.  Compare the hydraulic grade line (HGL) at the lowpoint of the
    roadway with the maximum allowable highwater at the roadway low
    point (HW~R(max)~). Use the following decision table:

  ----------------------- ----------------------- -----------------------
  If HGL is:              Then:                   Comment

  Higher than HW~R(max)~  Repeat Step 2 using a   The trial level exceeds
                          lower trial water level allowable level
                          in wet well.            

  More than 75 mm (3 in.) Repeat Step 2 using a   The trial level is too
  lower than HW~R(max)~   higher trial water      low
                          level in wet well.      

  At or just below        Proceed to Step 4.      The trial level
  HW~R(max)~                                      represents HW~s(max)~.
  ----------------------- ----------------------- -----------------------

4.  Compare the resulting HW~s(max)~ to the soffit elevation of the
    storage unit at the intake. If HW~s(max)~ is below the soffit, then
    the storage unit will not be completely full. The options for
    proceeding are:

-   Reduce the flowline of the collection system, adjust the profile
    plot and annotation, and return to Step 1. Note that this will
    result in larger pump power requirements.

-   Reduce the height of the conduit system components and increase the
    width or number of barrels to maintain design capacities. Adjust the
    profile plot and annotation, and return to Step 1.

-   Proceed without adjusting the storage system. This is not preferred
    because of wasted volume.

## Wet Well System

From a hydraulic design perspective, consideration of the wet well at
this stage is limited to the contribution of volume to the total
available volume and the available volume at increasing water levels. A
local or preferred standard dimension and shape is usually chosen and
used for initial storage calculations or the storage in the wet well is
ignored for the trial design. The final dimensions of the sump are
established after specific pumps have been selected. Refer to Section
9.1 - Sump Size and Clearance Criteria for sump dimension criteria.

### Procedure to Select Preliminary Wet Well Dimensions

Minimum pump pit dimensions depend on the number, size and type of pump,
but the pump size depends on the storage provided, a part of which is
provided by the wet well size. In some cases, the wet well may provide
significant storage, and other case may provide only nominal storage.
Here, the overall wet pit dimensions are chosen as a first estimate.
Detailed sump size and clearance checks are performed after pump sizing
and selection.

1.  Choose a trial wet well size. Wet well sizes and shapes will vary
    according to highway agency preferences and type of station. For
    typical well types, refer to Section 3. - Pumps and Pump Station
    Types. At this stage, only the overall internal dimensions and shape
    are necessary.

```{=html}
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```
2.  Establish the lowest pumping elevation. For some typical details,
    this will be the wet well inlet invert elevation. For others, the
    lowest pumping elevation will be some preset depth below the wet
    well inlet invert elevation depending on the wet well details.

3.  Add the wet well and dimensions to the collection system layout and
    profile. The bottom elevation of the sump is not needed at this
    stage.

## Storage Unit

A storage unit is provided to achieve a desired storage volume in excess
of the storage provided by the collection system. A storage unit is an
integral component of the dry-pit station, where it also serves as the
wet well. It is not required for a wet-pit station; however, it is often
used to achieve a desired storage volume when the designer wishes to
reduce the required pump capacity. The storage unit can also serve as a
fire protection unit and as a sand trap.

The storage unit can be made of various materials and shapes, but
concrete boxes have been predominant. A typical storage unit is
illustrated in Figure 6‑4.

![](media/image30.png){width="6.499305555555556in"
height="3.2618055555555556in"}

27. []{#__RefHeading___Toc509049945 .anchor}Figure 6‑29. Typical storage
    unit

To minimize right-of-way requirements, single or multiple boxes or pipes
are placed parallel to the highway or transversely under the highway at
the low point of the collection system and depressed area. The boxes are
sized to store as much of the peak flow volume from the design storm as
is economically feasible. The storage unit may be designed to
accommodate temporary power outages or pump failures; however, the
provision of backup power and redundancy in the pumping capacity is
preferred.

A minimum storage volume can be established that will allow a hazardous
highway spill to be contained in the storage unit and its sand trap
until pumped out. In the event of a spill, the pump station would not be
contaminated or damaged.

The storage unit should have adequate access to allow for inspection and
maintenance. A frequent maintenance item will be the need to remove
sediment deposits and trash, so the type of access should be compatible
with the anticipated clean out method. For single barrel systems, access
hole spacing should conform to state policy. For multi-barrel systems,
access to each barrel should be provided either by individual access
holes or by horizontal access windows between the barrel walls.

## Storage Calculations

Table 6‑1 provides some quick reference equations for common sections
used in wet wells and collection systems.

The variables are defined below:

*d* = deepest depth in element, m (ft)

*s* = slope of element, m/m (ft/ft)

*s~s~* = side slope (ratio of vertical to horizontal), m/m (ft/ft)

*D* = diameter or rise, m (ft)

*B* = breadth (horizontal plane), m (ft)

*L* = length of element, m (ft)

*W* = width of element, m (ft)

*V* = volume of element, m^3^ (ft^3^)

The FHWA software program HY-22^16^can be used in conjunction with
HEC-22^10^ to compute storage volumes.

28. []{#__RefHeading___Toc509049850 .anchor}Table 6‑2. Storage
    properties of shapes

+--------+----------------------------------+-------------+-----------+
| **S    | **Area, *A***                    | **Wetted    | **Volume, |
| hape** |                                  | Perimeter** | *V***     |
|        | **m^2^ (ft^2^)**                 |             |           |
|        |                                  | **m (ft)**  | **m^3^    |
|        |                                  |             | (ft^3^)** |
+--------+----------------------------------+-------------+-----------+
| Rect.  | $\text{BW}$(plan area)           | n/a         | $$\t      |
|        |                                  |             | ext{Ad}$$ |
| (      |                                  |             |           |
| vert.) |                                  |             |           |
+--------+----------------------------------+-------------+-----------+
| Circ.  | $\frac{{\pi D}^{2}}{4}$ (plan    | n/a         | $$\t      |
| (      | area)                            |             | ext{Ad}$$ |
| vert.) |                                  |             |           |
+--------+----------------------------------+-------------+-----------+
| T      | $$d\lef                          | $$W         | $$\t      |
| rapez. | t( \frac{d}{s_{s}} + W \right)$$ |  + 2\sqrt{d | ext{AL}$$ |
| (h     |                                  | ^{2} + \lef |           |
| oriz.) |                                  | t( \frac{d} |           |
|        |                                  | {s_{s}} \ri |           |
|        |                                  | ght)^{2}}$$ |           |
+--------+----------------------------------+-------------+-----------+
| S      | $$\frac{D^                       | $$D\te      | $$\t      |
| egment | {2}}{8}\left\lbrack 2\text{cos}^ | xt{cos}^{-  | ext{AL}$$ |
| of     | {- 1}\left( 1 - \frac{2d}{D} \ri | 1}(1 - \fra |           |
| Circle | ght) - \text{sin}\left( 2\text{c | c{2d}{D})$$ |           |
|        | os}^{- 1}\left( 1 - \frac{2d}{D} |             |           |
|        |  \right) \right) \right\rbrack$$ |             |           |
+--------+----------------------------------+-------------+-----------+
| Rect.  | $$\text{dW}$$                    | n/a         | $$0\t     |
| Wedge  |                                  |             | ext{.}5\t |
|        |                                  |             | ext{AL}$$ |
+--------+----------------------------------+-------------+-----------+
| T      | $$d\lef                          | n/a         | $$        |
| rapez. | t( \frac{d}{s_{s}} + W \right)$$ |             | \frac{\te |
| Wedge  |                                  |             | xt{WsL}^{ |
|        |                                  |             | 2}}{2} +  |
|        |                                  |             | \frac{s^{ |
|        |                                  |             | 2}L^{3}}{ |
|        |                                  |             | 3s_{s}}$$ |
+--------+----------------------------------+-------------+-----------+
| Circ.  | End area, A, per segment of      | n/a         | $$L       |
| Wedge  | circle                           |             | \frac{23a |
| (U     |                                  |             | ^{3} + \t |
| ngula) |                                  |             | ext{cA}}{ |
|        |                                  |             | \frac{D}{ |
|        |                                  |             | 2} + c}$$ |
|        |                                  |             |           |
|        |                                  |             | where:    |
|        |                                  |             |           |
|        |                                  |             | $$c =     |
|        |                                  |             |  d - \fra |
|        |                                  |             | c{D}{2}$$ |
|        |                                  |             |           |
|        |                                  |             | $$        |
|        |                                  |             | a = \sqrt |
|        |                                  |             | {\frac{D^ |
|        |                                  |             | {2}}{4} - |
|        |                                  |             |  c^{2}}$$ |
+--------+----------------------------------+-------------+-----------+

### Sloping Conduit

The volume contained in a sloping conduit below a given water surface is
not represented by the volume of a prism, but a wedge. Table 6‑1
presents equations for wedges of rectangular and trapezoidal sections.
In a circular cross section, the shape is referred to as ungula.

#### Ungula Formula

Table 6‑1 includes an equation for the ungula volume. Variables are
identified in Figure 6‑5. The end area, A, is computed using the
equation provided in Table 6‑1 for a segment of a circle.

![](media/image31.png){width="5.5125in" height="2.6666666666666665in"}

29. []{#__RefHeading___Toc509049946 .anchor}Figure 6‑30. Ungula
    dimensions

### Example of Storage in a Sloping Pipe

A 160 m (525 ft) long reinforced concrete pipe with a diameter of 1.2 m
(3.9 ft) is placed at a slope of 0.004 m/m (0.004 ft/ft) and a
downstream flow line elevation of 20.0 m (65.62 ft). Calculate the
volume of water stored in the pipe at a depth of 0.5 m (1.64 ft).

Referring to Figure 6‑5 and Table 6‑1, the cross-sectional area at the
downstream end of pipe is as follows.

Using the equation for the segment of a circle,
$A = \frac{D^{2}}{8}\left\lbrack 2\text{cos}^{- 1}\left( 1 - \frac{2d}{D} \right) - \text{sin}\left( 2\text{cos}^{- 1}\left( 1 - \frac{2d}{D} \right) \right) \right\rbrack$$A = \frac{1\text{.}2^{2}}{8}\left\lbrack 2 \times \text{cos}^{- 1}\left( 1 - \frac{2 \times 0\text{.}5}{1\text{.}2} \right) - \text{sin}\left( 2 \times \text{cos}^{- 1}\left( 1 - \frac{2 \times 0\text{.}5}{1\text{.}2} \right) \right) \right\rbrack$
= 0.446 m^2^ (4.8 ft^2^)

Referring to Section A-A in Figure 6‑5,

$c = d - \frac{D}{2}$

$c = 0\text{.}5 - 1\text{.}\frac{2}{2}$ = (-)0.1 m (-0.33 ft)

$$a = \sqrt{\frac{D^{2}}{4} - c^{2}}$$

$a = \sqrt{\frac{1\text{.}2^{2}}{4} - ( - 0\text{.}1)^{2}}$ = 0.592 m
(1.94 ft)

Referring to Figure 6‑5, the horizontal length of pipe inundated by
water, *L*, is calculated as follows:

*L* = depth of flow/pipe slope

*L* = 0.5/0.004 = 125 m (410 ft)

Using the equation for the volume of an ungula,

$$V = L\frac{23a^{3} + \text{cA}}{\frac{D}{2} + c}$$

$V = \text{125} \times \frac{23 \times 0\text{.}\text{592}^{3} + ( - 0\text{.}1) \times 0\text{.}\text{446}}{1\text{.}\frac{2}{2} + ( - 0\text{.}1)}$
= 23.36 m^3^ (825 ft^3^)

### Procedure to Establish Storage Unit Dimensions

Since the total storage is the sum of all storage in the collection
system, storage unit and wet well below the maximum highwater and above
the lowest pump elevation, it is necessary to size the unit to ensure
that the total storage meets or exceeds the storage volume required.

1.  Establish a flow line profile from the collection system to the sump
    that will be used for the storage unit.

2.  Assuming the lowest pump elevation will be set at the invert of the
    storage unit at the sump entrance, compute the volume in the
    collection system (*V~cs~*) below the allowable highwater.

Example: the collection system storage is ignored as being
insignificant.

3.  Assume a standard sump shape and size. Compute the sump volume
    between the maximum highwater and lowest pumping elevation (*V~w~*).

Example: using a circular wet well with an inside diameter of 6.4 m (21
ft) and a maximum allowable highwater of 22 m (72.18 ft) and lowest
pumping elevation of 20 m (65.62 ft) the volume in the sump is:

*V~w~* = π x 0.25 x 6.4^2^ x (22 -- 20) = 64.3 m^3^ (2271 ft^3^)

4.  Choose a standard storage unit shape and section dimensions. Check
    local preferences and availability.

5.  Compute the cross-section area of the chosen conduit, *A~S~*.

Example: using a 1200 mm pipe, the cross-sectional area is:

*A~s~* = π x 0.25 x 1.2^2^ = 1.13 m^2^ (12.2 ft^2^)

6.  Compute the length of storage unit required, *L~S~* as:

$L_{s(\text{req})} = \frac{V_{\text{req}} - V_{\text{cs}} - V_{w}}{A_{s}}$
(6-1)

1.  

*A~S~* = Cross-section area of conduit, m^2^ (ft^2^)

*V~req~* = Minimum storage volume required, m^3^ (ft^3^)

*V~cs~* = Volume in collection system below allowable highwater, m^3^
(ft^3^)

*V~w~* = Volume in wet well below allowable highwater, m^3^ (ft^3^)

*L~s(req)~* ~=~ Total length of storage unit required, m (ft)

> For example, using the calculations above and an estimated required
> total volume of 260 m^3^ (9182 ft^3^), the estimated required length
> is:
>
> *L~s~* = (260 -- 0 -- 64.3) / 1.13 = 173 m (568 ft)

7.  Determine the number of barrels of conduit required by dividing the
    total length required, L~S(req)~, by the length available to fit the
    storage unit. For example, the longest storage unit length is 160 m:

> number of barrels required = 173 / 160 = 1.08

Since the required storage is only estimated try only 1 barrel.
Subsequent analysis will establish if the storage is sufficient.

### Procedure to Develop Stage-Storage Curve

The stage-storage curve represents the total storage that is available
within the system at any stage between the inlet elevation (invert) of
the pump station and the maximum allowable elevation in the wet well,
HW~s(max)~. The total storage includes storage in the collection system,
storage unit, and the wet well. The designer should compute storage
values from the lowest pump stop elevation to the maximum allowable
elevation. A level higher than the allowable is appropriate for
evaluating the check storm.

The following steps indicate how to develop a stage-storage
relationship.

Note: Some designers prefer to work in terms of actual elevation rather
than stage.

1.  Using the system profile plot, identify the lowest pumping elevation
    and set to zero stage. The available storage at this stage will be
    zero.

```{=html}
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```
2.  Choose an increment in stage.

Example: try 0.1 m (0.33 ft)

3.  Establish a table of stage and storage for the full range of stages
    using the chosen increment.

Example: see Table 6‑2.

4.  For each stage, compute the storage as the sum of storage volumes in
    each element of the storage system at that stage. This is where the
    profile plot and layout are useful, especially for extensive storage
    networks. Record the computed storage for each stage in the
    aforementioned table.

Example: at a stage of 0.5 m, the volume in the wet well is:

*V~w~* = π x 0.25 x 6.4^2^ x 0.5 = 16.08 m^3^ (568 ft^3^)

The volume in the collection system is assumed to be negligible

The volume in the storage unit is (see Section 6.8.2 - Example of
Storage in a Sloping Pipe for calculation):

*V~w~* = 23.36 m^3^ (826 ft^3^)

The total volume at 0.5 m stage is:

*V~t~* = 16.08 + 23.36 = 39.44 m^3^ (1393 ft^3^)

5.  Plot a curve of stage versus storage. The plot is especially useful
    in helping identify errors in the volume computations. The storage
    should increase with stage until HW~s(max)~ is reached.

Figure 6‑6 shows a completed stage versus storage curve using the value
from Table 6‑2.

30. []{#__RefHeading___Toc509049851 .anchor}Table 6‑3. Example stage
    storage table

![](media/image32.wmf){width="2.8131944444444446in"
height="5.270138888888889in"}

![](media/image33.wmf){width="6.031944444444444in"
height="4.141666666666667in"}

31. []{#__RefHeading___Toc509049947 .anchor}Figure 6‑31: Example stage
    versus storage curve

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#  {#section-3 .unnumbered}

# PUMP CONFIGURATION AND MASS CURVE ROUTING

## Introduction

This chapter discusses considerations, criteria, and procedures for:

-   pump configurations,

-   discharge line components,

-   total dynamic head,

-   system curves, and

-   mass curve routing.

## Criteria and Considerations for Pump Configurations

### Number of Pumps

The following table provides some quick-reference criteria for number of
pumps.

32. []{#__RefHeading___Toc509049852 .anchor}Table 7‑4. Suggested
    criteria for number of pumps

  ---------------------------------------- ------------------------------
  Criterion                                Number of Pumps

  Required Minimum                         2

  Preferred Minimum                        3

  Maximum                                  Not Specified
  ---------------------------------------- ------------------------------

### Size of Pumps

Generally, each main pump should have equal capacity and be of like
type. Alternatively, it may be desirable to provide a low flow pump,
sometimes termed nuisance pump, as the first to switch on. The remaining
pumps would have a larger capacity. During low runoff events, only the
small pump would be required, thus saving energy and reducing wear and
tear. This is especially desirable when high total pumping capacity is
provided by a few large pumps. The low flow pump may be turned off
during peak flow events and is never included in the alternating start
arrangement for the larger pumps.

### Pump Sequencing

There are no specific criteria for pump sequencing. The number of
sequencing alternatives is a function of the number of pumps; however,
some general recommendations are appropriate.

-   Use a low capacity pump as the first to switch on when using a small
    number of large capacity pumps. This pump is not part of the
    sequencing that follows.

-   Provide automatically alternating sequences to distribute use of the
    larger pumps. This approach involves assigning a starting order for
    the pumps (say 1, 2, 3), then after one complete sequence the
    starting order is rearranged for the next operation (say 3, 1, 2),
    and so on. Otherwise, the first pump is always the most used and
    would require more frequent maintenance and repair than the others.
    Also, this has the effect of increasing cycling time for a given
    storage volume or reducing the storage requirement for a given
    cycling time.

-   The traditional sequence uses a cut-off order that is the reverse of
    the switch-on order. In this way, the first pump on is the last pump
    off.

The table below provides some sample starting sequences for systems with
2 to 4 pumps, the trend is clear for additional pumps.

  ----------- ----------- ----------- ----------- ----------- -----------
  No. of      First       Second      Third       Fourth      Fifth
  Pumps       Sequence                                        

  2           1-2         2-1         1-2         2-1         1-2

  3           1-2-3       3-1-2       2-3-1       1-2-3       3-1-2

  4           1-2-3-4     4-1-2-3     3-4-1-2     2-3-4-1     1-2-3-4
  ----------- ----------- ----------- ----------- ----------- -----------

The above sequencing is likely to provide the longest cycling times.

### Pump Switching Elevations

The pump switching elevations should be set to ensure that the minimum
cycling time will be greater than that specified by the manufacturer for
a pump type and size. Refer to Section 7.2.9 - Pump Cycling Time for
volume required to achieve minimum cycling time.

It is necessary to first establish the stop elevations for each pump in
the station. Generally, unless specific configuration details dictate
otherwise, the lowest pump stop elevation should be set at the invert
elevation of the storage unit at the entrance to the sump. (If it is set
higher, some of the storage unit will not be used during pumping.)
Subsequent stop elevations can either be set at the same elevation as
the lowest pump or more preferably staggered at predetermined heights
above the previous pump stop level. Sometimes the height difference may
be based on the sensitivity of the sensors used for switching (See
Section 11.6.3 - Water Level Sensors).

Trial start elevations are established by determining the elevations at
which the volume difference between the start and stop elevations for
the particular pump is equal to the minimum cycle volume computed using
Equation 7-6.

### Procedure to Estimate Capacity and Number of Pumps

Use the following decision table to determine how to establish a
configuration.

  ----------------------------- ----------------- -----------------------
  If the design is based on:    Then use          After which:
                                alternate:        

  Fixed peak outflow, Q~P(req)~ A                 Proceed to usable
                                                  storage and mass curve
                                                  routing.

  Fixed storage                 B                 Proceed to usable
                                                  storage and mass curve
                                                  routing.

  Optimal pump capacity/storage B                 Proceed to usable
                                                  storage and mass curve
                                                  routing, but multiple
                                                  iterations will be
                                                  necessary.
  ----------------------------- ----------------- -----------------------

#### Alternate A

For the trial storage system determined in Chapter 6. - Storage System,
perform the following:

1.  Compute the required total pumping in consistent units -- m^3^/hour
    or gpm.

```{=html}
<!-- -->
```
7.  Select a trial number of pumps. Refer to Table 7‑1.

8.  Calculate the required capacity of each pump. The recommended design
    is to divide the total pumping rate by the number of pumps to
    establish equally sized pumps. For large pumps, a low flow pump may
    be necessary, but the main pumps should still be equally sized to
    handle 100% of the design flow.

#### Alternate B

For the trial storage system determined in Chapter 6. - Storage System,
perform the following:

1.  Plot the inflow hydrograph.

```{=html}
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```
9.  Referring to Figure 7‑1, use the tangent on the rising limb of the
    inflow hydrograph to draw a line to a randomly selected point on the
    receding limb.

10. Estimate the volume contained between the line established in Step 2
    and the top portion of the inflow hydrograph.

11. If the estimated volume is approximately equal to the total
    available storage provided, read the discharge rate at which the
    line intersects the receding limb. This is the target pump rate for
    the trial (or established) storage configuration. If the estimated
    volume is not approximately equal to the total available storage
    provided, return to Step 2.

![](media/image34.wmf){width="5.225694444444445in"
height="3.4652777777777777in"}

33. []{#__RefHeading___Toc509049948 .anchor}Figure 7‑32. Estimating
    total pumping rate

### Pump Cycling

Cycling refers to the time between starts of an individual pump. The
shorter the cycling time, the more frequent a pump must start and stop.
Each start of the pump requires a power surge. The power requirements
increase with pump size. Also, the friction and vibration associated
with starting the pump induces heat and wear. Repeated starting and
stopping can result in overheating and excessive wear on the pump
components. Therefore, it is necessary to keep cycle times as long as
practicable.

Cycling is a function of storage and the pump discharge rate. For a
given volume of storage, the cycling time reduces with increasing
pumping rate. For a given pumping rate, the cycling time increases with
increasing storage. For stormwater pumps, actual cycling times will vary
in response to a particular runoff event. The characteristics of a
runoff hydrograph will vary from one event to the next.

### Allowable Minimum Cycling Time

The allowable minimum cycling time is dependent on the specific
characteristics of the pump. Manufacturers provide specifications for
the maximum number of starts per hour which translates to a minimum
cycling time for individual pumps. For example, 10 starts per hour, or
6-minute cycles, may be quoted for a submersible pump. Generally,
minimum cycling time increases with increasing pump capacity. Also,
minimum cycling times vary with pump type: typically, minimum times for
vertical motor-driven pumps are higher than for submersible pumps of
similar capacity.

### Usable Storage

There is a distinction between the volume of storage that is available
for detaining the inflow hydrograph and the volume that is usable for
pump cycling. See Section 6.3.3 - Available Storage. A lesser volume
than the available storage is usable for cycling times because at any
given moment as a pump turns on, some of the volume in the storage
system is already occupied by water that is being conveyed to the pump.
Under the assumption that the inflow rate has not changed when the pump
turns off then on again, the same volume is still being used to convey
water to the pump. Only the volume above this conveyance level is usable
during pump cycling. Usable volume is a function of:

-   sump dimensions,

-   pump start elevation,

-   pump stop elevation,

-   storage system dimensions, and

-   depth of flow in the storage system.

All unobstructed volume in the sump between a pump's start and stop
elevations contributes to the usable volume. The volume increases as the
difference between start and stop (pump range) increases. As the width
of the storage system increases, the depth used to convey flow to the
pump decreases and the usable volume increases.

### Pump Cycling Time

#### First Pump

The following provides proof that, for a given pump with a capacity,
Q~p~, the cycling time will be a minimum when the inflow, Q~i~, is equal
to half of the pump capacity.

Assumptions:

-   When pumping, the pump rate is constant and at pump capacity, *Q~p~*

-   The worst condition considered is a constant inflow rate, *Q~i~*

-   No pumping during filling cycle

The time to empty storage volume, *V*, is:

$t = \frac{V}{Q_{p} - Q_{i}}$ (7-1)

The time to fill the storage system (no pumping) is:

$t = \frac{V}{Q_{i}}$ (7-2)

If *Q~i~* is expressed as a multiple of *Q~p~*, *Q~i~ = xQ~p~*, then the
total cycle time is:

$t = \frac{V}{Q_{p} - \text{xQ}_{p}} + \frac{V}{\text{xQ}_{p}}$ (7-3)

For the minimum value of *t*,

$$\frac{\text{dt}}{\text{dx}} = - \frac{\text{VQ}_{p}}{\left( Q_{p} - \text{xQ}_{p} \right)^{2}} - \frac{V}{x^{2}Q_{p}} = 0$$

Rearranging and dividing by *V* gives:

$$Q_{p^{2}}x^{2} + (Q_{p} - Q_{p}x)^{2} = 0$$

$$For which,

$$x = 0\text{.}5$$

Thus,

$Q_{i} = 0\text{.}5Q_{p}$

So, for the minimum cycle time, *t*, substituting for *Q~i~* in Equation
7-1 gives:

$t = \frac{4V}{Q_{p}}$ (7-4)

If time is in minutes and flow rate is in cubic meters per second (cfs),
the minimum cycle time is then described by Equation 7-5.

$t = \frac{V}{\text{15}Q_{p}}$ (7-5)

Equation 7-5 can be used as a gauge to check cycling time for the first
pump. However, since the inflow rate to a stormwater pump station is not
constant, it is possible that the time to fill the usable storage could
be shorter if the rainfall intensity and subsequent inflow rate
increases significantly after the pump has evacuated the storage pit. If
this occurs, the cycle time would be shorter than that established by
Equation 7-5. The hypothetical worst-case cycle time would occur if the
inflow stops just after the pump kicks in, and then immediately after
the pump has evacuated the storage pit the inflow begins again at an
inordinate rate such that the time to refill the pit is negligible. The
cycle time would then reduce to *t = V/*60*Q~p~*. Of course, this is
highly unlikely, but it demonstrates that Equation 7-5 is not a strict
minimum for a stormwater pump.

For design, it is usual to determine the required minimum volume for
cycling by rearranging Equation 7-5 and by setting *t* to the
manufacturer's recommended minimum cycle time:

$V_{\text{min}} = \text{15}Q_{p}t$ (7-6)

2.  

*Q~p~* = individual pump rate, m^3^/s (cfs)

*t* = minimum cycle time, mins

*V~min~* = minimum required cycle volume, m^3^ (ft^3^)

#### Cycling for Subsequent Pumps

The complexity of cycling checks can increase with the number of pumps.
It is often assumed that if cycling criteria for the first pump are met,
the subsequent pumps will have at least the same or longer cycling
times. However, it can be shown that Equation 7-6 is valid for any
number of equal-sized pumps when each volume, V~n~ is set equal to
*V*~min~, and is applied between the start and stop elevations of each
pump as indicated in Figure 7‑2. The proof is similar to that for one
pump and is summarized as follows.

For the n^th^ pump,

nQ~p~ \> Q~i~ \> (n-1)Q~p~

Where:

n = number of pumps in the station,

Q~p~ = pumping rate of each individual pump,

Q~i~ = a worst-case constant inflow rate for the particular pump cycle,
and

V~n~ = cycle volume for n^th^ pump (volume between start and stop of
n^th^ pump)

![](media/image35.wmf){width="4.282638888888889in"
height="2.390277777777778in"}

34. []{#__RefHeading___Toc509049949 .anchor}Figure 7‑33. Cycling volumes

The cycle time for the n^th^ pump is:

$t = \frac{V}{\text{nQ}_{p} - \text{xQ}_{p}} + \frac{V}{\text{xQ}_{p} - (n - 1)Q_{p}}$
(7-7)

or:

$$t = \frac{V}{Q_{p}(n - x)} + \frac{V}{Q_{p}(x - n + 1)}$$

Note that this is the time to fill and empty only the volume between the
n^th^ pump start and stop elevations, thus, once the n^th^ pump stops,
n-1 pumps are still operating.

For the minimum value of *t*,

$$\frac{\text{dt}}{\text{dx}} = \frac{V_{n}}{Q_{p}(n - x)^{2}} - \frac{V_{n}}{Q_{p}(x - n + 1)^{2}} = 0$$

Rearranging and multiplying by *Q~p~*/*V* gives:

$$(x - n + 1)^{2} - (n - x)^{2} = 0$$

which reduces to:

$$2x - 2n + 1 = 0$$

or:

$$x = n - 0\text{.}5$$

Thus, the cycling time is a minimum for the second pump when the inflow
rate is 1.5 times the individual pump rate, 2.5 times the individual
pump rate for the third pump, and so on as summarized below.

35. []{#__RefHeading___Toc509049853 .anchor}Table 7‑5. Critical inflow
    rates for pump cycling

  ----------------------------- -----------------------------------------
  **Pump Number**               **Critical inflow rate**

  1                             0.5Q~p~

  2                             1.5Q~p~

  3                             2.5Q~p~

  4                             3.5Q~p~
  ----------------------------- -----------------------------------------

Substituting for x in Equation 7-7:

$$t = \frac{V}{Q_{p}(n - (n - 0\text{.}5))} + \frac{V}{Q_{p}((n - 0\text{.}5) - n + 1)}$$

which reduces to:

$t = \frac{4V_{n}}{Q_{p}}$ (t in seconds)

or:

$t = \frac{V_{n}}{\text{15}Q_{p}}$(t in minutes)

This rearranges to:

$$V_{n} = \text{15}Q_{p}t$$

Thus, for any given number of pumps, the usable volume between the start
and stop elevations for the pump in question must meet or exceed the
value established in Equation 7-6.

### Usable Storage Calculations

The usable storage for pump cycling is between the start and stop
elevations of the pump under consideration less the volume below uniform
depth (but above the stop elevation) in the collection system and
storage system. The assumption here is that the inflow rate maintains
uniform depth, d~u~, in the collection line and storage unit after the
pump shuts off, thus the volume between uniform depth and the flowline
of the collection system and storage unit is unavailable. (See Figure
7‑3). This is often assumed no matter what the configuration of the
storage unit. The flow used for uniform depth is the critical flow for
the particular pump as identified in Table 7‑2.

![](media/image36.wmf){width="5.229861111111111in"
height="2.9916666666666667in"}

36. []{#__RefHeading___Toc509049950 .anchor}Figure 7‑34. Usable storage
    at any stage

The volume equations shown in Section 6.8 - Storage Calculations apply
when determining usable storage. However, it is essential that the
appropriate portions of the wet well, storage unit and collection system
are used. For any given reach of conduit, the usable portion is the
volume in the conduit that is enclosed by the water level and the
uniform depth line. The uniform depth in a conduit may be determined as
follows:

1.  Determine the critical discharge, Q, for the number of pump in
    question by referring to Table 7‑2.

2.  Choose a trial depth d~(trial)~.

3.  Compute the discharge, Q~u~, for the trial depth using a form of
    Manning's Equation:

$Q_{u} = \frac{C}{n}\text{AR}^{\frac{2}{3}}S^{\frac{1}{2}}$ (7-8)

where:

*Q~u~* = discharge, m^3^/s (cfs)

*C* = unit coefficient = 1 for SI (1.486 for English)

*n* = Manning's roughness coefficient

*A* = area of flow at uniform depth, m^2^ (ft^2^)

*R* = hydraulic radius = area/wetted perimeter, m (ft)

*S* = slope of conduit, m/m (ft/ft)

a.  Refer to HY-22^16^ for a computer program to compute uniform depth,
    or

b.  Use Table 6‑1 for the appropriate conduit shape to find equations
    for area and wetted perimeter.

```{=html}
<!-- -->
```
4.  Use the following table to decide how to proceed:

  ----------------------------------- -----------------------------------
  If:                                 Then:

  Q~u~ \> Q                           Decrease d~(trial)~ by using a
                                      value halfway between the current
                                      and previous values tried and
                                      return to Step 3

  Q~u~ \< Q                           Increase d~(trial)~ by using a
                                      value halfway between the current
                                      and previous values tried and
                                      return to Step 3

  Q~u~ = Q                            Proceed to Step 5
  ----------------------------------- -----------------------------------

5.  The current d~(trial)~ represents uniform depth, d~u~.

The volume under the uniform depth line may be computed as a prism of
length, L. The length is the lesser of the conduit length and the
distance between the downstream end of the conduit and the point at
which the water level intersects with uniform depth (Figure 7‑3). Refer
to Table 6‑1 for volumes of rectangular and trapezoidal sections and
circular segments.

#### Example of Uniform Depth Calculation

A 160 m (525 ft) long storage unit for a two-pump facility is to
comprise a 1.2 m (3.9 ft) reinforced concrete pipe at a slope of 0.004
m/m (0.004 ft/ft). The individual pump rate is 0.2 m^3^/s (7 cfs).
Consider the first pump.

1.  The discharge at which the potential cycle time will be at a minimum
    is half of the pump rate for pump number 1: *Q* = 0.2/2 = 0.1 m^3^/s
    (3.5 cfs).

2.  Choosing a trial depth of 0.6 m (2 ft):

3.  $Q_{u} = \frac{C}{n}\text{AR}^{\frac{2}{3}}S^{\frac{1}{2}} = \frac{1}{\text{.}\text{013}} \times 0\text{.}\text{565} \times (\frac{0\text{.}\text{565}}{1\text{.}\text{885}})^{\frac{2}{3}} \times 0\text{.}\text{004}^{\frac{1}{2}} = 1\text{.}2$
    m^3^/s (42.4 cfs)

4.  *Q~u~* \> *Q*, therefore, reduce the assumed depth. After several
    iterations, repeating Step 3 for d = 0.165 m (0.54 ft) gives:
    $Q_{u} = \frac{1}{\text{.}\text{013}} \times 0\text{.}\text{094} \times (\frac{0\text{.}\text{094}}{0\text{.}\text{913}})^{\frac{2}{3}} \times 0\text{.}\text{004}^{\frac{1}{2}} = 0\text{.}1$
    m^3^/s (3.5 cfs)

5.  Since, *Q~u~* = *Q*, uniform depth is 0.165 m (0.54 ft).

#### Stage versus Usable Storage

Using a similar approach to development of the stage-storage curve, the
usable storage can be calculated by taking the available volume at the
stage for the pump number under consideration and subtracting the volume
in the collection system and storage unit that is below uniform depth
for the critical flow rate (Table 7‑2). Table 7‑3 shows a usable storage
table for the storage system used in Section 6.8.4 - Procedure to
Develop Stage-Storage Curve. This approach is often precluded by
ensuring that the cycling volume is provided in the sump between the
start and stop levels for each pump.

37. []{#__RefHeading___Toc509049854 .anchor}Table 7‑6. Example usable
    storage table

![](media/image37.wmf){width="5.493055555555555in"
height="5.4430555555555555in"}

### Procedure to Determine Trial Switching

The switching scheme will affect the distribution of pumping with time.
The implications of poor switching include excessive cycling and
exceeding the allowable highwater level. The following approach
establishes a trial scheme that is subsequently checked for both
conditions.

1.  Establish the stop elevations (STOP) for all pumps. For the first
    pump, the stop elevation (Stop 1) should be set at the invert of the
    storage unit at wet well entrance or based on the typical wet well
    detail to be used. Suggested approaches for the subsequent stop
    elevations (Stop 2, Stop 3, etc) are either to stagger them at
    preset intervals of say 150 mm (0.5 ft) or 300 mm (1 ft), or to set
    all stops at the same level.

Example: Choosing 300 mm intervals, Stop 1 = 0 m (0 ft), Stop 2 = 0.3 m
(1 ft)

12. Determine the total volume at each stop elevation using the
    stage-storage curve.

Example: Referring to the example stage-storage curve established in
Section 6.8.4 - Procedure to Develop Stage-Storage Curve,

At Stop 1 = 0 m, the stop volume, S~o1~ = 0 m^3^ (0 ft^3^)

At Stop 2 = 0.3 m, the stop volume, S~o2~ = 16.45 m^3^ (581 ft^3^)

13. Estimate the minimum cycling time (*t~c~*) for the main pump
    (largest) using pump manufacturer's information based on the trial
    pump size. For large submersible pumps a value of 6 minutes is
    typical. For vertical pumps, a value of 10 minutes is typical.

Example: Assume 6 starts per hour (to allow either a vertical pump or a
submersible pump), which equates to a cycle time of 10 mins.

14. Compute the minimum required usable storage using Equation 7-6.

Example: For a pump capacity of 0.2 m^3^/s (7 cfs), the minimum cycling
volume for each pump is:

V~u(min)~ = 15 x 0.2 x 10 = 30 m^3^ (1059 ft^3^)

15. Establish a trial pumping range, δh, for the first main pump as
    follows:

```{=html}
<!-- -->
```
a.  Determine the elevation at which the minimum cycling volume (usable
    volume) is met or just exceeded using the stage-storage curve, or
    the Usage Storage Table, Start 1.

Example: Referring to Table 7‑3, the stage at which the usable storage
for 1 pump exceeds 30 m^3^ is 0.7 m (2.3 ft). This is Start 1.

b.  Calculate the trial range, δh, as the difference between Start 1 and
    Stop 1

Example: The trial range is 0.7 -- 0 = 0.7 m (2.3 ft)

c.  If δh is less than 150 mm (0.5 ft), use 150 mm (0.5 ft), reset Start
    1 to Start 1 + 150 mm (0.5 ft) and use the stage storage curve to
    determine the total storage at Start 1. A minimum difference of 150
    mm (0.5 ft) is suggested to reduce the potential for concurrent
    activation of two or more pumps as a result of waves or other
    fluctuations in the water level.

```{=html}
<!-- -->
```
16. Establish remaining pump start elevations (Start 2, Start 3, etc.)
    as follows. For each remaining pump:

```{=html}
<!-- -->
```
a.  Determine the usable volume at the stop elevation.

Example: Referring to Table 7‑3, the usable volume at Stop 2 = 0.3 m
(1ft) for two pumps operating is 9.65 m^3^ (341 ft^3^)

b.  Add the required cycling volume (V~u(min)~) to the usable volume at
    the stop elevation to find the usable volume required for starting.

Example: Start available volume for Pump 2, S~2~ = 30 + 9.65 = 39.65
m^3^ (1400 ft^3^)

c.  Determine the elevation at which the required starting usable volume
    is met or just exceeded using the stage versus usable storage curve
    for the current number of pumps in operation. Set this as the
    preliminary start elevation. Figure 7‑4 is a graphical
    representation of the relationship between usable volume and
    starting levels.

Example: Referring to Table 7‑3, the stage at which a usable volume of
39.65 m^3^ is exceeded is:

Start 2 = 0.7 m (2.3 ft)

d.  If the start elevation is less than a minimum desirable height above
    the stop elevation, use the minimum desirable increment. This
    accounts for possible fluctuations due to turbulence and sensitivity
    of the sensors. A value in the range of 150 mm to 300 mm is typical.

Example: Since Start 1 is at 0.7 m, set Start 2 to 0.7 + 0.3 = 1.0 m
(3.1 ft)

![](media/image38.wmf){width="3.938888888888889in"
height="2.720138888888889in"}

38. []{#__RefHeading___Toc509049951 .anchor}Figure 7‑35. Usable volume
    and pump start levels

```{=html}
<!-- -->
```
17. Develop a table of switching levels (on and off) and available
    storage volumes. You can retrieve the available storage volumes from
    each elevation from the stage-storage curve derived in Section
    6.8.4 - Procedure to Develop Stage-Storage Curve.

Example: The following table relates the trial switching levels and
available volumes from Table 6‑2.

39. []{#__RefHeading___Toc509049855 .anchor}Table 7‑7. Pump switching
    table

![](media/image39.wmf){width="4.413194444444445in"
height="0.9402777777777778in"}

18. Develop a stage-discharge curve based on the pump switching table.
    Figure 7‑5 shows a resulting plot for the switching table above and
    two pumps rated at 0.2 m^3^/s (7 cfs).

![](media/image40.wmf){width="6.497916666666667in"
height="4.4430555555555555in"}

40. []{#__RefHeading___Toc509049952 .anchor}Figure 7‑36. Sample
    stage-discharge curve

## Mass Curve Routing

The primary hydraulic evaluation of a trial pump station configuration
is the determination of the cumulative outflow using the design mass
inflow curve. The procedure to do this is called mass curve routing. The
objectives of mass curve routing are to:

1\. Determine the maximum available storage volume required by the trial
pump size and switching and compare it with the trial available storage
provided,

2\. Determine the number of cycles a pump will operate.

No matter what design philosphy is employed, the mass curve routing
cannot proceed until the following are established:

-   inflow mass curve (refer to Section 5.5 - Procedure to Determine
    Mass Inflow),

-   stage-storage curve (refer to Section 6.8.4 - Procedure to Develop
    Stage-Storage ), and

-   stage-discharge curve (refer to Section 7.2.11 - Procedure to
    Determine Trial Switching)

### Procedure to Perform Mass Curve Routing

Refer to Figure 7‑6 for the following steps which use the pumping
operation established in Table 7‑4 with two pumps rated at 0.2 m^3^/s (7
cfs).

1.  Plot the mass inflow curve (cumulative inflow versus time) on scaled
    paper. And set the storage to zero.

2.  Identify the time at which the volume reaches the start volume for
    the first pump (point A on Figure 7‑6). Draw a line at a slope that
    represents the pumping rate for one pump operating from this time at
    zero storage (a slope of 0.2 m^3^/s for this example). This line
    begins the outflow curve.

3.  If the pump rate line intersects the mass curve line, the pumping
    ceases. This is represented by drawing a horizontal line from the
    point of intersection. If the pump rate line does not intersect the
    mass curve line, jump to Step 5. For this example, you would need to
    jump to Step 5 because the mass inflow volume is increasing faster
    than the outflow.

4.  Continue the horizontal line until the volume difference between the
    mass curve and outflow curve exceeds the start volume for the first
    pump again.

5.  If the difference between the mass curve and outflow curve reaches
    the starting volume for the next pump (point B), draw a line that
    represents the discharge rate for an additional pump (0.4 m^3^/s (14
    cfs) for this example).

6.  At any point, if the volume difference drops to one of the pump stop
    volumes, the rate line is reduced to reflect the lower pump rate
    (for example, point C).

7.  If the outflow line reaches the mass curve line (point D), the rate
    line is reduced to zero (horizontal) and Steps 4 to 7 are repeated
    until the mass curve has ended.

8.  Establish the maximum volume in storage by drawing a line that is
    tangent to the mass inflow curve and parallel to the maximum pumping
    rate during the curve routing. The vertical difference between the
    tangent point and the outflow curve represents the maximum required
    storage volume. In the example in Figure 7‑6, the maximum storage
    volume is 223 m^3^ (7875 ft^3^). Note that, in the example shown in
    6.3.4 Procedure to Estimate Total Available Storage Required, the
    provisional estimate of volume required was 260 m^3^ (9182 ft^3^).

![](media/image41.wmf){width="6.240277777777778in"
height="4.295833333333333in"}

41. []{#__RefHeading___Toc509049953 .anchor}Figure 7‑37. Example of
    graphical method for mass curve routing

### Procedure to Check Routing Mass Curve

1.  Make note of the total storage volume provided, V~t~, and the
    maximum required volume in storage, V~(req)~, from the routing
    procedure.

2.  Review the mass curve routing to identify any periods in which more
    than one pump begins. If two pumps start within about 1 minute of
    each other, it will be preferable to adjust start elevations to
    increase the time between two pumps activating.

3.  Evaluate the number of times a pump must start and stop.

4.  Use the following table to decide how to proceed:

+-----------------------+-----------------------+-----------------------+
| Condition             | Likely cause          | Suggested action      |
+-----------------------+-----------------------+-----------------------+
| V ~(req)~ \> V~t~ but | -   Insufficient      | -   Increase storage, |
| cycle times long      |     storage, or       |     or                |
| enough                |                       |                       |
|                       | -   Pumping capacity  | -   Increase capacity |
|                       |     too low, or       |     or number of      |
|                       |                       |     pumps, or         |
|                       | -   Pumps not         |                       |
|                       |     operating soon    | -   Reduce switch-on/ |
|                       |     enough            |     switch-off        |
|                       |                       |     elevations        |
+-----------------------+-----------------------+-----------------------+
| V ~(req)~             | -   Pumping capacity  | -   Decrease capacity |
| significantly lower   |     too high          |     or number of      |
| than V~t~ but cycle   |                       |     pumps             |
| times adequate        |                       |                       |
+-----------------------+-----------------------+-----------------------+
| V ~(req)~ \< V~t~ but | -   Insufficient      | -   Adjust switching  |
| cycle times too short |     storage between   |     elevations to     |
|                       |     switching         |     increase storage  |
|                       |     elevations        |     difference for    |
|                       |                       |     most sensitive    |
|                       |                       |     pump, or          |
|                       |                       |                       |
|                       |                       | -   Increase storage  |
|                       |                       |     volume            |
+-----------------------+-----------------------+-----------------------+
| V ~(req)~ \< V~t~ and | Pumping scenario is   | Proceed to next stage |
| cycle times adequate  | satisfactory          |                       |
+-----------------------+-----------------------+-----------------------+

Example: Referring to Figure 7‑6 and Table 6‑2:

-   The maximum volume required is 223 m^3^ (7875 ft^3^).

-   The total available volume (at maximum highwater stage of 2.0 m (3.3
    ft) is 245 m^3^ (8652 ft^3^).

-   The shortest time between starting of two pumps is from point A to
    point B - about 16 minutes.

-   In a period of about 70 minutes (beginning at point A) Pump 1 cycles
    once for the design inflow.

# DISCHARGE LINE AND PUMP SELECTION

## Discharge Line Components

For pump station design, the discharge line begins at the discharge end
of the pump and ends at the beginning of the discharge conduit or
outfall. A discharge line may include some combination of the following
elements:

-   Pipe

-   Stop/check valves

-   Flap gates/valves

-   Elbows

-   Manifolds

-   Tee's

-   Reducers

-   Expanders

-   Brackets, bolts and other fixtures

### Basic Line

The discharge line should be kept as short and simple as possible. The
simplest configuration is where each pump has its own discharge line,
entirely independent of the other pumps. Each discharge line conveys
pumped water from the pump to a channel or conduit outside the pump
station. The elbow of the vertical riser from the pump should be set
higher than the discharge line, with a slope down to the discharge end
to minimize the volume of back flow when the pumps switch off. Where it
is practicable, the centerline of each discharge pipe should be placed
higher than the design backwater elevation in the receiving channel or
conduit. A flap gate is generally preferred and should be placed at the
terminus of each discharge line to prevent back flow if the centerline
elevation at the end of the discharge pipe is below the design backwater
elevation in the receiving structure. Consideration should also be given
to the potential for back flow resulting from storms in excess of the
design storm. A check valve may be desirable to prevent such back flow.

### Manifold System

When excessive length and cost makes individual discharge lines
impracticable, it is usual to connect the individual pump discharges
into a common discharge line large enough to direct the combined
discharge at an acceptable velocity. The connection element is called a
manifold. Each pump discharge line must include a check valve to prevent
recirculation of flow. It is rarely necessary to use a manifold system
in highway pump stations.

### Design Size

The size of the discharge pipe should be:

at least as large as the pump discharge diameter,

based on a suggested maximum discharge velocity of 3 m/s (10 fps), and

determined using the following equation:

$D = 1\text{.}\text{128}\sqrt{\frac{Q}{V}}$ (8-1)

3.  

*D* = pipe diameter, m (ft)

*Q* = discharge in pipe, m^3^/s (cfs)

*V* = maximum velocity, m/s (fps)

### Procedure to Determine Discharge Pipe Size

1.  Select a trial discharge line configuration. You will have an idea
    of pipe lengths required based on your pump location and proposed
    outfall. You will need to decide if you will use a manifold system
    or separate discharge lines and you will need to estimate the number
    of elbows, valves, and other appurtenances.

Example: Separate discharge lines are desired for two 0.2 m^3^/s (7 cfs)
pumps. Each line will need to be 20 m (66 ft) long with two 90 degree
elbows.

2.  Select a maximum discharge velocity, V~d~, say 3 m/s (10 fps), and
    compute the discharge pipe size using Equation 8-1:

Example: The target pipe diameter is:

D = 1.128 x (0.2 / 3)^0.5^ = 0.29 m (0.95 ft)

3.  Round the diameter up to the nearest standard size.

Example: The nearest standard diameter for the target pipe size is 300
mm (12 in.)

### Pump Discharge Pipe Material and Configuration Guidelines

Steel or ductile iron pipe are the primary choices for the pump
discharge line. In the absence of other information, the following table
provides guidance on pump discharge line configuration:

42. []{#__RefHeading___Toc509049856 .anchor}Table 8‑8. Suggested pipe
    material selection

+---------------------+---------------------+--------------------------+
| Line Length         | Suggested           | Recommended material     |
|                     | Configuration       |                          |
+---------------------+---------------------+--------------------------+
| \< 17m (50 ft)      | Individual line per | Steel or ductile iron    |
|                     | pump                |                          |
+---------------------+---------------------+--------------------------+
| 17 m -- 65 m (50 ft | Individual line per | Steel or ductile iron    |
| -- 200 ft)          | pump                | inside station to        |
|                     |                     | concrete, corrugated     |
|                     |                     | metal, or plastic        |
|                     |                     | conduit outside station  |
+---------------------+---------------------+--------------------------+
| \> 65 m (200 ft)    | Individual lines to | Steel or ductile iron    |
|                     | common conduit      | inside station to        |
|                     |                     | concrete, corrugated     |
|                     | or                  | metal, or plastic        |
|                     |                     | conduit conduit outside  |
|                     | Manifold to single  | station                  |
|                     | line                |                          |
|                     |                     | Steel or ductile iron    |
|                     |                     | manifold in side station |
|                     |                     | to concrete, corrugated  |
|                     |                     | metal, or plastic        |
|                     |                     | conduit outside station  |
+---------------------+---------------------+--------------------------+

#### Steel Pipe Grade

For typical stormwater pump stations, discharge heads are less than 20 m
( 50 ft). Associated pressures are relatively low so that a nominal 6 mm
(1/4 inch) thickness of steel pipe wall will suffice. However, the
stresses due to both internal pressure and external loading of backfill
need to be checked. Pipe of ASTM A53 quality is satisfactory, or where
fabrication is required, such as for a manifold, ASTM A36 steel is
normally used. Although on occasions, ASTM A 283 Grade C has been
specified for discharge lines and manifolds, it is not usually used if
any premium price is involved compared with A36.

#### Steel Pipe Coating

Steel pipe and accessories require galvanizing or epoxy lining and
coating as protection against corrosion, the former being preferable for
interior and exterior coating of lines up to about sixteen‑inch
diameter, whether exposed inside the station structure or buried
outside. Coal tar coating and pressure sensitive tape wrap are also used
to protect buried steel pipe. For larger lines, the coatings mentioned
are sometimes replaced by cement mortar, which is particularly
applicable to manifolds buried outside the station.

#### Steel Pipe Joints

Buried flanged joints in steel pipe are frequently a source of leaks or
internal corrosion in later years and should be avoided if possible by
fabricating the discharge lines in one piece, or making field welded
joints. Internal corrosion and rough surfaces increase the friction and
head loss.

#### Concrete Pipe

For longer lines, concrete pressure pipe may be more economical than
steel and is less subject to corrosion damage. Beveled pipe ends or
elbow specials are standard with the concrete pipe industry, so that
vertical or horizontal bends are readily laid. Thrust blocks to avoid
separation of the line should be provided at bend points where resultant
forces are significant. Joints should be of rubber‑gasket type to
withstand the internal pressure of the water and avoid leakage. The pipe
wall thickness and pipe strength must be sufficient to withstand
external pressures. Rubber‑gasket jointed pipe is also very suitable
where differential settlement of pump station and discharge line may be
anticipated.

#### Other Materials

Ductile iron pipe can be considered for use as discharge lines if
economically favorable. Outside of the station, options for conduit
material selection include concrete, corrugated metal, and plastic.

### Appurtenances

#### Couplings

The most common method of joining steel pipe is by forming or attaching
a flange to each end of the pipe, and then by bolting the flanges
together face‑to‑face, with a compressible gasket interposed between the
flanges to form a water‑tight joint.

For stormwater pump station construction, mild steel ring flanges of
moderate rating are satisfactory. These have flat faces. AWWA (American
Water Works Association) Standard C207‑55, Class D, is an applicable
specification, with such flanges being electrically‑welded to the
discharge piping. At least one pair of flanges is usually required in a
wet-pit station, such as when a check valve is included in the discharge
line. However, on occasions, flanges are not required.

Bolts and nuts (fasteners) required to make up flanges inside the pump
station may be specified as carbon steel, but the exposed threads should
be thoroughly cleaned and coated to prevent corrosion and remain
workable in the event dismantling is required. The added cost of
stainless steel fasteners is not usually warranted. Gasket material
should be specified as cloth-impregnated neoprene.

#### Flexible Couplings

To facilitate assembly of the steel piping system and to allow for
dimensional clearances and variations, it is necessary to include one or
more flexible couplings in each line. These couplings are frequently
known as Dresser couplings, relating to the name of the original
manufacturer of couplings of this type. A typical covering appears in
Figure 8‑1.

In general, the coupling consists of two flange rings spaced apart by a
sleeve and connected by a series of long parallel bolts around the
periphery. The sleeve fits loosely over the adjoining spigot ends of the
line pipe, and rubber ring gaskets are compressed between the flanges,
the sleeve and the line pipe. The gaskets form a water‑tight joint which
is tolerant of some clearance and misalignment of the spigot ends; hence
the description flexible. Just as the flexible coupling is essential for
making up the system, it permits ready disassembly of the system when
required. The flanges and sleeve should be epoxy coated (or galvanized).
To prevent corrosion, the bolts (or fasteners) are often of stainless
steel. The cost savings of mild steel or galvanized finish is a judgment
factor for the individual designer.

The flexible coupling is very limited in its resistance to longitudinal
forces or thrusts. It is often necessary to provide tie rods parallel to
it on each side. These are sometimes more‑or‑less integral with the
coupling and attached to the line pipe, but in a pump station it is
often convenient to provide the same effect by tie‑bolts between the
pump and the structural concrete, again embracing the coupling. The
sizing of the tie rods is determined by the cross‑sectional area of the
discharge line and the maximum discharge pressure of the pump. With
proper tie rods or other restraint from the pump station structure, the
flexible coupling will remain sealed and tight indefinitely while
subjected to shock, vibration, pulsation or other adjustments of the
discharge line.

![](media/image42.png){width="3.6368055555555556in"
height="2.8340277777777776in"}

43. []{#__RefHeading___Toc509049954 .anchor}Figure 8‑38. Typical
    flexible coupling

#### Steel-to-Concrete Adapter

A steel‑to‑concrete pipe adapter is required whenever such a change of
material is included in the design. The adapter is often conveniently
located in the concrete back wall of the pump station. This enables the
steel adapter to be adequately anchored in the thickness of the wall,
often with a circumferential ring or flange set on the center of the
wall to serve also as a water‑stop. Inside the station, the adapter may
have either a steel flange or a spigot‑end according to need. At some
point in its length, the steel pipe size of the adapter is enlarged and
at the downstream end a specially‑sized bell ring is welded on. The
sizing of the bell ring is performed by or for the concrete pipe
manufacturer so as to match the spigot end of his concrete pipe with
allowance for the necessary rubber gasket ring that ensures
water‑tightness under the discharge head. Internally, for a part of its
length, the adapter is cement mortar lined. The remainder is epoxy
coated.

The exterior of the adapter, which is inside the station, is also epoxy
coated, while the portion which is embedded in the wall or projecting
outside is coated with a cement mortar jacket.

### Preventing Reverse Flow

Some reverse flow may be unavoidable and could be sufficient to cause
reverse rotation of the pumps. The potential for this increases with
discharge line size. It is essential to check with the pump manufacturer
to determine if this is problematic and if so what mitigation measures
may be appropriate, such as:

-   a nonreverse ratchet fitted to the motor,

-   a time‑delay relay to prevent starting while the pump is running
    backwards, and

-   an automatic check valve.

If engine-driven pumps are used, a non‑reverse ratchet is required to
prevent engine backfire.

### Hydraulic Transients

A special problem may occur when a significant length of the discharge
line from a manifold has an elevation above the pump discharge elbow.
When pumps are shut down, the flow reversal toward the pumps could cause
dangerous water hammer surges if regular check valves are used. A pump
control valve is needed which opens and closes slowly and is controlled
so that the pump always stops and starts against a closed valve. Under
such a control system, the pump will operate at shutoff head for some
seconds on start‑up when water is in the line and the valve is opening.
The shutoff power must be considered when sizing the drivers for such an
installation. Pump curves usually show shut‑off power requirements.

If vertical pumps are used and the maximum static head exceeds about 10
m (33 ft) an air vacuum discharge valve will be needed if the intake is
not open to atmospheric pressure. In a stormwater pump, the intake is
usually open to the atmosphere, in which case a release valve is not
needed.

### Accessories

Other accessories which may be required in the discharge system are
air‑release and vacuum valves, flexible couplings and tie rods, flange
connections and fasteners, and steel‑to‑concrete pipe adapters.

### Valves 

A variety of valves are usually necessary and may include the following:

-   air and vacuum valves,

-   check valves, and

-   flap gates.

The designer should always consult with the pump manufacturer to
establish appropriate valve types and locations for the selected pumps.
The following provides a general discussion and some guidance.

#### Air and Vacuum Valves 

If a force main discharge line is used, or if high pressures in the
discharge line are anticipated, it is necessary to provide an air
release valve at the high point of a vertical pump discharge elbow. The
pump column at the high point of the elbow will contain air that needs
to be discharged to permit smooth starting of the pump and passage of a
full body of water through the check valve. This valve should be the
combination air and vacuum type, so that when the pump is shutdown, the
valve also permits entry of air to avoid the harmful formation of a
vacuum in the pump column. The sizing of these valves depends on the
pump capacity and the volume of air to be released. Figure 8‑2 provides
an illustration of a ball float air vent.

On short discharge lines, if a flap gate is used at the outlet
structure, a standard weight galvanized steel vent pipe installed
vertically on top of the end of the discharge pipe at the outlet
structure may be used in lieu of air‑vacuum valves. The pipe should be
capped on top to prevent entry of foreign objects, and should have holes
drilled as airports in the upper part of the pipe before galvanizing.

![](media/image43.png){width="3.0833333333333335in"
height="3.5118055555555556in"}

[]{#__RefHeading___Toc509049955 .anchor}Figure 8‑39. Ball float air
valve

#### Check Valves

Check valves are used to prevent backflow into the pumps and subsequent
recirculation. Any recirculation of flow can be harmful to the pump and
wasteful of energy. There are two types of location at which a check
valve is needed:

1.  In the discharge lines adjacent to the main pumps, such as where the
    system includes a manifold.

```{=html}
<!-- -->
```
18. In the discharge lines of sump pumps.

The check valves for the main pumps ensure that when any given pump is
not operating, the flow of water being delivered to the manifold by
other pumps cannot flow back through the non‑operating pump. The flow
velocity through the main check valves and consequently the head loss
that they add to the system should be minimized. Therefore, it is usual
to specify the main check valves to be the same size as the columns and
discharge elbows of the vertical pumps they protect. The slanting‑disc
type with an oil dashpot feature, to ensure slow closing (non‑slam)
action of the flapper, is the most preferred type of check valve as
shown in Figure 8‑3.

![](media/image44.png){width="4.904166666666667in"
height="3.4583333333333335in"}

44. []{#__RefHeading___Toc509049956 .anchor}Figure 8‑40. Rubber flapper
    swing check valve

The discharge lines of sump pumps are usually much smaller than the
discharge lines of the main pumps. For sump pumps, any regular non‑slam
check valves with cast‑iron body may be used, but the possibility of
clogging is a consideration. A ball‑type or rubber seated flapper‑type
check valve are preferred over the swing‑disc type because they are less
prone to jamming.

### Flap Gates and Flap Valves

Flap gates and flap valves are intended to close the end of a pipe
discharging into a receiving channel to prevent backwater from entering
the discharge line.

#### Flap Gates

Typically, a flap gate consists of a heavy metal casting, or lid,
circular in shape, hinged at the top from a body in such a manner as to
close the end of the discharge pipe by gravity. See Figure 8‑4. Water
being pumped through the discharge line will raise the flap sufficiently
to permit discharge. However, in so doing, there will be a head loss.
Manufacturer's data for head losses should be used for design.

Potential problems with flap gates include:

-   corrosion of the hinges resulting in poor operation,

-   corrosion of gate and frame resulting in poor sealing ability, and

-   debris can either prevent the gate from closing or prevent it from
    opening.

Where practicable, when using flap gates, the outlet should be above the
flood level of the outfall. If the outfall is tidal and the pump outlet
is lower than high tide elevation, conventional metal flap gates are not
preferred.

![](media/image45.png){width="5.611805555555556in"
height="2.707638888888889in"}

45. []{#__RefHeading___Toc509049957 .anchor}Figure 8‑41. Typical flap
    gate

#### Flap Valves

Flap valves serve the same function as flap gates. A typical flap valve
is shown in Figure 8‑5. Commercially available flap valves are usually
made out of neoprene. Generally, they require lower heads to operate
than metal flap gates. They are more suitable in a submerged, saltwater
environment than metal flap gates because of a lower propensity to
corrode. Additionally, they are less prone to fail due to clogging than
flap gates.

![](media/image46.png){width="1.8055555555555556in"
height="1.4166666666666667in"}

[]{#__RefHeading___Toc509049958 .anchor}Figure 8‑42. Rubber check valve

(Courtesy of Red Valve Company, Inc.)

### Outfall

The discharge line terminates at the outfall. For most highway
stormwater pump stations, the outfall should be one, or a combination of
the following:

-   open ditch or channel,

-   stream or river,

-   pond or lake,

-   gravity storm drain conduit, and

-   bay, estuary, or inlet.

Since design discharge line velocities will be high, about 3 m/s (10
fps), provision for permanent outlet protection should be considered.
Figure 8‑6 shows a typical outfall into an open channel. If the outfall
is a storm drain conduit, it is likely that only a junction box will be
necessary. Otherwise, the designer should refer to the FHWA publication
*Design of Rip Rap Revetment, HEC-11*^14^ for appropriate outfall
protection measures such as concrete or flexible liners.

![](media/image47.png){width="5.070833333333334in"
height="2.707638888888889in"}

[]{#__RefHeading___Toc509049959 .anchor}Figure 8‑43. Typical outlet
structure to channel

### Friction Loss Equations

There still are differences in the way in which friction losses through
pipes are calculated. These are:

-   Darcy-Weisbach

-   Hazen-Williams

-   Manning's Equation

The choice is up to the designer and the available manufacturer's data.
Generally, Hazen-Williams is used for the losses throughout the pump
station and Manning's is used for the storm drain conduit outside the
pump station.

#### Darcy-Weisbach

Probably the most accurate method is the Darcy-Weisbach method which
uses the following equation:

$h_{f} = \frac{\text{fLV}^{2}}{2\text{gD}}$ (8-2)

4.  

*h~f~* = friction head loss, m (ft)

*f* = friction factor

*L* = length of pipe, m (ft)

*V* = flow velocity, m/s (fps)

*g* = acceleration due to gravity, m/s^2^ (ft/s^2^)

The friction factor, f, is a function of Reynold's Number and flow type
(turbulent or laminar). The factor is selected using a Moody Chart. The
disadvantage of using this method is that the friction factor varies
with pipe size, type and velocity of flow. As a result, this method is
seldom used. However, if flow is in the turbulent range, friction
factors can be considered constant for a given pipe diameter.

#### Hazen-Williams

The Hazen-Williams equation for friction loss, the most widely used
equation, appears as follows:

$h_{f} = \frac{C_{u}V^{1\text{.}\text{85}}L}{C^{1\text{.}\text{85}}D^{1\text{.}\text{165}}}$
(8-3)

5.  

*h~f~* = friction loss, m (ft)

*L* = length of pipe, m (ft)

*C~u~* = unit conversion coefficient = 6.83 SI (3.022 English)

*V* = discharge velocity, m/s (cfs)

*C* = Friction factor

*D* = pipe diameter, m (ft)

The Hazen-Williams equation should only be used for turbulent flow and
is most applicable to water at a temperature of about 16 C (60 F). The
friction factor, C, for the Hazen-Williams varies with pipe material and
is typically in the range of 60 to 160. A design value of 100 is typical
for smooth steel pipe and smooth concrete pipe.

#### Manning's Equation

Manning's Equation can be used in the following form to compute friction
head loss:

$h_{f} = C\frac{V^{2}n^{2}}{R^{43}}L$ (8-4)

6.  

*h~f~* = friction loss, m (ft)

*C* = unit conversion factor, 1 SI (0.453 English)

*V* = flow velocity, m/s (fps)

*n* = Manning's roughness coefficient

*R* = hydraulic radius = area/wetted perimeter, m (ft)

*L* = length of conduit, m (ft)

For a circular conduit flowing full, the above simplifies to:

$h_{f} = 0\text{.}\text{75}C\frac{V^{2}n^{2}}{D^{43}}L$ (8-5)

7.  

D = pipe diameter, m (ft)

This method is considered less accurate than Darcy-Weisbach, but the
roughness coefficient does not vary with velocity, making it more
amenable. Typical design values of roughness (n) are 0.013 for concrete
and 0.011 for smooth steel. Generally, Manning's Equation is applied to
the storm drain conduit in the collection system and beyond the pump
station discharge line.

### Appurtenance Energy Losses

The most common approach to computing energy losses through
appurtenances such as valves and elbows is by use of a dimensionless
loss factor, K, applied to the velocity head as follows:

$h_{l} = K\frac{V^{2}}{2g}$ (8-6)

8.  

*h~l~* = friction loss through appurtenance, m (ft)

*K* = loss factor based on standard data or manufacturer's specified
data

*[V]{.smallcaps}* = velocity through appurtenance, m/s (fps)

*g* = acceleration due to gravity, m/s^2^ (ft/s^2^)

Where an appurtenance incurs a velocity change, such as a reducer or
expansion, the head loss calculation takes the following form:

$h_{l} = K\frac{\left( V_{2^{2}} - V_{1^{2}} \right)}{2g} = K\frac{\delta(V^{2})}{2g}$
(8-7)

9.  

*h~l~* = friction loss through appurtenance, m (ft)

*K* = loss factor based on standard data or manufacturer's specified
data

*V~1~* = entrance velocity to appurtenance, m/s (fps)

*V~2~* = exit velocity from appurtenance, m/s (fps)

*g* = acceleration due to gravity, m/s^2^ (ft/s^2^)

Table 8-2 presents a means of estimating loss coefficients for typical
appurtenances which may be used in the absence of manufacturer's
specified losses. Note that dual units are given. The coefficients are
based on a diameter given in millimeters for metric units and inches for
English units. The exponent, b, is dimensionless.

46. []{#__RefHeading___Toc509049857 .anchor}Table 8‑9. Loss coefficients
    for pipe appurtenances

```{=html}
<!-- -->
```
1.  Adapted from reference 17.

#### Example of Losses through Discharge Line

A discharge line consists of 20 m (65.6 ft) of 300 mm (12 in.) steel
pipe with two long radius flanged 90 degree elbows and a flanged swing
check valve. The pumping rate is 0.2 m^3^/s (7 cfs).

1.  The discharge velocity is:

$V = \frac{Q}{A} = \frac{0\text{.}2}{\frac{\pi}{4} \times 0\text{.}3^{2}} = 2\text{.}\text{83}$m/s
(9.3 fps)

1.  Using Equation 8-3, the friction loss through the pipe is:

$h_{f} = \frac{C_{u}V^{1\text{.}\text{85}}L}{C^{1\text{.}\text{85}}D^{1\text{.}\text{165}}}$$= \frac{6\text{.}\text{83} \times 2\text{.}\text{83}^{1\text{.}\text{85}} \times \text{20}}{\text{100}^{1\text{.}\text{85}} \times 0\text{.}3^{1\text{.}\text{165}}} = 0\text{.}\text{759}$m
(2.49 ft)

2.  Referring to Table 8-2, the loss expression for a long radius
    flanged 90 degree elbow is:

$h_{l} = \text{aD}^{- 0\text{.}\text{61}}\frac{V}{2g}^{2} = 3\text{.}\text{134} \times \text{300}^{- 0\text{.}\text{61}} \times \frac{2\text{.}\text{83}}{2 \times 9\text{.}\text{81}}^{2} = 0\text{.}\text{039}$m
(0.13 ft)

3.  The loss expression for a flanged swing check valve is:

$h_{l} = K\frac{V}{2g}^{2} = 2 \times \frac{2\text{.}\text{83}}{2 \times 9\text{.}\text{81}}^{2} = 0\text{.}\text{816}$m
(2.68 ft)

4.  The total losses through the discharge line are found by summating
    the individual losses:

Total loss =
$0\text{.}\text{759} + 2 \times 0\text{.}\text{039} + 0\text{.}\text{816} = 1\text{.}\text{653}$m
(5.42 ft)

## Total Dynamic Head and System Curve

### Total Dynamic Head

Total dynamic head, *TDH*, represents the total energy required to raise
the liquid from the intake to the discharge point. It comprises four
components:

-   static head,

-   friction head,

-   velocity head, and

-   pressure head.

Figure 8‑7 shows the components of total dynamic head and the following
equation presents the relationship:

$\text{TDH} = H_{s} + {\Sigma h}_{f} + h_{v} + {\delta H}_{p}$ (8-8)

10. 

*H~s~* = static head, m (ft)

*Σh~f~* = total head losses in pump and discharge line, m (ft)

*h~V~* = velocity head, m (ft)

*δH~p~* = pressure head change between outlet and intake, m (ft)

If the inflow and outflow are open to the atmosphere, the pressure head
change term, *δH~p~*, will be zero. This is usually the case for
stormwater pump stations.

![](media/image48.wmf){width="4.643055555555556in"
height="3.122916666666667in"}

47. []{#__RefHeading___Toc509049960 .anchor}Figure 8‑44. Components of
    total dynamic head

### System Head Curve

A system head curve represents the variation in total dynamic head with
respect to pumping rate. At zero flow, the total dynamic head is equal
to the total static head. As the pumping rate increases, the velocity
head, friction losses, and pump losses increase. Thus, the total dynamic
head increases with pumping rate as indicated in Figure 8‑8.

![](media/image49.wmf){width="5.240277777777778in"
height="2.198611111111111in"}

48. []{#__RefHeading___Toc509049961 .anchor}Figure 8‑45. Typical system
    head curve

For highway stormwater pump stations, the static head will vary between
the lowest elevation from which the stormwater is pumped and the maximum
storage elevation. There will be minimum and maximum system curves as
seen in Figure 8‑9.

![](media/image50.wmf){width="5.938194444444444in"
height="4.054166666666666in"}

49. []{#__RefHeading___Toc509049962 .anchor}Figure 8‑46. System curves
    for maximum and minimum static heads

### Procedure to Determine System Curves

When selecting specific manufacturer's pumps and piping:

-   the pump selection is dependent on the system head curve and power
    requirements,

-   the power requirements are dependent on the total dynamic head
    requirements,

-   the system head curve is dependent on total dynamic head,

-   the total dynamic head is dependent on the pump and pipe head
    losses, and

-   the head losses are dependent on the selected pumps and piping.

The designer must choose which way to proceed. The method presented here
begins by estimating the system curves before selecting manufacturer's
products. The assumptions are then checked for validity after selection.

1.  Determine the maximum static head, *H~s(max)~*. This is the
    difference in height between the outflow head level or discharge
    pipe elevation and the lowest pumping elevation (lowest pump stop
    elevation). Use the following table to determine the outflow head
    level.

  ----------------------- ----------------------- -----------------------
  If the centerline of    then set the outflow    Comment
  the discharge pipe is:  head level to:          

  lower than the          the estimated backwater Not preferable, but if
  estimated backwater     level from the          so, a flap gate will
  from the receiving      receiving water.        definitely be
  water (outfall),                                necessary.

  Lower than normal depth normal depth in the     As above.
  of flow in the outfall, outfall.                

  Higher than both normal centerline level of     This is the preferred
  depth of flow and       discharge pipe.         condition, where
  backwater in the                                practicable.
  outfall,                                        
  ----------------------- ----------------------- -----------------------

Example: A 2-pump system has a lowest pumping elevation of 20 m (65.6
ft), a maximum highwater in the pump station of 22 m (72.7 ft), a
centerline level of discharge pipe of 30 m (98.4 ft) and has a free
outfall. The sump is at atmospheric pressure. The maximum static head
is:

*H~s(max)~* = 30 -- 20 = 10 m (32.8 ft)

2.  Determine the minimum static head, *H~s(min)~*~.~ This is the
    difference in height between the outflow head level and the maximum
    highwater level in the wet well. The same conditions described in
    Step 1 apply to the outflow head level.

Example: The minimum static head is:

*H~s(min)~* = 30 -- 22 = 8 m (26.3 ft)

3.  Select a starting discharge, *Q*, that is greater than zero but
    lower than the target pump rate (*Q~p~*).

Example: Assuming previous values already computed, use a discharge,

*Q* = 0.2 m^3^/s (7 cfs).

4.  Compute the actual pipe velocity using the continuity equation as
    follows:

$V = \frac{Q}{A}$ (8-9)

11. 

*V* = pipe velocity, m/s (fps)

*Q* = discharge, m^3^/s (cfs)

*A* = pipe sectional area, m^2^ (ft^2^)

Example: Using a 300 mm pipe, the pipe velocity is:

*V* = 0.2 / (0.25 x π x 0.3^2^) = 2.83 m/s (9.3 fps)

5.  Compute the velocity head, *h~v~*, using the following equation:

$h_{V} = \frac{V^{2}}{2g}$ (8-10)

12. 

*h~V~* = velocity head, m (ft)

*g* = acceleration due to gravity, 9.81 m/s^2^ (32.2 ft/s^2^)

Example: The velocity head is:

*h~V~* = 2.83^2^ / (2 x 9.81) = 0.41 m (1.34 ft)

6.  Compute the head losses through pump discharge elements. Refer to
    Section 8.1.14.1- Example of Losses through Discharge Line.

Example: Referring to Section 8.1.14.1 - Example of Losses through
Discharge Line, the sum of pipe losses and appurtenance losses in the
discharge line at *Q* = 0.2 m^3^/s (7 cfs) is 1.65 m (5.4 ft).

7.  Compute *TDH~min~* and *TDH~max~* for the minimum and maximum static
    heads, *H~s(min)~* and *H~s(max)~*, respectively, using Equation
    8-8. Assuming the inlet and outlet are open to the atmosphere,
    *δH~p~* will be zero

Example: The maximum total dynamic head is:

$\text{TDH}_{(\text{max})} = H_{s(\text{max})} + {\Sigma h}_{f} + h_{v}$
= 10 + 1.65 + 0.41 = 12.06 m (39.6 ft)

The minimum total dynamic head is:

$\text{TDH}_{(\text{min})} = H_{s(\text{min})} + {\Sigma h}_{f} + h_{v}$
= 8 + 1.65 + 0.41 = 10.06 m (33.0 ft)

8.  Compute the arithmetic average (*TDH~ave~*) of the minimum and
    maximum total dynamic heads.

Example: The average total dynamic head is:

*TDH~(ave)~* = (10.06 + 12.06) / 2 = 11.06 m (36.3 ft)

9.  Using the full range of Q, repeat Step 4 to Step 8 until you have
    developed the *TDH* information for the full range of flows.

Example: Table 8‑3 shows the results of repeating the total dynamic head
computations for a range of discharges.

50. []{#__RefHeading___Toc509049858 .anchor}Table 8‑10. Example TDH
    calculations

![](media/image51.wmf){width="6.498611111111111in"
height="1.5888888888888888in"}

10. Plot the *TDH~max~*, *TDH~min~*, and *TDH~ave~*, versus discharge.
    This is the system curve plot.

Example: Figure 8‑10 shows the system curve plot for the values in Table
8‑3.

![](media/image52.wmf){width="5.710416666666666in"
height="3.8979166666666667in"}

51. []{#__RefHeading___Toc509049963 .anchor}Figure 8‑47. Example system
    curve

```{=html}
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```
11. Establish the target design variables *TDH~ave~*, the average of
    *TDH~max~* and *TDH~min~*, for the target pump capacity, *Q~p~*.
    (That is, the capacity of one pump, not total pumping rate).

Example: Referring to Table 8‑3, at a design pump rate of 0.2 m^3^/s
(7cfs):

TDH~(max)~ = 12.06 m ( 39.6 ft)

TDH~(min)~ = 10.06 m ( 33.0 ft)

TDH~(ave)~ = 11.06 m (36.3 ft)

## Pump Characteristics

### Cavitation

Cavitation is a hydraulic phenomenon in which vapor bubbles form and
suddenly collapse (implode) as they move through a pump impeller.
Implosions occur on each of the vanes of the impeller causing excessive
noise. The hydraulic effect on the pump is a significant reduction in
performance. The mechanical effects can include shock waves and
vibration which may result in damage to the impeller vanes, bearings,
and seals.

Cavitation occurs when the pressure in the liquid is reduced to the
liquid's vapor pressure such that boiling begins to occur, even though
the liquid's temperature may not have changed. Therefore, to prevent
cavitation, it is necessary to ensure that the pressure does not drop to
the liquid's vapor pressure.

The primary causes of cavitation in highway stormwater pump stations
include the following:

-   the impeller vane travels faster than the liquid,

-   suction is restricted,

-   the required NPSH is either equal to or greater than the available
    NPSH, and

-   the specific speed is too high for optimum design parameters.

### Vortexing

A vortex can occur at the impeller and may extend to the surface of the
liquid. If this occurs, air will be sucked into the pump. The effects
can be similar to cavitation: reduced hydraulic efficiency and increased
wear on the pump. Dicmas identifies three stages of vortexing^3^:

-   Type I -- first inception of vortexing in which bubbles of air are
    drawn towards the pump

-   Type II -- vortexes form for a period of less than 30 seconds,
    pulling in air and possibly debris, and

-   Type III -- continuous vortexing draws in large volumes of air and
    possibly debris.

Figure 8‑11 shows Type I and:Type III vortexing. Type II is a
combination of Type I and Type III.

![](media/image53.png){width="6.029861111111111in" height="2.56875in"}

52. []{#__RefHeading___Toc509049964 .anchor}Figure 8‑48. Types of vortex

It is preferable to avoid vortexing. However, Type I vortexing will
generally not harm the pump and no significant reduction in performance
is expected and thus can be deemed acceptable. Type II vortexing can
reduce pump performance intermittently and Type III vortexing can cause
serious reductions in pump performance along with cavitation, noise and
vibration. The potential for vortexing is limited by providing adequate
submergence (See 8.3.6 - Submergence).

### Net Positive Suction Head Required

Net positive suction head required (NPSHR) is the head above vapor
pressure head required to ensure that cavitation does not occur at the
impeller. The value is specific to each pump inlet design. It is
independent of the suction piping system. The NPSHR is determined by
bench scale tests of geometrically similar pumps operating at a constant
speed and discharge with varying suction heads. The development of
cavitation is usually indicated by approximately a 3% drop in the head
developed at the suction inlet valve. The NPSHR is specified by the
manufacturer.

### Net Positive Suction Head Available

Net positive suction head available (NPSHA) is the head available above
vapor pressure head to move a liquid into the impeller unit of the pump.
It is necessary to ensure that the NPSHA exceeds the NPSHR to prevent
cavitation. The following equation is used to compute NPHSA:

$\text{NPSHA} = H_{\text{pa}} + H_{s} - h_{f} - H_{\text{vp}}$ (8-11)

13. 

*H~pa~* = the atmospheric pressure head on the surface of the liquid in
the sump -- m (ft).

*H~s~* = static suction head of liquid. This is height of the surface of
the liquid above the centerline of the pump impeller -- m (ft)

*h~f~* = total friction losses in the suction line -- m (ft)

*H~vp~* = the vapor pressure head of the liquid at the operating
temperature -- m (ft)

Figure 8‑12 shows the relationship between the variables described in
Equation 8-12. If the liquid level is below the centerline of the
impeller, the static head is negative and is termed static suction lift.
Table 8‑4 provides vapor pressure heads for water at atmospheric
pressure. In reality, the vapor pressure changes with air pressure,
however, these values are reasonable for use with typical stormwater
pump stations.

![](media/image54.wmf){width="3.98125in" height="2.8291666666666666in"}

53. []{#__RefHeading___Toc509049965 .anchor}Figure 8‑49. Net positive
    suction head available

Example: the lowest pumping level is 2.4 m (8 ft) above the proposed
pump impeller, there is no suction line and bell losses are assumed to
be negligible, atmospheric pressure is 10.3 m (33.9 ft) of water, and
the vapor pressure head of water is 0.236 m (0.84 ft), the *NPSHA* is:

$\text{NPSHA} = H_{\text{pa}} + H_{s} - h_{f} - H_{\text{vp}}$ = 10.3 +
2.4 -- 0 -- 0.236 = 12.46 m (40.9 ft)

54. []{#__RefHeading___Toc509049859 .anchor}Table 8‑11. Vapor pressure
    heads for water

  ----------------- ----------------- ----------------- -----------------
  **Temperature**                     **Vapor Pressure  
                                      Head**            

  **Celsius**       **Fahrenheit**    **m**             **ft**

  0                 32                0.062             0.204

  15                59                0.712             0.565

  20                68                0.236             0.774

  23.9              75                0.305             1.00

  37.8              100               0.661             2.17
  ----------------- ----------------- ----------------- -----------------

### Net Positive Suction Head Margin

Net positive suction head margin is the amount by which the NPSHA
exceeds the NPSHR. A positive margin is necessary; however, it is not
practicable to define a recommended magnitude of the margin because of
the many variables that affect the potential for vortexing and
cavitation. The designer should check with the manufacturer of the
selected pumps for recommendations of an appropriate margin based on the
pumps and the conditions under which they will operate.

### Submergence

Submergence is the static head of water required above the intake bowl
or volute of the pump to prevent cavitation and vortexing. The designer
must ensure that the minimum static head provides a NPSHA (see Section
8.3.4 - Net Positive Suction Head Available) that is an established
margin (see Section 8.3.5 Net Positive Suction Margin) greater than the
manufacturer's specified NPSHR (see Section 8.3.3 - Net Positive Suction
Head Required). Also, refer to Section 9.1.2 - Sump Width for
determination of required minimum submergence using Hydraulic Institute
standards. The designer should use the criterion that creates the higher
submergence.

### Specific Speed

Specific speed, *N~s~*, is often quoted as a dimensionless design index
for pump impellers. However, strictly speaking, it has dimensions that
are in terms of:

\[L^0.75^T^-0.5^\] x revolutions per minute

where L represents units of length, and T represents units of time.

Specific speed is used to identify an upper limit on the shaft speed for
any particular combination of total head, flow, and suction conditions.
The specific speed is determined using the following equation:

$N_{s} = C\frac{\text{NQ}^{0\text{.}5}}{H^{0\text{.}\text{75}}}$ (8-12)

14. 

*N* = pump speed, rpm

*Q* = pump capacity at Best Efficiency Point (BEP), m^3^/hr (gpm)

*H* = pump head at BEP, m (ft)

*C* = unit factor = 0.861 \* (1)

\* For consistency with US manufacturers' pump data, a unit factor for
metric units is given to result in a consistent value that is really in
English units. The designer should verify the derivation and
manufacturer's use of specific speed.

By applying pump affinity laws, a pump designer can predict the change
in performance of a pump in response to changing speed. Discussion of
affinity laws is beyond the scope of this manual. For a discussion,
refer to a text such as *Pump Performance Characteristics and
Applications*.^4^

### Suction Specific Speed

Suction Specific Speed, *N~ss~*, is a dimensionless index that is both
representative of the geometry of the suction side of the impeller, and
is used to determine the form and proportions of the impeller. The index
can be used to select a pump maximum speed that will likely yield the
smallest size of pump for the design conditions. It is determined using
the following equation:

$N_{\text{ss}} = C\frac{\text{NQ}^{0\text{.}5}}{\text{NPSHR}^{0\text{.}\text{75}}}$
(8-13)

15. 

*NPSHR* = net positive suction head required, m (ft)

*N~ss~* = suction specific speed, rpm

*N* = pump speed, rpm

*Q* = pump capacity at Best Efficiency Point (BEP), m^3^/hr (gpm)

*C* = unit factor = 0.861 \* (1)

### Selection of Impeller Type

Table 8‑5 indicates the ranges of specific speed over various impellers
that are recommended for use.

55. []{#__RefHeading___Toc509049860 .anchor}Table 8‑12. Specific speed
    range for impellers

  ----------------------- ----------------------- -----------------------
  Impeller Type           Specific Speed          

                          Upper                   Lower

  Axial Flow              20,000                  8,500

  Mixed Flow (open)       10,000                  5,000

  Mixed Flow (closed)     6,200                   4,000

  Centrifugal             4,100                   2,500
  ----------------------- ----------------------- -----------------------

### Pump Performance

Pump performance is measured as the variation in pumping capacity with
respect to total dynamic head. Pump performance is a function of the
following pump characteristics:

-   pump type,

-   pump size,

-   impeller size, and

-   speed.

Pump performance can be shown either as a single line curve for one
impeller diameter or as multiple curves for the performance of several
impeller diameters in one casing. Figure 8‑13 shows a typical single
pump performance curve.

Pump performance is measured and specified by the pump manufacturer.
Most manufacturers' performance curves depict the total head developed
by the pump, the brake power required to drive it, the derived
efficiency and the net positive suction head required to drive it over a
range of flows at constant impeller speed. Figure 8‑14 shows a
simplified version of a typical manufacturer's performance
characteristics plot which presents performance curves for varying
impeller size. Pump efficiency is also shown. The point at which maximum
efficiency is achieved is represented by the best efficiency point, BEP,
as shown in Figure 8‑14.

![](media/image55.wmf){width="5.002777777777778in"
height="2.282638888888889in"}

56. []{#__RefHeading___Toc509049966 .anchor}Figure 8‑50. Typical pump
    performance curve

![](media/image56.wmf){width="6.241666666666666in"
height="4.274305555555555in"}

57. []{#__RefHeading___Toc509049967 .anchor}Figure 8‑51. Simplified
    manufacturer's pump performance curves

### Design Point and Operation Range

The design point is the target total dynamic head and discharge
superimposed on the performance curve plot. The performance curve that
is closest to the design point would be the characteristic curve for the
desired pump. Alternatively, the manufacturer can usually trim the
impeller to best meet the design point. If the efficiency at which the
design point occurs is low, then the design should identify a different
pump speed or pump type.

If a single pump were to operate with constant static head, the design
point would be determined as the point of intersection of the system
curve and selected performance curve, as shown in Figure 8‑15. This
situation is not applicable to highway stormwater pumps because the
static head in a stormwater pump station varies during the operation of
the pump station. The following two approaches are applicable to highway
stormwater pumps depending on the configuration of the discharge piping.

![](media/image57.wmf){width="5.1506944444444445in"
height="3.522222222222222in"}

58. []{#__RefHeading___Toc509049968 .anchor}Figure 8‑52. Design point

When two or more pumps connected to a common discharge line are
operating and the static head changes over a limited range, the design
point will move from A, for the first pump operating alone, to B, with
both pumps operating at the minimum static head, as indicated in Figure
8‑16. This represents an operating range. This case is typical for a
stormwater pump station in which all pumps are connected to a common
discharge line using a manifold.

![](media/image58.wmf){width="5.170138888888889in"
height="3.5416666666666665in"}

59. []{#__RefHeading___Toc509049969 .anchor}Figure 8‑53. Operating range
    for two pumps and common discharge line

When two or more pumps with separate discharge lines are operating and
the static head changes over a limited range, the range over which the
pumps must operate is from A to B as shown in Figure 8‑17. This case is
typical for a stormwater pump station in which each pump discharges to
the outfall via separate discharge lines.

![](media/image59.wmf){width="5.05625in" height="3.463888888888889in"}

60. []{#__RefHeading___Toc509049970 .anchor}Figure 8‑54. Operating range
    for pumps with separate discharge lines

### Example of Pump Selection

An example is shown in Figure 8‑18. The design pump rate is 800 m^3^/hr
(7.9 cfs) at an average total dynamic head of 16 m (52.5 ft). The
minimum, average and maximum total dynamic head curves (system curves)
are superimposed on a simplified pump performance chart. The pump curve
for a 425 mm (16.7 in.) impeller provides the design point (Point A).
When the system operates at maximum total dynamic head, the actual
pumping rate will be less at about 750 m^3^/hr (7.36 cfs) - Point B.
When the system operates at minimum total dynamic head, the actual
pumping rate will be greater at about 840 m^3^/hr (8.25 cfs) - Point C.
Points A and B lie under the 40 kW (54 hp) power curve, but Point C lies
between the 40 kW (54 hp) and 50 kW (67 hp) power curves. Thus, in order
to ensure adequate power for the range of operations, a motor rated for
50 kW (67 hp) will be necessary.

![](media/image60.wmf){width="5.852777777777778in"
height="4.002083333333333in"}

61. []{#__RefHeading___Toc509049971 .anchor}Figure 8‑55. Manufacturer's
    performance curves

### Procedure to Select Manufacturer's Pumps and Discharge Piping

You will need the following information to select a pump:

-   desired pump type,

-   manufacturer's catalogues of performance curves,

-   design *TDH~ave~*, *TDH~max~*, and *TDH~min~*~,~ and

-   design pump capacity.

1.  Compute the Net Positive Suction Head Available using Equation 8-11.

Refer to the example in 8.3.4 Net Positive Suction Head Available.

2.  Tabulate the following data:

-   Approximate system head curve (Example: the *TDH~max~*, *TDH~ave~*,
    and *TDH~min~* are 18.5 m (60.7 ft), 17.5 m (57.4 ft), and 16.5 m
    (54.1 ft), respectively.

-   Design Capacity (Example: Individual pump capacity = 0.8 m^3^/s
    (28.3cfs))

-   Desired pump type (Example: try a submersible pump)

3.  Browse manufacturer's catalogues for the family of pump performance
    curves that cover the desired pump capacity and operating range
    (*TDH~max~ to TDH~min~*).

4.  Select a performance curve that crosses through or near the design
    pump capacity at the design *TDH~ave~*. This is the design point. If
    the manufacturer can trim the impellers to meet your exact design
    point, you can establish an intermediate performance curve by
    interpolation. If the design point falls on the performance curve at
    a low efficiency, you should preferably look for other pumps. The
    selection at this point is tentative.

Example: Figure 8‑19 is a manufacturer's performance curve for a 715 rpm
submersible pump. Assuming the manufacturer will trim the impeller, the
design point is at a head of 17.50 m (57.4 ft) and discharge of 0.800
m^3^/s (28.3 cfs). The required impeller size would be about 610 mm
(24.0 in.) and the rated efficiency is about 85.7 %. Note that the motor
power required would be 186 kW (250 hp).

5.  For the selected pump curve, determine the operating discharges at
    *TDH~max~* and *TDH~min~*.

Example: Using Figure 8‑19, at *TDH~max~ =* 18.5 m (60.7 ft), *Q~max~*
\~0.75 m^3^/s (26.5 cfs) and at *TDH ~min~* = 16.5 m (54.1 ft), *Q~min~*
\~ 0.84 m^3^/s (29.7 cfs). This represents the operating range for the
selected pump.

![](media/image61.png){width="5.665277777777778in" height="8.3in"}

62. []{#__RefHeading___Toc509049972 .anchor}Figure 8‑56. Pump
    manufacturer's curve

    (Courtesy of Flygt Corporation)

### Pump Bell/Intake Diameter

For design of highway stormwater pump stations, the recommended approach
is to select the pump from manufacturer's curves as discussed in Section
8.3.13 - Procedure to Select Manufacturer's Pumps and Discharge Piping.
Once the pump is selected, the bell or volute size can be identified
from the manufacturer's specifications. The bell or intake volute
diameter should then be checked to determine if the intake velocity
falls within the recommended range indicated in Table 8‑6.

63. []{#__RefHeading___Toc509049861 .anchor}Table 8‑13. Recommended pump
    intake velocities

Adapted from reference 15

+-----------------------------------+----------------------------------+
| If the pump flow is:              | The intake velocity can be:      |
+-----------------------------------+----------------------------------+
| \< 0.315 m^3^/s (5000 gpm)        | 0.6 -- 2.7 m/s (2.0 -- 9.0 fps)  |
+-----------------------------------+----------------------------------+
| 0.315 -- 1.26 m^3^/s              | 0.9 -- 2.4 m/s                   |
|                                   |                                  |
| (5000 -- 20,000 gpm)              | (3.0 -- 8.0 fps)                 |
+-----------------------------------+----------------------------------+
| \> 1.26 m^3^/s (20,000 gpm)       | 1.2 -- 2.1 m/s (4.0 -- 7.0 fps)  |
+-----------------------------------+----------------------------------+

If the intake velocity at the bell is higher than the higher limit
established above, it will be necessary either to select a different
pump, or add an umbrella to the pump. If the velocity is lower than the
lower limit established above, the pump size may be excessive and the
designer should consider selecting a pump with a small bell diameter,
which, in turn, will reduce the required sump dimensions.

### Power and Efficiency

Three terms are often used when referring to power for pumps:

-   Water power

-   Brake power

-   Wire-to-water power

#### Water Power

Water Power WP (water horsepower WHP in English units) is the output
power of a pump handling a given liquid at a given total dynamic head
and discharge. It is determined using the following equation:

$\text{WP} = \frac{1}{C_{u}}\gamma Q\left( \text{TDH} \right)$ (8-14)

16. 

*WP* = water power, kW (hp)

*C~u~* = unit conversion factor, 1000 (550)

*γ* = specific weight of liquid, N/m^3^ (lbf/ft^3^)

*Q* = discharge, m^3^/s (cfs)

*TDH* = total dynamic head, m (ft)

Refer to Table 8‑7 for values of specific weight.

64. []{#__RefHeading___Toc509049862 .anchor}Table 8‑14. Specific weight
    of water

![](media/image62.wmf){width="3.3201388888888888in"
height="2.6569444444444446in"}

Example: The design pump rate is 0.2 m^3^/s, the design *TDH~ave~* is
11.06 m (36.3 ft), and the specific weight of water is 9798 N/m^3^, the
water power is:

*WP~ave~* = 9798 x 0.2 x 11.06 / 1000 = 21.7 kW (29.1 hp)

Similarly at *TDH~max~ =*12.06 m (39.6 ft)*, WP~max~ =* 23.7 kW (31.8
hp), and at *TDH~min~ =*10.06 m (33.0 ft)*, WP~max~ =* 19.7 kW (26.4 hp)

#### Brake Power

Brake power, BP (brake horsepower, BHP, in English units) is the actual
amount of power required to be supplied to the pump to maintain the
water power. Brake power is the sum of the water power and power
required to overcome losses incurred by the pump. Pump losses include:

-   hydraulic losses,

-   volumetric losses,

-   mechanical losses, and

-   disk friction.

Hydraulic losses incurred by the impeller and volute or diffuser are due
to friction and momentum changes. Volumetric losses for centrifugal
pumps are associated with leakage from the discharge side to suction
side of the impeller. Mechanical losses result from friction between the
moving parts of pumps such as between bearings, packing, and seals. Disk
friction is the resistance between the impeller and casing.

The net effect of the above losses is described by efficiency that
varies with pump type, *TDH* and flow rate. The efficiency is described
as the ratio of pump power output to pump power input:

$\eta = \frac{\text{WP}}{\text{BP}}$ (8-15)

17. 

*η* = pump efficiency

*WP* = water power, kW (hp)

*BP* = brake power, kW (hp)

The pump efficiency, *η*, is established by the manufacturer and is
usually provided in the form of iso-efficiency lines on the pump
performance curves such as the set shown in Figure 8‑19.

Example: For the manufacturer's pump selected in Section 8.3.13 -
Procedure to Select Manufacturer's Pumps and Discharge Piping, the rated
efficiency,* η*, is 75%, and using the water power computed in Section
8.3.15.1 - Water Power, the design brake power is:

*BP~ave~ =* 21.7/0.75 = 28.9 kW (38.6 hp)

Similarly,

*BP~max~* = 31.6 kW (42.1 hp), and

*BP~min~* = 26.3 kW (35.2 hp)

Thus, the selected pump requires a motor power of at least 31.6 kW (42.1
hp) to ensure enough power to handle the operating range. For this pump
(Figure 8‑19), the minimum motor power available is 67 kW (90 hp), which
will suffice.

#### Wire-to-Water Power

In addition to the inefficiency of the pump, there is a loss of power
associated with the motor. These losses are described by the motor
efficiency, η~e~, as the ratio of output power to the motor and input
power to the motor. The wire-to-water power, then, is the total
electrical power required to maintain the discharge and total dynamic
head:

$\text{WWP} = \frac{\text{WP}}{\text{ηη}_{e}}$ (8-16)

18. 

*WWP* = wire-to-water power, kW (hp)

*WP* = water power, kW (hp)

*η* = pump efficiency

*η~e~* = motor efficiency

Example: The maximum water power required is 23.7 kW (31.6 hp), the
rated hydraulic efficiency is 75 % and the motor efficiency is 80%. The
wire-to-water power is:

WWP = 23.7/(0.75 x 0.8) = 39.5 kW (52.7 hp)

Some manufacturers may provide TDH, BP, and efficiency curves on a
single plot for a single specific pump, impeller size, and speed.
However, a majority of manufacturers present multiple performance
curves, power curves and efficiency curves on a single plot, such as is
shown in Figure 8‑14. Generally, the iso-power lines represent only
commercially available electric motor sizes. Also, the designer must
note that the power curves relate to water at a specific gravity of 1.
If the specific gravity of the liquid to be pumped is different, the
power must be adjusted accordingly. Once a pump size is selected, it is
usual to select a motor size based on the highest power curve within
which the full performance curve of the selected pump size will operate.
For electric motors, the designer may estimate the wire-to-water power
by dividing the brake power by an assumed electrical efficiency of 0.8.

This page intentionally left blank.

# SUMP DIMENSIONS AND SYSTEM CHECKS

## Sump Size and Clearance Criteria

The premise for the criteria is the pump bell diameter, D (Section
8.3.14 - Pump Bell/Intake Diameter). Generally, the most conservative of
the manufacturer's specification for a specific pump and the Hydraulic
Institute standards should be followed. The sump dimensions and
clearances currently recommended by the Hydraulic Institute appear in
Pump Intake Design^15^. The designer should refer to this document for
detailed design. However, the appropriate criteria for basic stormwater
pump station sumps appear here. The Hydraulic Institute recommends model
testing for sump and pump configurations and conditions that deviate
from their recommended criteria.

### Sump Depth

The depth of the sump system is controlled by one or more of the
following:

-   invert elevation of the inlet

-   typical wet well detail used by highway agency (location of trash
    racks etc.),

-   volume required for cycling where no other significant storage is
    provided (See, Usable Storage),

-   submergence requirements of the pumps used, and

-   clearance required for the pump intake bell.

Hydraulic Institute recommendations^15^ indicate that the invert
elevation of the intake line (from the collection system or storage
unit) should be no lower than the lowest pumping level. Since it is also
desirable to maximize the storage within the storage system, the
preference is to set the lowest pumping level at or slightly above the
invert of the intake. The sump system floor should be set no lower than
needed to accommodate the above conditions unless foundation
requirements indicate otherwise.

### Sump Width

The minimum total sump width is the sum of required pump bay widths and
divider wall thickness for a rectangular wet well. Refer to Section
9.1.4 - Rectangular Sumps for required pump bay width. For a circular
sump, the width is the diameter of the sump, which can be established by
referring to Section 9.1.5 - Circular Sumps.

#### Sump Velocity

Water velocity in the sump should be low, preferably about 0.3 m/s (1.0
ft/s). The Hydraulic Institute^15^ recommends a maximum velocity of 0.5
m/s (1.5 ft/s) for clear water. Several ways to reduce velocities
include:

-   increasing the inflow conduit size,

-   using baffles,

-   providing transition from inflow conduit to the wet well, and

-   extending the length of the wet well.

The Hydraulic Institute^15^ suggests attaining approach velocities of
1.0 m/s (3 ft/s) or more in the storage unit and pump bays of
rectangular sumps containing sediment-laden water unless other measures
are taken.

### Submergence Depth

The minimum height of water above the pump intake bowl or volute, S,
should be the higher of that required by the manufacturer for net
positive suction head (See 8.3.6 Submergence) and the height determined
using Equation 9-1, which is based on Hydraulic Institute standards^15^
for pump bell velocities falling in the range shown in Table 8‑6.

$S = D + \frac{C_{u}Q_{p}}{D^{1\text{.}5}}$ (9-1)

19. 

*S* = height from lowest pumping level to pump bell/volute, m (ft)

*D* = outside diameter of pump bell/volute, m (ft)

*C~u~* = unit conversion coefficient = 0.935 (0.516)

*Q~p~* = individual pump capacity, m^3^/s (cfs)

### Rectangular Sumps

#### Limitations of Rectangular Sump Criteria

The Hydraulic Institute recommends use of the rectangular sump dimension
criteria below the following pumping limits:

Total pumping capacity per wet well of 6.3 m^3^/s (223 cfs)

Individual pump capacity of 2.5 m^3^/s (89 cfs)

The Hydraulic Institute recommends that model tests be performed for
stations that exceed the above limits. If the design exceeds these
limits, then the designer should check to see if the pump manufacturer
has performed tests to establish sump criteria. If not, the designer
should do one of the following:

select another manufacturer's pumps with appropriate sump criteria,

use a larger number of smaller capacity pumps,

increase the storage unit size to reduce total pumping requirements, or

use multiple and separate wet wells.

#### Dimensions for Rectangular Sumps

65. 

Figure 9‑1 identifies the recommended sump dimensions for a typical
newly-designed rectangular sump. The dimensions apply to sumps used for
wet-stations. Table 9-1 presents the Hydraulic Institute criteria for
the sump dimensions. The dimensions apply to sumps used for wet-pit
stations and to dry-pit stations with less than five diameters of
suction piping. If fixture details, structure details or some other need
results in a wider bay entrance, the width of the bay at the pump
bell/volute, w, should be reduced to twice the bell/volute diameter as
shown in Figure 9‑2.

66. []{#__RefHeading___Toc509049863 .anchor}Table 9‑15. Rectangular sump
    dimensions

```{=html}
<!-- -->
```
2.  Adapted from reference 15

  ----------- ------------------------------------------ ------------------
  Dimension   Description                                Recommended Value

  A           Distance from centerline of pump inlet     5D
              bell/volute to sump entrance               

  a           Length of constricted bay section at pump  2.5D

  B           Clearance from back wall to centerline of  0.75D
              pump inlet bell/volute                     

  C           Clearance between pump inlet bell and sump 0.3D - 0.5D
              floor                                      

  D           Outside diameter of pump inlet bell/volute See 8.3.14 Pump
                                                         Bell/Intake
                                                         Diameter

  H~min~      Minimum water depth in sump                S + C

  h           Minimum height of constricted bay section  Greater of H or
                                                         2.5D

  S           Minimum pump inlet bell submergence        See Equation 9-1

  W           Pump inlet bay width                       ≥ 2D

  w           Minimum width of constricted bay section   2D

  X           Pump inlet bay length                      ≥ 5D

  Y           Distance from centerline of pump inlet     ≥ 4D
              bell/volute to screen                      

  Z~1~        Distance from centerline of pump inlet     ≥ 5D
              bell/volute to diverging walls             

  Z~2~        Distance from centerline of pump inlet     ≥ 5D
              bell/volute to sloping floor               

  α           Angle of floor slope                       0 -- 10 degrees

  β           Angle of wall convergence                  0 -- 10 degrees

  φ           Angle of convergence from constricted area 10 degrees max.
              to pump bay walls                          
  ----------- ------------------------------------------ ------------------

![](media/image63.png){width="5.00625in" height="5.00625in"}

67. []{#_Ref452692259 .anchor}

68. Figure 9‑57. Recommended rectangular sump

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3.  Adapted from reference 15

![](media/image64.png){width="5.00625in" height="5.00625in"}

69. []{#__RefHeading___Toc509049974 .anchor}Figure 9‑58. Filler walls
    for pump bay

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4.  Adapted from reference 15

#### Contracting versus Expanding Sump Entrances

Figure 9-1 presents a contracting entrance in which an angle, *β*, is
applied to converging walls. This would be appropriate when the inflow
conduit is wider than the width of the sump.

When the inflow conduit is narrower than the sump width, the flow must
expand when entering the sump. A transition with diverging walls of at
least 10 degrees is recommended. Baffles may be used to help reduce
velocities and distribute the flow.

#### Pump Bay Velocity

The velocity in the pump bay should be 0.5 m/s (1.5 fps) or less. The
inflow velocity to a pump bay is determined using the following
equation:

$V_{s} = \frac{Q_{p}}{\text{WH}_{\text{min}}}$ (9-2)

20. 

*V~s~* = average velocity in pump bay, m/s (fps)

*Q~p~* = individual pump capacity, m^3^/s (cfs)

*W* = pump bay width, m (ft)

*H~min~* = depth from the lowest pumping level to the sump floor, m (ft)

#### Example of Rectangular Sump Dimensions

It is necessary to establish sump dimensions and clearance values for a
rectangular wet well in which will be placed two 0.2 m^3^/s (7 cfs)
pumps with bell diameters of 600 mm (2 ft) each. The lowest pump stop
elevation (minimum water level in the sump) is 16.750 m (54.95 ft). The
pumps will be separated by a divider wall, the spacing of which is to be
established. No screen is used inside the wet well. The inflow line is a
1.2 m diameter pipe with a clear and straight length of 160 m. The
invert elevation of the inflow line at the sump is 16.75 m (54.95 ft).

The total pumping capacity is 2 x 0.2 = 0.4 m^3^/s (14 cfs)

The velocity at the bell face is:

$V = \frac{Q}{A}$ = 0.2/(π x 0.6^2^ / 4) = 0.71 m/s (2.3 fps)

Referring to Table 8‑6, the flow is less than 0.315 m^3^/s and the
velocity is between 0.6 and 2.7 m/s. Also, the individual pumping rate
is less than 2.5 m^3^/s (89 cfs) and the total pumping rate is less than
6.3 m^3^/s (223 cfs). Thus the Hydraulic Institute recommended sump
dimensions apply.

Using Equation 9-1, the required minimum submergence is:

$S = D + \frac{C_{u}Q_{p}}{D^{1\text{.}5}}$ = 0.6 + 0.935 x 0.2 /
0.6^1.5^ = 1.0 m (3.3 ft)

The remaining appropriate variables appear in Table 9‑2 based on the
criteria in Table 9-1.

70. []{#__RefHeading___Toc509049864 .anchor}Table 9‑16. Sample
    rectangular sump calculations

  ----------- ------------------------------------------ ------------------
  Dimension   Calculation                                Magnitude, m (ft)

  A           5 x 0.6                                    3 (9.8)

  B           0.75 x 0.6                                 0.45 (1.5)

  C           0.3 x 0.6                                  0.18 (0.6)

  H~min~      1.0 + 0.18                                 1.18 (3.9)

  W           2 x 0.6                                    1.2 (3.9)

  X           5 x 0.6                                    3 (9.8)

  Z~1~, Z~2~  5 x 0.6                                    3 (9.8)
  ----------- ------------------------------------------ ------------------

Assuming a divider wall thickness of 150 mm (6 in.), the internal sump
width, W~s~, would need to be:

W~s~ = 2 x 1.2 + 0.15 = 2.55 m (8.4 ft)

The preliminary elevation of the sump floor is set a height H~min~ below
the lowest pumping elevation:

Sump floor elevation = 16.75 - 1.18 = 15.57 m (51.08 ft)

Note: it will be necessary to check the net positive suction head
available (NPSHA) with the net positive suction head required (NPSHR).
Referring to Figure 8‑19, for a design discharge of 0.2 m^3^/s (7 cfs)
which is 200 liters/s (3193 gpm), the NPSHR is about 3 m (9.8 ft). This
is lower than the NPSHA of 12.46 m (40.9 ft) calculated in Step 1 of
Section 8.3.13 Procedure to Select Manufacturer's Pumps and Discharge
Piping. Thus the proposed sump floor elevation of 15.57 m (51.08 ft) is
satisfactory.

The height difference between the sump floor and inflow line is 1.18 m
(3.9 ft). Using a floor slope of 10 degrees:

Required vertical transition length = 1.18 / tan (10) = 6.69 m (22 ft)

The centerline of the inflow line is to enter the sump at mid-width to
ensure even flow distribution. If the inflow conduit is wider than the
sump width, a horizontal transition is needed to contract the flow from
the inflow line to the sump. Using a suggested horizontal transition
(expansion) of 10 degrees:

Horizontal transition length = (2.55 -- 1.2) / 2 / tan (10) = 3.83 m
(12.56 ft)

Figure 9‑3 shows the resulting sump dimensions.

![](media/image65.wmf)

71. []{#__RefHeading___Toc509049975 .anchor}Figure 9‑59. Dimensions for
    sump example (NTS)

#### Accommodation of Solids-bearing Water in Rectangular Wells

When rectangular wells are used and solids-bearing stormwater is
anticipated, the preferred approach is to improve handling of sediments
by creating confined pockets for the individual pumps and using steep
slopes of 60 degrees or higher for vertical transitions to the confined
pockets. The solids are then discharged by the main pump(s). Figure 9‑4
shows a recommended rectangular wet well configuration^15^. Minimum
slopes of 60 degrees are based on using concrete. The slopes could be
reduced to 45 degrees if the walls are lined with PVC. The pocket depth
should be a minimum of 2 pump bell diameters (2D). Individual pockets
should be square with sides of 1.5 to 2.0 D length. The pump bowl or
volute should be set D/4 above the floor of the wet well. This
configuration requires a cone under each pump inlet (shown in Figure
9-4). For pump capacities in excess if 0.189 m^3^/s (3000 gpm)
anti-rotation baffles are necessary.

![](media/image66.png){width="3.5416666666666665in"
height="6.0152777777777775in"}

72. []{#__RefHeading___Toc509049976 .anchor}Figure 9‑60. Confined
    rectangular wet well design

    Adapted from reference 15

When using the wet well configuration identified in Figure 9‑4, removal
of settled solids will usually be effected when the pumps are activated.
Floating solids could be removed by each pump if the water level is
allowed to drop so low as to cause a strong vortex. However, each pump
should be run separately. This may not be very practical for a
stormwater pump because the well water level would have to be
replenished after evacuation from the first pump. This would require an
external source of water for flushing.

### Circular Sumps

#### Limitations of Circular Sump Criteria

The Hydraulic Institute recommends use of the circular sump dimension
criteria for individual pump capacities of 0.315 m^3^/s (5000 gpm) or
less. The Hydraulic Institute recommends that model tests be performed
for stations that exceed this limit. If the design exceeds this limit,
the designer should check to see if the pump manufacturer has performed
tests to establish sump criteria. If not, the designer should do one of
the following:

select another manufacturer's pumps with appropriate sump criteria,

use a larger number of smaller capacity pumps,

increase the storage unit size to reduce total pumping requirements,

use a rectangular sump, or

use multiple and separate wet wells.

#### Dimensions for Circular Sumps

Figure 9‑5, Figure 9‑6, and Figure 9‑7 identify the sump dimensions for
various recommended configurations in a circular sump. The dimensions
apply to sumps used for wet-pit stations. Table 9‑3 presents the
Hydraulic Institute criteria for the sump dimensions.

73. []{#__RefHeading___Toc509049865 .anchor}Table 9‑17. Circular sump
    dimensions

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5.  Adapted from reference 15

  ----------- ------------------------------------------- -----------------
  Dimension   Description                                 Recommended Value

  C           Clearance between pump inlet bell and sump  0.3D - 0.5D
              floor                                       

  D           Outside diameter of pump inlet bell/volute  See 8.3.14 Pump
                                                          Bell/Intake
                                                          Diameter

  H~min~      Minimum water depth in sump                 S + C

  S           Minimum pump inlet bell submergence         See Equation 9-1

  C~b~        Minimum clearance between adjacent          Greater of 0.25D
              bells/volutes                               or 100 mm ( 4 in)

  C~w~        Minimum clearance between bell/volute and   Greater of 0.25D
              closest sump wall                           or 100 mm ( 4 in)

  D~s~        Inside diameter of sump                     See Table 9‑4

  D~p~        Diameter of inflow conduit                  Refer to 9.1.5.3
                                                          Inflow Pipe for
                                                          Circular Sump

  L~p~        Unobstructed straight length of inflow      5D~p~
              conduit                                     
  ----------- ------------------------------------------- -----------------

The following table identifies Hydraulic Institute recommendations for
establishing the inside diameter of the sump, D~s~. Refer to Table 9‑3
for a description of variables. All dimensions should be in consistent
units -- i.e. m (ft). The Hydraulic Institute document, Pump Intake
Design^15^, identifies additional configurations.

74. []{#__RefHeading___Toc509049866 .anchor}Table 9‑18. Recommended sump
    inside diameter (D~s~)

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6.  Adapted from reference 15

  ----------------------- ----------------------- ------------------------------------------
  Configuration           Reference Figure        Equation

  Two pumps along sump    Figure 9‑5              $$D_{s} = 2D + 2C_{w} + C_{b}$$
  centerline                                      

  Two pumps offset from   Figure 9‑6              $$D_{s} = 2\text{.}5D + 2C_{w} + C_{b}$$
  sump centerline                                 

  Three pumps along sump  Figure 9‑7              $$D_{s} = 3D + 2C_{w} + 2C_{b}$$
  centerline                                      
  ----------------------- ----------------------- ------------------------------------------

![](media/image67.wmf)

75. []{#__RefHeading___Toc509049977 .anchor}Figure 9‑61. Circular sump
    -- two pumps on center

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7.  Adapted from reference 15

![](media/image68.png){width="5.055555555555555in"
height="6.319444444444445in"}

76. []{#__RefHeading___Toc509049978 .anchor}Figure 9‑62. Circular sump
    -- two pumps off center

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8.  Adapted from reference 15

![](media/image69.png){width="5.000694444444444in"
height="6.263888888888889in"}

77. []{#__RefHeading___Toc509049979 .anchor}Figure 9‑63. Circular sump
    -- three pumps on center

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9.  Adapted from reference 15

#### Inflow Pipe for Circular Sump

It is recommended that the invert of the inflow conduit to the sump be
set at the lowest pumping elevation (minimum water level) in the sump.
This based on the following considerations:

1.  The Hydraulic Institute^15^ recommends that the inflow pipe invert
    not be higher than the lowest pumping level to minimize the
    potential for air entrainment and vortices resulting from free fall
    of the inflow.

2.  If the invert of the inflow pipe is set below the lowest pumping
    level, the volume in the pipe below the pumping level will be
    ineffective with respect to available and usable storage.

The inflow pipe should be radial and perpendicular to the pumps to
minimize rotational flow patterns. Also, the inflow pipe should be clear
of any fixtures or obstacles for a distance of five pipe diameters
upstream of the sump.^15^

The diameter of the pipe should be large enough to ensure that excessive
inflow velocities are not incurred, yet small enough to minimize the
potential for sedimentation. A practical inflow pipe velocity range
appears to be about 0.6 m/s -- 1.2 m/s (2 fps -- 4 fps).

#### Example of Circular Sump Dimensions

It is necessary to establish sump dimensions and clearance values for a
circular wet well in which will be placed two 0.2 m^3^/s (7 cfs) pumps
with bell diameters of 600 mm (2 ft) each. The pumps will be offset from
the centerline. The lowest pump stop elevation (minimum water level in
the sump) is 16.750 m (54.95 ft). The inflow line is a 1.2 m diameter
pipe with a clear and straight length of 160 m. The invert elevation of
the inflow line at the sump is 16.75 m (54.95 ft).

The total pumping capacity is 2 x 0.2 = 0.4 m^3^/s (14 cfs)

The velocity at the bell face is:

$V = \frac{Q}{A}$ = 0.2/(π x 0.6^2^ / 4) = 0.71 m/s (2.3 fps)

Referring to Table 8‑6, the flow per pump is less than 0.315 m^3^/s and
the velocity is between 0.6 and 2.7 m/s. Also, the individual pumping
rate is less than 2.5 m^3^/s (89 cfs) and the total pumping rate is less
than 6.3 m^3^/s (223 cfs). Thus the Hydraulic Institute recommended sump
dimensions apply.

Using Equation 9-1, the required minimum submergence is:

$S = D + \frac{C_{u}Q_{p}}{D^{1\text{.}5}}$ = 0.6 + 0.935 x 0.2 /
0.6^1.5^ = 1.0 m (3.3 ft)

The remaining appropriate variables appear in the following table based
on the criteria in Table 9-3.

  ----------- ------------------------------------------- -----------------
  Dimension   Calculation                                 Magnitude, m (ft)

  C           0.3 x 0.6                                   0.18 (0.6)

  H~min~      1.0 + 0.18                                  1.18 (3.9)

  C~b~        0.25 x 0.6 = 0.15 (\> 0.1 so OK)            0.15 (0.49)

  C~w~        0.25 x 0.6 = 0.15 (\> 0.1 so OK)            0.15 (0.49)

  D~s~        See Table 9‑4: (2.5 x 0.6) +(2 x 0.15) +    1.95 (6.4)
              0.15                                        

  D~p~        Given                                       1.2 (3.9)

  L~p~        5 x 1.2                                     6 (19.7)
  ----------- ------------------------------------------- -----------------

#### Accommodation of Solids-bearing water in Circular Wells.

Circular wells can be designed or retrofitted to improve handling of
sediments by minimizing the horizontal floor space in the sump except in
the immediate area around the pump inlets and steep slopes for vertical
transitions. A minimum slope of 60 degrees should be used for concrete
or cement grout and 45 degrees for PVC-lined slopes. These measures
increase the propensity for the solids to be suspended in the stormwater
to be discharged by the pumps.

The basic well design should be as discussed in 9.1.5.2 Dimensions for
Circular Sumps with modifications as shown in Figure 9‑8.

![](media/image70.png){width="4.553472222222222in"
height="5.597916666666666in"}

78. []{#__RefHeading___Toc509049980 .anchor}Figure 9‑64. Circular well
    with sloping walls and minimized horizontal floor area

    Adapted from reference 15

When using the wet well configuration identified in Figure 9‑8, removal
of settled solids will usually be effected when the first pump is
activated. Floating solids can be removed by the pumps if the water
level is allowed to drop so low as to cause a strong vortex. By
necessity this will be lower than the required submergence, S, for
normal operation and will cause vibration, noise, and high loads on the
impeller. Thus, removal of floating debris should be limited to specific
cleaning cycles that are applied for only short periods. The frequency
and duration of such cleaning will vary from site to site and should be
based on manufacturer's recommendations. The water level in the well
should not be allowed to drop so low that the pump loses prime.

### Wet Well for a Dry-Pit Station

Figure 9‑9 defines the terms for the sump dimensions for the wet well of
a dry-pit station. Refer to Table 9-1 for identification of the
dimensions and recommended criteria.

![](media/image71.png){width="3.777083333333333in"
height="2.152083333333333in"}

79. []{#__RefHeading___Toc509049981 .anchor}Figure 9‑65. Sump dimensions
    for dry pit installation

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10. Adapted from reference 15

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80. 

### Reduced Intake Velocity

If the pump bell/volute velocity is higher than the relevant limits
established in Table 8‑6, the use of an umbrella may be considered.
However, providing an umbrella will not affect the net positive suction
head requirement. A typical umbrella is shown in Figure 9‑10. The
diameter of the umbrella should be selected to provide an area that
results in a recommended velocity of 1.7 m/s (5.5 fps) using the
following equation.

$D = C_{u}\left( \frac{Q}{V} \right)^{0\text{.}5}$ (9-3)

21. 

D = external diameter of umbrella, mm (in)

C~u~ = unit conversion factor, 1128 (13.54)

*Q* = pump capacity, m^3^/hr (gpm)

*V* = design velocity -- recommended as 1.7 m/s (5.5 fps)

![](media/image72.png){width="4.998611111111111in"
height="3.498611111111111in"}

81. []{#__RefHeading___Toc509049982 .anchor}Figure 9‑66. Typical
    umbrella

## System Checks

### Check Storage Volume

The mass curve routing procedure results in a volume that must be stored
for the selected pump capacities and operation levels. The designer must
compare this value with the total volume available below the design
highwater level. The total available storage provided must exceed the
volume required. If not it will be necessary to make one or more of the
following adjustments:

-   Increase the size of the storage unit below the design highwater
    level.

-   Increase the pump size.

-   Adjust the start/stop elevations

In the example used in this manual, the volume determined from the mass
curve routing procedure (Figure 7‑6) was 223 m^3^ (7880 ft^3^).
Referring to Table 6‑2, the total available storage provided at a design
stage of 2 m was 245.3 m^3^ (8668 ft^3^). Thus, sufficient storage was
provided to avoid exceeding the maximum highwater in the wet well for
the design runoff.

### Check Cycling

If initial switching was based on approximate required cycle times,
review the manufacturer's specified minimum cycle times. If the required
times are greater than those used in Step 1 of Trial Switching you have
several options:

-   Select another pump with a lower required cycle time.

-   Increase the storage to increase the cycling time for the
    established switching elevations.

-   Adjust the switching elevations to increase the cycling storage.

-   Employ an alternating switching scheme. For example, one in which
    the last pump off for one sequence becomes the last pump on for the
    next sequence. This is a recommended approach for design.

In the example used in this manual, the start and stop levels were set
based on providing usable volume of at least 30 m^3^ (Refer to 7.2.11
Procedure to Determine Trial Switching), the volume required for a cycle
time of 10 minutes.

###  Check Frequency

Repeat the mass routing procedure using the selected check frequencies.

#### 100-Year Flood

For the 100-year event, check the level to which the system is likely to
flood. It is reasonable to expect the low point in the roadway to be
inundated during the 100-year. However, you should ensure that the 100
year flood levels do not exceed any of the following:

-   FEMA criteria, if applicable,

-   state or local storm drain criteria for check floods, and

-   critical elevations in wet well.

A critical elevation in the wet well would depend on the station type,
but should be an elevation with freeboard, above which flood damage to
any critical element of the pump system would be incurred.

#### Short Return Period

Checking the routing based on a runoff event of shorter return interval
is often more useful than checking for possible short cycling. A
two-year runoff of duration equal to the time of concentration would be
an appropriate check.

## Backup Pumps 

Conformance to the criteria established for minimum number of pumps
reduces the risk of a complete failure but does not necessarily provide
a safety margin for handling the design conditions. It is preferable to
provide an additional pump over what would be required to meet the
design total pumping capacity. Another way to provide backup capacity is
to use significantly larger pumps than required. Generally, the designer
should choose pumps that are slightly larger than required, but it is
not advisable to oversize the pumps because of the higher potential for
fast cycling. If the pumps are oversized, the designer should do a full
evaluation of the performance of the system with the larger pumps.

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# PUMP HOUSE FEATURES

## Introduction

This chapter identifies and discusses major features of a pump house for
a highway stormwater pump station. The pump house protects the pump
control equipment, pump drivers, and ancillary equipment. The primary
features are:

-   ventilation,

-   walkways,

-   ladders or stairs,

-   doors and hatches,

-   cranes and hoists, and

-   utilities.

## Pump House Structure

The pump house is usually rectangular and constructed with masonry.
Figure 10‑1 shows a typical pump house used by Texas Department of
Public Transportation.

![](media/image73.jpeg){width="5.749305555555556in"
height="3.3465277777777778in"}

82. []{#__RefHeading___Toc509049983 .anchor}Figure 10‑67. Typical pump
    house used by Texas DOT

## Ventilation

The need for ventilation is dependent on the pump station features. A
list of ventilation considerations for use in pump station design
follows:

-   The wet well and dry well should be ventilated by an exhaust fan
    that draws air up from the bottom of the wet well in order to ensure
    a safe working environment for maintenance personnel.

-   Where engine-driven pumps or generators are used, ventilation should
    be provided for fans in the pump-engine room that activate
    automatically when low-level vapor is detected.

-   Stairwell ventilation system may consist of both an intake and an
    exhaust system, where each exhaust duct is equipped with a fire
    damper that closes automatically when smoke is detected in the
    engine room or wet well.

-   Natural ventilation for the superstructure of the station can be
    provided by means of louvers and doorway openings. Louvers are more
    suitable than windows for pump station ventilation and louvers also
    discourage vandalism. Cross‑ventilation is necessary for both
    electric motors and gas engines since the former generate heat and
    the latter require air for combustion. Fixed or manually controlled
    louvers suffice for electric motors, but engines should preferably
    blow open upon activation of the engines or have thermo­statically
    controlled exhaust louvers.

-   Submersible pumps do not usually require ventilation for cooling
    because they are cooled by storm water. However, air quality
    requirements will usually warrant suitable ventilation for the wet
    well and pump house.

Figure 10‑1 shows cooling louvers and exhaust vents for diesel
generators. Figure 10‑2 shows louvers used for exhaust and cooling on a
pump house used by Arizona DOT.

![](media/image74.jpeg){width="5.7652777777777775in"
height="3.2777777777777777in"}

83. []{#__RefHeading___Toc509049984 .anchor}Figure 10‑68. Ventilation on
    Arizona DOT pump house

## Walkways

Catwalks or walkways should be provided where necessary to ensure safe
access to station components.

## Stairways and Ladders

Stairways are preferred to ladders, since ladders are generally more
hazardous, especially when tools or equipment are being carried.

If provided, the stairway from the pump pit to the engine room or pump
room can be enclosed and a bulkhead provided with a gas‑tight door that
is fitted with a gasket. The gasket seals off the pump pit and prevents
gasoline or other explosive vapors from entering the superstructure.
Marine‑type bulkhead doors are sometimes used, but their high threshold,
restricted opening and screw clamps are inconvenient.

## Doors and Hatches

Personnel doors should be provided at each end of the pump room for easy
exit. A wide roll‑up door may be used for equipment and truck access.
Access hatches to the pump pits, when open, must be protected by posts
and surrounding chains. Similar provisions for guard posts and chains
should be made at all other removable cover plates.

## Cranes and Hoists

### Overhead Cranes

Use of large pumps may warrant installation of a permanent lifting
device such as an overhead crane, monorails, jibs or hoists. Figure 10‑3
shows a permanent overhead crane installation with submersible pumps
used by Arizona DOT.

Overhead cranes have three directions of movement that must be
considered in the design of the station:

-   longitudinal, for the bridge,

-   transversely, for the trolley, and

-   vertically, for the hoist.

The top‑riding bridge‑cranes with the end carriages on top of rails set
on longitudinal girders are preferred to the underhanging type of crane,
for which the bridge is hung from the longitudinal beams set below the
roof slab or elsewhere in the structure. The type of crane selected,
however, is primarily dependent upon the ability of the crane to handle
the largest and heaviest predicted load.

![](media/image75.jpeg){width="4.692361111111111in"
height="2.763888888888889in"}

84. []{#__RefHeading___Toc509049985 .anchor}Figure 10‑69. Overhead crane
    over wet well with submersible pumps

### Monorails

The travel path of the hoist is limited to one plane only along a
monorail. The monorail system may be designed to accommodate any portion
of the total weight of equipment with suitable safety factors.

The hoist may travel on a monorail by a hand racking system or may be
electrically powered. The hoist should be electric motor operated by a
pendant control or by a push button station located at a central
location within the building. Power to the hoist is usually provided by
a reeling cable or tag line. The hook should be mounted in a thrust
bearing so that it may be rotated under rated load. The hoist should
have a right and left hand grooved drum to avoid twisting of the block.

### Jib-Cranes

Jib‑cranes have limited use for handling mechanical equipment in a pump
station. They have a horizontal arm pivoted at one end to allow it to
swing. A hoist, electric or manually‑powered, can be positioned as
required along the horizontal arm. Jib-cranes are of most value in trash
handling.

### Hoists

Most hoists used in pumping stations are powered electrically for the
lifting operation and may be suspended from trolleys that are then
either manually or electrically operated.

Hoists should be provided in all stations for the handling of equipment
and materials that cannot be lifted or removed easily from the station
by manual labor. Hoists should be placed over basket screens,
submersible pumps, other pumps or motors and other locations where it is
necessary to lift heavy pieces of machinery or equipment. Where a pump
pit is very deep it may be necessary to have the hoist fitted with cable
drums which are larger than standard, in order to accom­modate the extra
length of cable.

The hoisting anchors are usually embedded in walls or overhead concrete,
which enables rigging to be secured any time dismantling or removal of
pumps is required.

## OSHA Requirements

The Occupational Safety and Health Administration (OSHA) establishes
requirements for features such as those described above. All aspects of
pump station design must comply with current OSHA criteria.
Additionally, there may be stricter state or local criteria that should
be considered.

## Fire Precautions

### Small, Unattended Stations

Small pump station houses constructed entirely with non‑combustible
materials and having small electrically­ powered pumps with means of
immediate egress generally do not require special fire protection
equipment. Not even a chemical fire­ extinguisher is required since any
electrical fire would probably occur while the station was unattended.
Although this would be damaging to equipment, it would not be hazardous
to personnel.

### Large Stations

The pumping equipment at larger pumping stations is typically more
complex, and lubricating oil may be spilled. In such cases, chemical
fire extinguishers should be provided and there should be doors at
opposite ends of the building, equipped with panic bars. All fire
protection provisions should be in accordance with state and local fire
ordinances.

## Security and Safety

The security and safety features of the pump house should maintain a
secure and safe working environment by paying particular attention to
the safety features involved in the operation and maintenance of the
station. For a list of pump station safety features, refer to Chapter
12 - Construction, Operation and Maintenance.

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# BASIC ELECTRICAL AND MECHANICAL INFORMATION

## Introduction

The intent of this manual is to provide detailed guidance for the
hydraulic design of pump stations. This chapter provides
familiarity-level discussion for civil engineers so that the civil
engineer can be make accommodations for other pump station needs and be
conversant with engineers of other disciplines.

## Power Supply

Requirements for pump stations include the power necessary to operate
the pumps and the power required to operate other station components
such as the pump switching, water level sensing, and lighting. Common
power sources for stormwater pump stations include:

-   public utility electricity,

-   electric generators powered by natural gas and diesel, etc., and

-   diesel, natural gas, or liquid propane engines.

### Electrical Mains

#### Supply Lines

Electrical supply from a public utility company is the most common
primary source of power for a stormwater pump station. The reasons
underground electric service is preferred include:

-   the reduced risk resulting from weather-related damage,

-   lower visual impact, and

-   reduction of potential hazards to cranes and other tall mobile
    equipment.

Even if the supply power lines are overhead, it is often practicable and
desirable to tap into the lines at the station right-of-way boundary and
provide underground conduit to the station.

If overhead lines are the only practicable means of providing power to
the station, it is imperative that the power lines be kept clear of the
driveway, station loading area, and turnaround area. Additionally, clear
warning signs should be posted.

#### Electricity Rates

The quality of electrical service will depend on how well the system
maintains a constant voltage under varying load demands and its
susceptibility to outage, especially during storms. Therefore, a
secondary source of electricity is desirable. Where practicable, this
can be an alternate mains supply.

Utility companies are now deregulated and competition may affect rate
schedules. The rates may also vary with a wide array of factors
including:

-   load demand,

-   energy consumption,

-   power factor,

-   available voltages,

-   primary service cost,

-   transformer and substation ownership,

-   fuel cost, and

-   demand interval.

Estimates of the load data and potential demand for initial and future
requirements of the pump station will be needed to evaluate potential
costs.

### Power from Generators

In remote areas, generators may be the primary source of power. When
generators and engines are used, several fuel options exist. Natural gas
can be piped underground to the station by a public utility, but such
service is usually available only in urban areas. Liquid propane gas and
diesel can be stored on site, such as is shown in Figure 11‑1. Proper
access for supply vehicles must be maintained, with all locations of
storage above any flood hazard. The choice of engine type and fuel type
is usually based on power requirements, availability and economics. In
EPA non-attainment areas for air quality, use of natural gas may be
preferable to diesel. Fuel storage areas must be designed to contain
spills at the site.

![](media/image76.jpeg){width="4.470138888888889in"
height="2.834722222222222in"}

[]{#__RefHeading___Toc509049986 .anchor}Figure 11‑70. Liquid propane
tanks for pump station power

### Power Use

If electric motors are used the following table provides
recommendations.

[]{#__RefHeading___Toc509049867 .anchor}Table 11‑19. Recommendations for
power use

  ----------------------------------- -----------------------------------
  Item                                Preferred Criterion

  Motor Type                          Constant speed, 3-phase induction

  Motor Voltage                       440 V - 575 V

  Maximum Power Rating                225 kW (300 hp)

  Max Power when using portable       56 kW (75 hp)
  backup power                        
  ----------------------------------- -----------------------------------

### Electrical Power Factor

When an AC electric motor is running, the cycles of voltage and current
may be out of phase with each other, so that the product of voltage and
current, called apparent power, will be greater than the actual power
consumed by the circuit. The ratio of actual power consumed by a circuit
to the apparent power of that circuit is called the power factor. Power
factor is expressed as a number usually between 0.8 and 1.0. As high a
power factor as possible is desired because this is one of the items
considered by the serving utility in determining its billing to the
user. There is a cost penalty for low power factor. Capacitors are
sometimes used in a circuit to improve power factor.

## Motors

Electric motors account for a high percentage of all pump drivers.
Figure 11‑2 shows a typical motor for a vertical pump. Alternating
current (AC) electric motors are the most frequently used drivers in
pumping stations primarily because of their versatility, compactness,
low maintenance and reliability.

![](media/image77.jpeg){width="3.959722222222222in"
height="2.542361111111111in"}

[]{#__RefHeading___Toc509049987 .anchor}Figure 11‑71. Typical electric
motors for vertical pumps

The three most common types of AC electric motors used to drive pumps
are: ^1^

squirrel-cage induction,

synchronous, and

wound rotor-motors.

Squirrel-cage induction motors are by far the most common motors used to
drive pumps and generally operate at a single speed. Synchronous motors
are similar to squirrel-cage induction motors except that they operate
at speeds which are determined by the supply electrical frequency.
Synchronous motors are used for pump applications requiring larger
horsepower ratings at lower speed conditions. Wound-rotor induction
motors are similar to squirrel-cage but can be used either where torque
control is required or where variable speed is necessary. Variable speed
motors are not preferred for use with highway stormwater pumps.

### Other Motors

Other AC motors include the brushless synchronous motor; the
water-cooled motor, which is typically quieter than air-cooled motors;
and the low inrush current motor, which, along with the water-cooled
motor, is generally preferred for pumping applications requiring higher
power.

Direct current (DC) motors are only occasionally used in pumping
stations and are used only when DC is the only power available.

### Service Factor

Service factor is essentially a safety margin that refers to the
motor\'s ability to continuously deliver horsepower beyond its nameplate
rating under specified conditions. Motors are designed with an allowable
rise in temperature above ambient temperature during operation. The
maximum allowable temperature rise during operation for a motor varies
with respect to insulation class and the motor\'s service factor. Most
motors are rated with a 1.0 or 1.15 service factor. A 10 kW (13.3 hp)
motor operating under rated conditions with a 1.15 service factor should
be able to continuously deliver 11.5 kW (15.3 hp) without exceeding the
NEMA allowable temperature rise for its insulation system. NEMA allows
an ambient temperature of 40 C (104 F) when specifying \"usual service
conditions.\"

If the ambient temperature exceeds 40 C or at elevations above 1005 m
(3,300 feet), the motor service factor must be reduced or a higher
horsepower motor is required. As the oversized motor will be
underloaded, the operating temperature rise is less and overheating will
be reduced.

### Motor Starting

During starting, the electric motor draws a high current that can be as
much as ten times the normal operating current. The current surge incurs
voltage drops and electromagnetic interference that can affect the
electrical distribution system. Power companies or municipal agencies
usually establish limits on the magnitude of current surges. Several
wiring methods, such as the following, may be used to start the motors:

-   across the line

-   automatic transformer

-   wye-delta

-   electronic

"Across the line" does not provide voltage control. The latter three
systems control current surges by reducing the starting voltage. The
reduced starting voltage is accompanied by reduced starting torque for
the motors. The electrical designer must ensure that the starting
voltage provides enough torque to the desired starting motors.

#### Across the line

If the motors for pumps require a lower surge current than specified
limits, the normal "across the line" starting method can be used in
which the motors are directly wired to the power distribution system.

#### Automatic Transformer

One of the most common and preferred starting methods is the use of
three automatic transformers which reduce starting voltage for a
specific period of time then revert control to across the line. Typical
automatic transformers allow connections for voltage reductions of 50%,
60%, and 80%.

#### Wye-delta

This is a complex connection that is usually used with specific motors
that have six-lead wiring. Typically, there is a fixed voltage reduction
of about 58%.

#### Electronic

Electronic switches known as thyristors can be set to vary the voltage
gradually during starting to ensure that the current surge does not
exceed a specified limit. Though, seemingly they would be preferred
because of the degree of control, they are usually more expensive than
other starting methods.

#### Implications of Starting Methods

For the hydraulic designer, it may be necessary to consider the length
of time it is likely to take for the pumps to reach operating speed and
to check that there is sufficient storage available to accommodate the
additional inflow during start-up time. However, if the appropriate
cycling volume is provided, potential lag times should not usually be a
significant issue.

### Advantages of Using Electric Motors

The advantages of using electric motors for driving stormwater pumps are
as follows:

-   they are compact and have minimum space requirements,

-   installation is usually less expensive than for engines,

-   they are generally easy to remove for maintenance or replacement,

-   they are available in a variety of sizes,

-   various insulation systems are available, and

-   numerous mounting and enclosure configurations are available.

### Disadvantages of Using Electric Motors

The disadvantages of using electric motors for driving stormwater pumps
are as follows:

-   they are susceptible to damage by flooding,

-   high starting currents are required for most types,

-   they are subject to utility outages,

-   an alternate power source will be required for the system,

-   space is required for control equipment,

-   expensive and complex control systems are required for some types,

-   they are subject to overheating, and

-   they may be more expensive to operate than engines.

## Engines

Engines are used only sparingly as pump drivers in small pump stations.
Engines are usually considered inferior to electric motors for these
stations because of the noise and vibrations they produce, the space
they occupy, and the maintenance and operating supervision required.
Figure 11‑3 shows an engine that drives a vertical pump using a right
angle gear. The use of engines should be considered if the power supply
is unreliable or expensive and the environmental problems appear
insurmountable. Engines are used more commonly in large pump stations.

![](media/image78.jpeg){width="2.9583333333333335in"
height="4.595138888888889in"}

[]{#__RefHeading___Toc509049988 .anchor}Figure 11‑72. Engine drive

### Engine Categories

Engines that might be used to drive pumps in pumping stations can be
grouped according to three characteristics:

ignition,

cycle, and

configuration.

Engines based upon ignition can be subdivided into those using spark
ignition and compression ignition. Engines using spark ignition require
a spark to ignite the fuel. In compression ignition engines, the heat
generated by the compression of the fuel-air mixture ignites the fuel.

Two and four-stroke cycle designs are available for stationary engines.
The two-stroke cycle engine generally is limited to compression ignition
designs and is less efficient, more complex, lighter in weight, less
expensive, and noisier than four-stroke cycle engines. Four-stroke cycle
engines are available as both spark ignition and compression ignition
types.

In-line and V-block configurations are available for stationary engines.
V-type engines are generally more expensive to maintain, smoother
operating, more compact, and require less floor space than in-line
engines.

### Advantages of Using Engines

The advantages of selecting an engine over an electric motor include:

-   greater reliability,

-   economy of operation,

-   improved protection against surge damage, and

-   the ability to be placed in remote locations or where electrical
    supply is unreliable.

### Disadvantages of Using Engines

The disadvantages of selecting an engine over an electric motor include:

-   concern over noise emissions,

-   concern over air pollutant emissions,

-   lack of adequate maintenance capability, and

-   high capital cost.

## Backup Power

Where electrically driven pumps are used, an alternate source of
electricity is essential unless an inoperative pump station can be
tolerated during a storm. The choice of backup is usually based on
economics.

### Alternate Sources of Electrical Power

Alternate sources of electrical power, in case the service from the
utility company is interrupted, include:

-   a dual power supply with automatic transfer,

-   a dual power supply with interlocking circuit breakers,

-   permanent back-up generators, and

-   mobile generator, manual transfer switch, and standby power (SBP)
    receptacle.

Figure 11‑4 shows a diesel-powered generator used by Texas DOT as a
standard feature of their stations in Houston. Primary power is at high
risk for interruption during the frequent thunderstorms that are
experienced in Houston. There is usually a short time delay while the
backup power is engaged. Preferably, there should be a safety margin of
storage volume in the system to accommodate the design runoff volume
that would occur during the time delay.

![](media/image79.png){width="4.971527777777778in"
height="3.3895833333333334in"}

85. []{#__RefHeading___Toc509049989 .anchor}Figure 11‑73. Diesel-powered
    backup generator

The maximum power rating of available mobile generators will limit the
power rating for the pump motors. Figure 11‑5 shows a mobile generator
and SBP used by Caltrans. Caltrans limits the main pump ratings to about
56 kW (75 HP) to be compatible with the mobile generators. If the local
preference is to use mobile generators, the designer should consider the
average response time for providing the mobile power. The storage system
should be sized such that the design volume of rainfall during the
response time interval can be held without exceeding the maximum
highwater elevation.

![](media/image80.jpeg){width="3.970833333333333in"
height="2.542361111111111in"}

86. []{#__RefHeading___Toc509049990 .anchor}Figure 11‑74. Mobile
    generator and standby power receptacle

### Backup Engines

Dual-drive pumps are a viable alternative for most dry-pit stations and
some wet-pit stations that use vertical pumps. The electric motor is
usually the primary driver and is placed on the main axis of the pump
drive shaft. The engine drives a shaft that is connected to the main
shaft via a right angle gear drive and clutch.

## Electrical Systems

Primary electrical systems that should be considered in the design of a
pump station include systems that:

-   provide surge protection for pump station equipment during
    electrical service irregularities or failures from the utility
    company,

-   provides for phase failure,

-   provides protection against lightening strikes,

-   provide automatic power transfer, and

-   allow the standby engines to start automatically in response to
    sensing a power outage and a change in water level in the wet well,
    since most pumping stations are unattended.

### Protection Systems

A switching system should minimize damage to the pumps and limit the
extent and duration of interruptions in the electrical service supplied
to the station. A system must isolate any affected portion of a station
system while maintaining normal service for the rest of the system. It
must minimize the danger of short‑circuit currents and may provide
alternate circuits to minimize the duration and extent of outages.

System protection is provided by the following devices:

-   a fuse, which is the simplest of all protective devices, performing
    both sensing and interrupting functions.

-   circuit breakers, which are interrupting devices and must be used in
    conjunction with sensing devices to fulfill the detection function.
    Most low‑voltage applications use either molded‑case circuit
    breakers or other low‑voltage circuit breakers having series sensing
    devices built into the equipment.

Circuit breakers and fuses are employed to disconnect the affected parts
of the power system. The use of computer-controlled circuitry to perform
the sensing and timing functions can help optimize control conditions
and allow for easier testing, monitoring and adjustments.

When two utility sources from separate supply sources and over separate
lines are connected, an automatic transfer switch is usually located in
the main distribution equipment. Special consideration should be given
to the ability of the switch to:

-   close against high inrush currents,

-   carry full rated current continuously from normal and secondary
    source,

-   withstand fault currents without contact separation, and

-   have adequate interrupting capacity.

### Engine and Motor Switches

Since most pumping stations are unattended, engines must start
automatically. The engines are designed to start at a predetermined low
speed or load. After a suitable time delay the throttle is opened to its
operating speed. A selector switch is included on the control panel.

During a power outage, a transfer switch should be provided with an
accessory control with switches that disconnect the main pump motors
during the energized condition, prior to transfer, and reconnect them
after transfer when the residual voltage has been substantially reduced.
A time delay of 2 to 10 minutes should be provided to prevent transfer
back to normal source when normal service is recovered after an outage.

### Water Level Sensors

The various types of pump control sensors, which regulate pump activity,
include:

-   Float switch

-   Electrode probes

-   Ultrasonic devices

-   Tilting bulb with mercury switch

-   Bubble-tube

-   Entrapped air pressure switch

#### Float Switch

A float switch consists of a floating device attached to a moving tape
or wire and pulley system. The float rises and falls with the water
level in the sump. When the water level reaches a given height, the
pumps are activated by a control switch and the pumps continue pumping
water from the intake area until the water level drops. One particular
specification of which the hydraulic designer should be aware is that
float switches should not be used if the number of pump cycles is
expected to exceed 4 per hour because they are typically relatively slow
to respond. Also, the float will respond to fluctuations caused by
turbulence in the sump. Thus designers will usually ensure that a
minimum height of about 150 mm (6 inches) is used between successive
start elevations of pumps and successive stop elevations of pumps.

#### Electrodes

Electrode probes are activated when the rise in water level causes an
electric current to pass between the electrodes of the sensor thereby
activating the pumps. The electrodes are suspended vertically from the
top of the pit with their lower ends positioned at the level elevations
at which the control device is to be actuated. These sensors can tend to
corrode and can be fouled by floating debris and pollutants.

#### Ultrasonic Transducers

Ultrasonic devices emit a mechanical pulse that registers a change in
the water level in the intake box. The sensor registers a change in
frequency due to the rise in water level and the pump controls detect
this change and activate the pumps.

#### Mercury Switch

A tilting bulb with mercury switch (Figure 11‑6) registers a change in
the orientation of the liquid mercury within the bulb caused by a change
in the water level in the intake box. This type requires a significant
change in level to open or close. Thus, the designer will usually apply
a water level change of at least 150 mm (6 in.) between successive pump
start elevations and between successive pump stop elevations.

![](media/image81.jpeg){width="3.7909722222222224in"
height="2.667361111111111in"}

[]{#__RefHeading___Toc509049991 .anchor}Figure 11‑75. Tilting bulb
switch

#### Bubble Tube

A bubble tube regulates pump activity by registering a change in the
orientation of the bubble within the bubble-tube caused by a change in
the water level. A bubble-tube is placed inside a conduit installed
between the wet well and dry well of dry-pit stations. The tube enters
the wet well from the top and terminates in the dry well at an elevation
above the highest possible water elevation. When the wet well and the
dry well do not have a common wall then a bubble tube presents the best
alternative.

#### Air Pressure Switch

The switch registers an increase in pressure due to the compression of
the air in the inflow pipe resulting from an increase in the height of
water in the wet well. When the water level reaches a given height and
corresponding air pressure the switch is activated and the pump starts.
When the water level drops, the switch closes and the pump stops.

### Sensing and Alarm Systems

Sensors are provided for critical operating systems within the pumping
station in order to detect changes in standard operating procedure. One
such system is the gas detection system. Wet-pit stations with a large,
closed, rectangular pump pit, require fuel presence alarms. Stations
with a ventilated below-pavement storage unit, such as the dry-pit
station, do not require a gas detection system.

Detection and alarm systems are typically used for:

-   gas detection,

-   heat detection,

-   pump failure,

-   pump usage monitoring,

-   indicating high water, and

-   electrical failure.

Information from the sensor (detector) can be made available at a remote
point by telemetry.

## Mechanical Considerations

### Mechanical Packing

Packing is the term given to the materials used to control air and water
leakage between the pump impeller casing and the dry side of the drive
shaft casing. A natural or synthetic woven fabric is used. Since the
shaft rotates in a fixed casing, the woven fabric must be lubricated.
Typical packing materials include:

-   flax,

-   cotton,

-   jute,

-   graphite,

-   rayon,

-   carbon,

-   metal strands or foils, and

-   a variety of synthetics including Teflon^TM^, TFE^TM^, and
    Kevlar^TM^.

Lubricants include:

-   grease,

-   graphite,

-   oils,

-   mica,

-   silicone, and

-   other synthetics.

The packing is usually selected by the pump manufacturer as part of the
pump design or the project's mechanical designer. However, selection of
the appropriate packing should be based on factors such as:

-   pump operating pressure,

-   shaft speed, and

-   water temperature.

The designer will need to establish this information and relay it to
whoever will select the packing.

### Minimizing Motor Wear, Tear, and Overheating

A first consideration for minimizing potential problems is to keep the
pump system as simple as possible. Submersible pumps are a popular
choice because they are self contained and do not require long drive
shafts and other couplings.

Motor wear, tear, and overheating can be minimized by reducing the
friction between the moving parts within a mechanical system using
adequate lubrication. Overheating may be a concern for:

anti-friction bearings. These may present a problem of overheating when
too much lubricant (grease) is used, which causes the turning action of
the rolling element to produce excessive fluid friction.

insulation windings. Damage to the insulation windings is the principal
cause of engine failure.

the starting motor, since the starting current can be as high as ten
times the full-load operating current. Each start temporarily overheats
the motor insulation, and the life of the motor is reduced by the number
of starts. Normal motor overload protective relays will not protect a
motor against damage from too many successive starts, so it is necessary
to limit the number of starts over a given period of time. If the motor
can come up to speed with little or no load, the heating effect is much
less.

#### Bearings and Seals

Motor bearings, which are either plain or anti-friction, support and
control the motion of a rotating shaft.

Plain bearings are either sleeve or thrust types that depend on a
lubricating film to reduce friction between the shaft and the bearing.
When properly designed and lubricated, plain bearings develop oil films
that have tremendous load‑carrying capabili­ties.

Anti-friction bearings operate on the principle of rolling contact
between elastic circular bodies. The resistance of this rolling action
is quite low. At low speeds, ball and roller bearings develop so little
resistance through rolling that they are superior to plain bearings.
Individual anti-­friction bearings can support, at the same time, both
radial and thrust loads in varying degrees ‑‑ a characteristic not
typical of plain bearings.

The following information may be of assistance in the consideration and
selection of bearings and seals for inclusion in the pump station
design:

The life of ball or roller bearings depends on fatigue strength of the
material and decreases as speed and load increases.

Rotating seals and other mechanical and chemical devices help protect
against unfavorable environmental condi­tions, such as vibration, poor
fits, corrosion or abrasive dirt.

Normally standard horizontal motors up through 93 kW (125 horsepower),
1800 rpm, are furnished with radial deep‑groove ball bearings which
permit the motor to be mounted in any position, including vertical,
providing the downward thrust on the shaft is less than the weight of
the motor.

Both ball and roller, as well as sliding element‑type, are used to carry
the weight of the motor rotating element and in some cases the weight of
the pump shaft and impeller.

#### Lubrication

Lubrication provides the means whereby all the mechanical parts within a
mechanical system may be kept moving and operating efficiently.
Anti-friction bearings, which are relatively insensitive to viscosity
changes, require only small amounts of lubrication. All vertical motors
of 75 kW (100 horsepower) and over should have the thrust bearing and
lower guide bearing oil lubricated, with visible means for checking oil
level and quality. Motors below 75 kW (100 horsepower) may be grease
lubricated, but the system must provide for flushing out and replacing
old grease.

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#  {#section-4 .unnumbered}

# CONSTRUCTION, OPERATION AND MAINTENANCE

## Introduction

This chapter contains suggestions that should be considered by those
responsible for the design, construction, operation and maintenance of
highway stormwater pump stations.

## Construction

### Safety

Safety during construction includes:

-   providing adequate workspace with buffer zones,

-   providing traffic control during construction, which conforms to
    National or State manuals on uniform traffic control devices,

-   maintaining stringent security to minimize the potential for
    vandalism and the injury of intruders, especially children.

### Temporary Sediment Control

The designer should establish appropriate sediment and pollution control
measures that the contractor must adhere to during construction. The
primary criteria are the National Pollution and Discharge Elimination
System (NPDES) permit requirements for industrial activities. The
designer and contractor should make themselves familiar with the
pertinent best management practices and notice of intent (NOI)
procedures applicable in the particular state.

Even if disturbed areas are smaller than those established by NPDES
criteria, currently 2 ha (5 acres), the designer should adopt the most
practicable best management practices for the site conditions. Excessive
sediment loads can overload the pump system, possibly causing premature
failure. Therefore, in addition to typical perimeter controls, it is not
excessive to consider temporary measures such as:

-   sediment traps,

-   sedimentation basins, and

-   diversion berms.

Refer to the FHWA publication, *Urban Drainage Design Manual, Chapter
10*, ^10^ for a discussion on various measures. The control measures
should be inspected frequently, especially after any rainfall that
results in significant runoff.

### Contract Issues

It is recommended that the highway agency does not accept ownership of
the pump station until all of the following conditions have been met:

-   construction of the entire pump station is complete,

-   construction of all stages of construction that drain to the pump
    station are complete, and

-   the pump station components have been field tested.

The pump station is likely to be used to drain the work site during
staged construction. In addition to handling normal runoff, the pump
station can be subjected to temporary excessive and destructive sediment
and debris loads that may emanate from the construction site. Measures
to limit sedimentation (discussed in Section 12.2.2 - Temporary Sediment
Control) should be established and maintained throughout the
construction. Testing is discussed in Section 12.3 - Pump Station
Testing.

### Architecture

Pump station architecture is usually only thought of in terms of visual
appearance, which varies greatly from one area to another depending upon
any prevailing architectural standards of the agency, station location
and other factors. Interior arrangements of space should accommodate
necessary pumping machinery, mechanical appurtenances and other pump
station features including the minimal space and facilities required for
safe access, safe working areas and the convenience of personnel.

### Aesthetics

The aesthetic value of the pump house structure and the suitability of
the design to its surroundings is becoming an increasingly important
part of the pump station design process. The choice of materials for the
pump station superstructure can enhance the aesthetic value of the
structure.

The use of masonry may provide pleasing results. The masonry will
usually be either brick or concrete block, although natural stone may be
used, either as a solid wall or a veneer. A face brick of some type is
usually aesthetically pleasing, with or without exposed concrete
columns, beams or other features. Concrete block masonry is usually
preferred over brick due to the greater variety of block type and size
available.

### Construction Materials

Reinforced concrete is the usual choice for the substructure of a pump
station, but the method of placement varies. Cast-in‑place construction
is usually used for rectangular pump pits. Precast concrete units, which
are normally fabricated either at the site or elsewhere and then sunk to
the required level, are usually in the form of circular caissons.
Cast‑iron or pressed steel rings can be used for caisson‑type stations.
Precast or cast-in-place concrete is usually the most suitable material
for stormwater pump station substructures.

### Pump Well Requirements

When vertical pumps are used, each pump must be set in the wet well and
its motor driver or its gear‑head, if engine driven, must be above the
pump room floor. For submersible and vertical pumps, an opening in the
floor is required to permit removal of the pump and associated fixtures.

For submersible and horizontal pumps, the pump/motor must be securely
attached to the concrete floor using a baseplate assembly. The baseplate
should be securely embedded in the top of the concrete floor. Pump base
plates are normally quite thick and the anchor bolts should be recessed
to avoid the hazard of personnel tripping. Tripping hazards from
electrical conduit stub‑ups and runs or from plumbing and piping runs
must be avoided throughout the pump room.

### Access to Pump Equipment

The stormwater pump station house is an enclosing structure and must
provide access to the pumps and other equipment. The enclosure must have
doors, roof hatches, or covered openings through which equipment can be
passed or debris can be removed with a mobile crane. Enough room should
be incorporated into the planning and design of a pump station for the
operation of the crane and hoist and removal of the pumps and heavy
equipment.

### Lifting Devices

Provision must be made in the design of a pump station for handling
pumps and other equipment. For large pumps, a common approach is to use
overhead, power‑operated, bridge‑cranes with lay‑down or work‑areas on
the pump room floor where equipment can be dismantled or repaired. A
more cost-effective alternative, however, is to provide simple
hand‑chain lifting devices or to use mobile cranes or hoists to remove
equipment from the pump station for repair at a central location.

## Pump Station Testing

Pumps are subjected to numerous performance tests including factory
tests and model tests in order to ensure correct pump operation.

Field testing should take place after the pumps have been installed at
the station, prior to being accepted. Testing should:

-   ensure correct operation of pumps,

-   ensure operating efficiency of the station,

-   check power supply,

-   check pump performance, and

-   check alarm system.

### Preliminary Considerations

The accuracy and reliability of any field testing depends on:

-   pump installation, which should be performed with the field testing
    specifically in mind so as to provide for the use of suitable
    calibrated instrumentation,

-   reliable and precise instrumentation,

-   proper installation of instrumentation, and

-   responsible and qualified technical personnel to perform the
    testing.

### Preliminary Testing

Instrument accuracy and reliability needs to be assured before
proceeding with testing. The ability of the personnel assigned to
perform the testing also should be assessed. A number of preliminary
tests may be necessary to ensure that the recorded data is accurate and
reliable.

Accurate and reliable data should fall within tolerances and
fluctuations specified by the manufacturer and/or Hydraulic Institute
Standards. Preliminary testing is performed to determine the following
quantities:

-   head differential across pump,

-   discharge,

-   suction,

-   speed, and

-   power input to pump.

Test tolerances for pumps, with respect to capacity, total head, or
efficiency at the rated or specified conditions, require no negative
tolerance or margin. Conformity with one of the following tolerances is
required.

-   At rated total dynamic head: +10% of rated capacity

-   At rated capacity: +5% of rated total dynamic head under 150-m (450
    ft.)

+3% of rated total dynamic head 150-m and over.

### Testing

#### Pump Performance Tests

Pump performance tests should be made preferably at the maximum,
average, and minimum total dynamic heads specified by the designer. The
required test information for pump performance tests typically includes
the following:

#### General

The pump tester should document the following information before each
test is carried out:

-   date,

-   location,

-   test number,

-   name of person performing test, and

-   pump identification number, if applicable.

#### Head

The following head determinations are made to check conformance:

-   head at standard atmospheric pressure,

-   gauge head, and

-   total dynamic heads (maximum, average and minimum).

#### Capacity

The capacity test includes determining:

-   volume of the storage unit, and

-   rate of flow (volume/test period).

#### Power

The following quantities are required for each of the pumps in
combination:

-   volts (unloaded),

-   volts (loaded),

-   measured current,

-   100% full load current,

-   adjustment factor, and

-   adjustment current.

#### Performance Curves

Pump performance is a function of the following quantities:

-   total dynamic head,

-   brake power,

-   net positive suction head, and

-   derived pump efficiency.

The performance tests that determine these quantities are typically
carried out over a range of flows at constant speed.

#### Inspection Tests

Visual inspection of the pumps is part of the testing procedure and is
necessary prior to testing to ensure the proper orientation of the pump.
The following are included usually in the inspection:

-   alignment of pump and driver,

-   direction of rotation,

-   electrical connections,

-   operation of stuffing boxes and lubrication systems, and

-   wearing ring clearance.

#### Hydrostatic Tests

These tests are normally carried out by the pump manufacturer prior to
pump installation. Each part of the pump should be capable of
withstanding a hydrostatic test at test pressures that should be
maintained for at least five minutes, at not less than the greater of
the following:

-   150% of the pressure that occurs in the pump when operating at rated
    conditions, or

-   125% of the pressure that occurs in the pump when operating at rated
    conditions, but with the pump discharge valve closed.

## Operation And Maintenance

### General Considerations

The designer of a stormwater pump station should pay careful attention
to the affect that design features have on operation and maintenance.
The design should facilitate and minimize the cost of operation and
maintenance without adding unreasonably to construction costs. The
design also should minimize the possibility of malfunctions and stations
becoming inoperable.

Primary design considerations or measures to help minimize operation and
maintenance costs include:

-   ensuring proper hydraulic design,

-   providing for debris trapping and removal,

-   providing for sediment handling or control and removal,

-   considering appropriate pump type for given conditions,

-   accounting for the experience of local maintenance personnel, and

-   maintaining consistency with existing maintenance capabilities.

### Safety

All elements of the pump station should be thoroughly reviewed for
safety during operation and maintenance. Particular attention should be
given to all safety features in order to maintain a safe working
environment. All safety features included in the design and construction
of pumping stations must be in accordance with the prescribed local,
state and national safety laws and codes. Safety features include:

-   ladders, stairwells, railings and other access points for use by
    maintenance and operations personnel in accordance with OSHA and
    local standards,

-   guards and railings placed around all access holes and openings and
    all mechanical equipment with which the operator might come into
    contact including belt drives, gears, chain drives, rotating drive
    shafts and other moving parts,

-   adequate space for the operation and maintenance of all equipment,

-   warning signs near dangerous machinery and safety rules posted in
    appropriate locations throughout the station,

-   paying particular attention to providing proper and reliable
    lighting especially when there is moving equipment,

-   rubber mats provided in front of all electrical equipment where
    there is a possibility of electric shock,

-   electrical equipment properly insulated and grounded,

-   switches and controls of the non-sparking type,

-   proper drainage to eliminate the possibility of slippery surfaces,

-   a telephone to permit an operator to maintain regular contact with
    the main office,

-   air testing and monitoring equipment in order to assure a safe
    environment within the station,

-   ventilation systems to minimize the dangers of explosions and those
    arising from pollutants,

-   fire extinguishers throughout the station in case of emergency,

-   permanent traffic warning signs, and

-   temporary traffic control, if access is limited.

An entry plan should be developed as part of the operation and
maintenance procedures for each pump station. The plan should identify
measures to be taken prior to and during any visit to the pump station,
including monitoring of environmental conditions, especially air
quality. All measures should conform with current OSHA requirements.

### Access to the Pump Station Site

Personnel safety is a paramount concern, so access should not interfere
with vehicular traffic. If right-of-way or other physical restrictions
preclude construction of a dedicated service road or driveway, temporary
barricades and signs should be placed during inspection and maintenance
in conformance with the *National Manual for Uniform Traffic Control
Devices*.^14^

### Removal of Collected Debris and Sediment

Normal operation of the collection system will result in a build up of
debris on trash racks, gratings and screens and sediment in the storage
unit and sump. The build-up of debris may cause the bearings, impellers
and bowls to be damaged reducing the pump efficiency and often resulting
in failure.

An operation and maintenance schedule should identify a frequency of
inspection to identify the need for debris and sediment removal.

### Provision for Replacing Pumps

Pumping stations should be designed for easy maintenance and/or removal
and replacement of pumps. The alternatives usually are a permanent hoist
in the station or use of mobile hoisting equipment.

### Typical Problems

The following is a list of design practices that can result in
unnecessary maintenance requirements:

-   poor siting of the station making access difficult,

-   inadequate erosion control and slope stability measures producing
    excessive sediment and resulting in excessive wear of pump
    equipment,

-   inadequate wet well dimensions causing vortexing or cavitation
    leading to excessive noise and wear,

-   improper orientation of pumps causing vortexing, noise and wear, and

-   poor trash handling resulting in clogging.

Generally, if the considerations and criteria discussed in this manual
are followed, the potential for significant maintenance problems will be
minimized.

### Troubleshooting

Table 12‑1 identifies some specific problems, their likely cause(s), and
possible mitigation measures.

87. []{#__RefHeading___Toc509049868 .anchor}Table 12‑20. Pump operation
    problems and typical solutions

+-----------------------+-----------------------+-----------------------+
| **Condition**         | **Likely Cause**      | **M                   |
|                       |                       | itigation/Avoidance** |
+-----------------------+-----------------------+-----------------------+
| Frequent flooding of  | On and off sensor     | -   Adjust sensors to |
| road low point        | levels incorrectly    |     activate at       |
|                       | set                   |     design levels     |
|                       |                       |                       |
|                       |                       | -   Check sensors     |
|                       |                       |     during pump       |
|                       |                       |     testing           |
+-----------------------+-----------------------+-----------------------+
|                       | Clogged intake        | -   Provide trash     |
|                       |                       |     rack and frequent |
|                       |                       |     cleaning          |
+-----------------------+-----------------------+-----------------------+
|                       | Inadequate pump       | -   Add pump(s),      |
|                       | capacity              |                       |
|                       |                       | -   replace pumps, or |
|                       |                       |                       |
|                       |                       | ```{=html}            |
|                       |                       | <!-- -->              |
|                       |                       | ```                   |
|                       |                       | -   add storage unit  |
+-----------------------+-----------------------+-----------------------+
| Rapid cycling         | On and off sensor     | -   Adjust sensors to |
|                       | levels incorrectly    |     activate at       |
|                       | set                   |     design levels     |
|                       |                       |                       |
|                       |                       | ```{=html}            |
|                       |                       | <!-- -->              |
|                       |                       | ```                   |
|                       |                       | -   Check sensors     |
|                       |                       |     during pump       |
|                       |                       |     testing           |
+-----------------------+-----------------------+-----------------------+
|                       | Inadequate usable     | -   Increase storage  |
|                       | storage               |     unit capacity     |
+-----------------------+-----------------------+-----------------------+
|                       | Excessive pump size   | -   Increase storage  |
|                       |                       |     unit capacity, or |
|                       |                       |                       |
|                       |                       | ```{=html}            |
|                       |                       | <!-- -->              |
|                       |                       | ```                   |
|                       |                       | -   Add low flow pump |
+-----------------------+-----------------------+-----------------------+
| Excessive             | Cavitation or         | -   Increase          |
| noise/vibration       | vortexing             |     submergence and   |
|                       |                       |     pump clearances,  |
|                       |                       |     or                |
|                       |                       |                       |
|                       |                       | -   add               |
|                       |                       |     baffles/vortex    |
|                       |                       |     suppressors       |
+-----------------------+-----------------------+-----------------------+
|                       | Incorrectly aligned   | -   Check             |
|                       | pump                  |     installation and  |
|                       |                       |     adjust alignment  |
+-----------------------+-----------------------+-----------------------+
| Excessive wear on     | Rapid cycling,        | See rapid cycling and |
| pumps                 | cavitation or         | excessive             |
|                       | vortexing             | noise/vibration       |
+-----------------------+-----------------------+-----------------------+
| Overheating of pumps  | Rapid Cycling         | See rapid cycling     |
+-----------------------+-----------------------+-----------------------+
| Sump pump failure     | Low fluidity of sump  | Provide flushing      |
|                       | sediment.             | system                |
+-----------------------+-----------------------+-----------------------+

### Inspection and Maintenance Schedule

The highway agency should develop a maintenance log that includes:

-   the required frequency of inspection,

-   an inspection check list, and

-   routine maintenance measures.

### Monitoring

By necessity, highway stormwater pumps must operate automatically. There
are numerous components that may be subject to failure. With only one or
two pump stations, it may be efficient enough to rely on local highway
maintenance offices to manually monitor the condition of the stations.
As the number of stations in an agency's inventory increase, it becomes
feasible and desirable to use some kind of automated monitoring system.
Typical features to monitor include:

-   high water in the wet well,

-   number of starts for each motor,

-   cumulative operation time of each pump,

-   leakage in dry well (for dry-pit stations),

-   debris levels/amounts,

-   sediment levels,

-   motor/engine failure,

-   ambient temperature,

-   temperature of bearings and motor wiring,

-   smoke,

-   gases, and

-   unauthorized entry.

The simplest type of automated warning system is a flashing light or
siren that relies on locals to call in to a listed number. Preferred
systems allow remote telemetering of any of the above alarms, or data,
to a monitoring station.

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# RETROFITTING EXISTING SYSTEMS

## Introduction

Existing pump stations may become inadequate, undependable or
troublesome, often requiring excessive maintenance. Some kind of
retrofit may be necessary. The type of retrofit will depend on the cause
of the deficiency or the extent of change. This chapter identifies
various problems that relate to hydraulic deficiencies and methods to
mitigate them.

## Identification of Deficiency

Usually, retrofit of an existing station is needed because of proposed
changes to the highway or as a result of continual or increasingly poor
performance of a system. Maintenance records should provide some insight
into the type and possible cause of the problem. In some cases, the
cause may be reasonably easy to identify and relatively cheap to
mitigate. However, oftentimes the cause is difficult to ascertain and
solutions are likely to be expensive. Some circumstances may warrant
developing small-scale models to hone in on the specific problem and
test alternative solutions.

## Highway Modifications

If the highway is to be modified, the runoff rates and collection system
may change. In some cases, the combination of age of the existing system
and increase in load to the pump station may warrant a complete redesign
of the system. However, the designer should evaluate the system to
determine if non structural or less extensive structural measures than
replacement are viable.

### Increased Pumping Capacity

The most likely need associated with a significant modification to the
highway is the need to handle a higher inflow rate and total volume.
Consideration should be given to using submersible pumps. Typically,
they require lower cycle times for the same capacity, thus the required
usable storage is lower than many other pump types. This could help
reduce the need to adjust the wet well structure or collection system
size. Recent developments may make submersible pumps a viable
alternative for consideration now. When the pump station was originally
developed, adequate submersible pumps were generally not available.

Any need to increase the pump capacity will warrant an evaluation of the
station performance using the design procedures detailed in Chapters 7,
8, and 9.

### Increased Storage Capacity

It may be cost effective to provide additional available and usable
storage and avoid the need to replace the pumping equipment and
controls. The addition of a storage unit or supplemental collection line
conduit need not require the removal or reinstallation of any pump
equipment. However, it is likely that the sensor levels for the pump
switching will require adjustment to optimize the use of the new
storage. It will be necessary to perform mass curve routing and cycling
checks, as discussed in Chapters 7 and 8, to check the station
performance with the new storage.

### Elimination of the Structure

The designer should consider the possibility of constructing a gravity
drain. The economics of this alternative may have changed since the
original construction.

## Poor Station Location Or Discharge Conditions

The following table identifies some problems and potential solutions
that may relate to poor station location or discharge conditions.

88. []{#__RefHeading___Toc509049869 .anchor}Table 13‑21. Site problems
    and possible mitigation

+-----------------------------------+----------------------------------+
| **Problem**                       | **Possible Mitigation**          |
+-----------------------------------+----------------------------------+
| Silting due to poor erosion       | 1.  Stabilize exposed areas      |
| control                           |                                  |
|                                   | 2.  Add sediment basin           |
|                                   |                                  |
|                                   | 3.  Add storage unit with        |
|                                   |     sediment trap and sludge     |
|                                   |     pump                         |
|                                   |                                  |
|                                   | 4.  Add sediment flushing system |
+-----------------------------------+----------------------------------+
| Silting due to slope failures     | 1.  Reduce slopes                |
|                                   |                                  |
|                                   | 2.  Protect slopes               |
|                                   |                                  |
|                                   | 3.  Use retaining wall           |
+-----------------------------------+----------------------------------+
| Pump house flooded by high        | Move station to higher ground    |
| magnitude floods, but pumps       |                                  |
| operating properly                |                                  |
+-----------------------------------+----------------------------------+
| Outfall backwater submerges       | 1.  Improve outfall conditions   |
| discharge line                    |     to reduce backwater          |
|                                   |                                  |
|                                   | 2.  Increase elevation of        |
|                                   |     discharge line and check     |
|                                   |     pump operation or replace    |
|                                   |     pumps                        |
+-----------------------------------+----------------------------------+

## Hydraulic-Related Deficiencies of Pump Stations

The following table identifies typical hydraulic deficiencies of pump
stations and possible causes.

89. []{#__RefHeading___Toc509049870 .anchor}Table 13‑22. Possible causes
    of pump station deficiencies

+--------------------------+-------------------------------------------+
| **Deficiency**           | **Possible Cause(s)**                     |
+--------------------------+-------------------------------------------+
| Excessive pump cycling   | Oversized pumps, insufficient storage,    |
|                          | incorrect switching levels or sequence.   |
+--------------------------+-------------------------------------------+
| Excessive pumping noise  | Cavitation or vortexing due to low        |
|                          | submergence, poor flow alignment, high    |
|                          | velocities in the wet well or low NPSH.   |
+--------------------------+-------------------------------------------+
| Excessive and frequent   | 1.  Clogging of pump intake               |
| flooding                 |                                           |
|                          | 2.  Poor outfall conditions               |
|                          |                                           |
|                          | 3.  Insufficient pump capacity            |
|                          |                                           |
|                          | 4.  Insufficient storage capacity         |
|                          |                                           |
|                          | 5.  Worn impellers                        |
+--------------------------+-------------------------------------------+
| Excessive pump wear      | Cavitation, vortexing, poor maintenance,  |
|                          | high sediment load                        |
+--------------------------+-------------------------------------------+
| Excessive energy         | Cavitation, vortexing, poor pump          |
| (electricity/fuel)       | selection, leaks, damaged impeller        |
| requirements             |                                           |
+--------------------------+-------------------------------------------+
| Frequent clogging of     | Excessive debris or sediment due to poor  |
| pumps                    | screening or poor flushing                |
+--------------------------+-------------------------------------------+

Many of the above problems relate to the same cause. Other deficiencies
may exist, such as non-compliance with current OSHA safety and NEMA
standards, but are considered beyond the scope of this manual.

## Replacement Of Pumps

The following are typical reasons for replacing the pump units of a
station:

-   pump and driver have exceeded useful life,

-   sump dimensions appear to be satisfactory, but pumps cannot handle
    desired capacity, and

-   life cycle cost of new pumps is lower than operating cost of
    existing pumps.

In many cases it will be necessary to replace the pumps because of
excessive wear. Any time that pump replacement is considered, the entire
design procedures, detailed in Chapters 7, 8, and 9, should be addressed
to ensure efficient design and determine what, if any, adjustments to
the sump dimensions and switching may be necessary.

Figure 13‑1 shows one of three existing electrical motor-drives for
vertical shaft pumps in a confined station on US 59 in Houston. The
pumps were more than 25 years old. The electrical control system was
replaced and new submersible pumps installed. The lower cycling
requirements of the submersible pumps compared with the existing pumps
avoided the need to adjust the wet well structure.

![](media/image82.png){width="3.4159722222222224in"
height="4.886805555555555in"}

[]{#__RefHeading___Toc509049992 .anchor}Figure 13‑76. Old motor drive
for vertical pump to be replaced

## Leakage

Leakage can cause a significant reduction in efficiency and an increase
in power requirements. Typical causes of leakage are worn bearings and
seals, and faulty valves. Wear and tear might be attributed to the age
of the system. However, there may be other causes such as:

-   excessive vibration, friction and impact caused by cavitation or
    vortexing,

-   hydraulic transients such as water hammer resulting from sudden pump
    operation or termination,

-   inadequate or absent pressure release valves, and

-   excessive sediment, debris loads, or corrosion.

Normal maintenance should ensure that the integrity of seals and
bearings is maintained. Possible remedies for vortexing, cavitation, and
excessive sediment or debris are discussed below. If water hammer is the
likely cause, provision for slow-closing valves may reduce future
problems by reducing the rate of pressure changes. The pump manufacturer
should be consulted for recommendations on appropriate valve types and
locations for the specific pumps used.

## Modifications to Pump Switching

Rapid cycling will likely cause overheating and excessive wear of
electric motors. Adjustments to the switching elevations and sequence
may resolve the problem if the following are true:

-   the pumps are not beyond repair or similar replacement pumps are
    intended,

-   no serious flooding of the pump station has been experienced,

-   there is significant total storage available, and

-   the pumps are determined to be cycling to quickly.

Two specific mitigation measures are:

1.  Increase the elevation at which the pumps switch on. This will
    require an evaluation of the station performance using the mass
    curve routing procedure discussed in Chapter 7.

```{=html}
<!-- -->
```
19. Use an alternating switching scheme, which is the preferred design
    measure.

##  Modifications to Wet Well

Problems such as vortexing and cavitation may not require replacement of
the pump unit unless there is excessive wear. Oftentimes, such problems
are a result of incorrect sump dimensions and clearances. In order to
determine if modifications to the sump dimensions and clearances will
reduce the problems, it is necessary to compare recommended criteria
with actual dimensions to identify any significantly deficient values.
If any actual values are deficient, some adjustment will be appropriate.
Depending on the extent of the deficiency, adjustments to the existing
sump that avoid replacing or significantly modifying the wet well
structure may suffice.

###  Vortexing

The following table provides some different mitigation measures for
deficiencies in sump dimensions and clearances. The table also
references appropriate figures. Generally, these measures may be
combined.

90. []{#__RefHeading___Toc509049871 .anchor}Table 13‑23. Mitigation
    measures for deficiencies related to vortexing

+--------------------------+--------------------------+---------------+
| Condition                | Mitigation Measure       | Reference     |
|                          |                          | Figure        |
+--------------------------+--------------------------+---------------+
| Inflow to pump distance  | Disperse flow using      | Figure 13‑2   |
| too short                | baffles or vanes         |               |
+--------------------------+--------------------------+---------------+
| Pumps aligned with       | Realign pumps            | Figure 13‑3   |
| inflow                   | perpendicular to inflow  |               |
+--------------------------+--------------------------+---------------+
| Submerged vortices       | Place cone under intake  | Figure 13‑4   |
| resulting from low       |                          |               |
| submergence              |                          |               |
+--------------------------+--------------------------+---------------+
| Excessive vortexing due  | Add suction umbrella or  | Figure 13‑5   |
| to low submergence depth | bell extension and       |               |
|                          | splitter                 |               |
+--------------------------+--------------------------+---------------+
| Backwall distance too    | 1.  Triangular backwall  | Figure 13‑6   |
| large and submerged      |     and base splitter    |               |
| vortices present         |                          |               |
|                          | 2.  False backwall       |               |
+--------------------------+--------------------------+---------------+
| Eddying in sump          | Smooth all transitions   | Figure 13‑7   |
|                          | and sharp protruding     |               |
|                          | edges using grout or     |               |
|                          | other materials          |               |
+--------------------------+--------------------------+---------------+
| Sump velocities exceed 1 | Place turning vanes on   |               |
| m/s (3 fps)              | pump bowl                |               |
+--------------------------+--------------------------+---------------+

![](media/image83.png){width="4.0in" height="2.4993055555555554in"}

[]{#__RefHeading___Toc509049993 .anchor}Figure 13‑77. Addition of
baffles in sump

![](media/image84.png){width="3.848611111111111in"
height="1.8743055555555554in"}

[]{#__RefHeading___Toc509049994 .anchor}Figure 13‑78. Pump realignment

![](media/image85.png){width="3.1659722222222224in"
height="2.7215277777777778in"}

[]{#__RefHeading___Toc509049995 .anchor}Figure 13‑79. Addition of cone
under intake

![](media/image86.png){width="4.999305555555556in" height="3.0in"}

[]{#__RefHeading___Toc509049996 .anchor}Figure 13‑80. Addition of bell
extension and splitter

![](media/image87.png){width="4.999305555555556in"
height="2.6798611111111112in"}

[]{#__RefHeading___Toc509049997 .anchor}Figure 13‑81. Addition of
backwall splitter

![](media/image88.png){width="4.0in" height="1.5006944444444446in"}

91. []{#__RefHeading___Toc509049998 .anchor}Figure 13‑82. Addition of
    grouted transition

###  Cavitation

A primary cause of cavitation is insufficient net positive suction head
available (NPSHA). The Hydraulic Institute suggests that minimum
submergence values are based on minimizing the potential for vortexing.
The net positive suction head required (NPSHR) is specific to a
manufacturer's pump and the hydraulic conditions. If the NPSHA is lower
than NPSHR, cavitation is likely. In fact, it is still likely under some
conditions if NPSHA is greater than NPSHR. Therefore, a safety factor or
margin is suggested. Non-structural mitigation options include
increasing first pump-on elevation or changing pump to one with a lower
NPSHR.

If the pump switching elevations are altered, it will be necessary to
evaluate the station performance using the mass routing procedure
described in Section 7.3.1 - Procedure to Perform Mass Curve Routing.
This is also the case if the pumps are replaced with pumps of a
different capacity to the original design.

###  Rapid Cycling

Rapid cycling may result from one or more of the following:

-   small sump and collection system storage,

-   first pump start elevation set too low, or

-   pump capacity too large.

By inference, non-structural remedies may include increasing the first
pump start elevation to achieve a usable storage that results in an
adequate minimum cycle time, or adding a low flow pump.

###  Excessive Sediment, Debris and Corrosion

Excessive sediment or debris can clog the pump intake and erode or chip
and fracture the impeller vanes. Additionally, corrosion can contribute
to the degradation of the vanes, bearings and seals. Corrosion can be
significant if the pump is continually immersed in sump water and is
exacerbated by hazardous spills.

If minimal provision for screening of trash has been made, the obvious
remedy is to improve the trash removal capability. The following are
some specific suggestions:

-   Use screened curb opening inlets or bicycle-safe grate inlets. Refer
    to the FHWA publication, *Urban Storm Drain Design*^10^ for detailed
    discussion of inlet design.

-   If existing trash rack allows clearance below first switch-on
    elevation, or between the top of the rack and the maximum water
    level in the wet well, replace the trash rack.

-   If no specific schedule and guidance for inspection and maintenance
    exists, develop a plan and schedule and ensure that it is observed.

-   If practicable, add automatic trash removal system.

-   Minimize potential for trash buildup using street sweeping and trash
    collection.

If sediment build up is a problem, several possible remedial solutions
exist. The preferred approach is to modify the sump to minimize
horizontal floor area in the wet well, provide storage unit floor slopes
of 2 % and allow the main pump to discharge sediment-laden water.
Chapter 9, SUMP DIMENSIONS AND SYSTEM CHECKS provides discussion on
design measures to accommodate sediment-laden water in rectangular and
circular wells. The following are other alternatives:

-   Add a self-flushing system and sludge/sump pump.

-   Manually flush the sump and pump it dry with portable equipment
    after each significant storm or after a specified period, whichever
    is more frequent.

-   Replace pumps with non-clog type pumps of similar performance
    characteristics.

-   Provide a forebay to a lower sump where sediment can settle without
    interfering with the main pumps and add a sump pump.

-   Provide a sediment trap upstream of the pump station.

Any of the above remediation measures that evacuate the sump will also
help reduce the potential for corrosion of the impeller and bearings.

###  Replacing Wet Well

The remedies discussed in Vortexing (Section 13.9.1), Cavitation
(Section 13.9.2), and Rapid Cycling (Section 13.9.3) are aimed at
avoiding structural modifications. If actual sump dimensions are
inconsistent with the recommended criteria, structural modifications may
be necessary unless a pump replacement alternative is practicable. If
substantial changes are made, it will be necessary to perform all the
design procedures indicated in Chapters 6, 7, 8, and 9.

## Comparison Of Alternate Methods

The cost of retrofitting a pump station may far exceed the original cost
of construction. Therefore, the decision of what remediation measures to
undertake should be based on:

-   an economic evaluation of the viable alternatives, including a
    gravity drain,

-   an appraisal of the added benefits that each alternative is likely
    to provide, and

-   local design, construction, operation and maintenance experience.

# REFERENCES

1.  Stewart, Harry L., *Pumps*, revised by T. Philbin, Bobbs-Merill Co.,
    Inc., 1984.

2.  Manual for Highway Storm Water Pumping Stations Vol. 1, U. S.
    Department of Transportation, Federal Highway Administration, Report
    No. FHWA-IP-82-17-Vol.1, October 1982.

3.  Dicmas, John L., *Vertical Turbine, Mixed Flow, and Propeller
    Pumps*, Mcgraw-Hill Inc. Book Company, 1987.

4.  Volk, Michael W., *Pump Characteristics and Applications,* Volk &
    Associates, Inc. Oakland, California, Marcel Dekker Publishers,
    1996.

5.  McCuen, Richard H., Johnson, Peggy A. & Ragan, Robert M., *Highway
    Hydrology, Hydraulic Design Series No. 2,* Federal Highway
    Administration, Washington, D. C., U. S. Department of
    Transportation, Publication No. FHWA-SA-96-067, September 1996.

6.  *Federal Aid Policy Guide*, Federal Highway Administration,
    Washington D.C.

7.  *A Policy on Geometric Design of Highways and Streets*, American
    Association of State Highway and Transportation Officials (AASHTO),
    Suite 225, 444 North Capitol Street, N.W. Washington, D.C. 20001

8.  *Technical Release 55, Urban Hydrology for Small Watersheds* (TR55),
    Natural Resource Conservation Service, 1981

9.  *Technical Release 20, Hydrology* (TR 20), Natural Resource
    Conservation Service

10. Brown, S. A., Stein, S. M. & Warner, J. C., *Urban Drainage Design
    Manual, Hydraulic Engineering Circular No. 22*, U. S. Department of
    Transportation, Federal Highway Administration, Report No.
    FHWA-SA-96-078, November 1996.

11. Schall, James, D., & Richardson, Everitt, V., *Introduction to
    Highway Hydraulics, Hydraulic Design Series No. 4,* Federal Highway
    Administration, Washington, D. C., U. S. Department of
    Transportation, Publication No. FHWA HI 97-028, June 1997.

12. *Centrifugal Pump Design and Application,* Hydraulic Institute,

13. *Design of Rip Rap Revetment*, Hydraulic Engineering Circular, No.
    11, 1989*,* Federal Highway Administration, Washington, D. C., U. S.
    Department of Transportation.

14. *National Manual for Uniform Traffic Control Devices*

15. American National Standard for Pump Intake Design, ANSI/HI 9.8-1998,
    Hydraulic Institute, New Jersey, December, 1998.

16. HY-22, Federal Highway Administration

17. Germain, James E., et al., *Design of Wastewater and Stormwater
    Pumping Stations*, Manual of Practice No. FD-4, prepared by Task
    Force on Pumping Stations under the direction of the Facilities
    Development Subcommittee Technical Practice Committee, Walter
    Pollution Control Federation, Washington D. C. 20037, 1981.

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A.  []{#__RefHeading___Toc481572158 .anchor}GLOSSARY

The following terms appear throughout this document and are defined as
they relate to highway stormwater pump stations.

+--------------------+-------------------------------------------------+
| **Term**           | **Definition**                                  |
+====================+=================================================+
| Access hole        | A hole through which one can access an          |
|                    | underground element for repairs or inspections. |
+--------------------+-------------------------------------------------+
| Affinity Laws      | Rules that govern the performance of a          |
|                    | centrifugal pump when speed or impeller         |
|                    | diameter is changed.                            |
+--------------------+-------------------------------------------------+
| Air Valve          | A valve by which the entrance or escape of air  |
|                    | can be regulated.                               |
+--------------------+-------------------------------------------------+
| Available Storage  | Total volume in storage system that is below    |
|                    | the allowable highwater and above the lowest    |
|                    | pumping level.                                  |
+--------------------+-------------------------------------------------+
| Backwall           | The vertical surface behind a pump's intake     |
|                    | bell.                                           |
+--------------------+-------------------------------------------------+
| Baffles            | Obstructions to the flow that are aligned to    |
|                    | distribute flow evenly between pumps.           |
+--------------------+-------------------------------------------------+
| Bay                | A portion of the sump containing one pump.      |
+--------------------+-------------------------------------------------+
| Bearings           | Motor bearings, which are either plain or       |
|                    | anti-friction, support and control the motion   |
|                    | of a rotating shaft.                            |
+--------------------+-------------------------------------------------+
| Bell               | The flared entrance to a pump or its suction    |
|                    | pipe.                                           |
+--------------------+-------------------------------------------------+
| Best Efficiency    | The discharge rate and total head at which the  |
| Point              | ratio of water power to brake power (hydraulic  |
|                    | efficiency) is the highest it can be for the    |
|                    | specific pump.                                  |
+--------------------+-------------------------------------------------+
| Brake Power        | Brake power, BP (brake horsepower, BHP, in      |
|                    | English units) is the actual amount of power    |
|                    | required to be supplied to the pump to maintain |
|                    | the water power.                                |
+--------------------+-------------------------------------------------+
| Caisson            | A watertight, usually circular precast          |
|                    | enclosure.                                      |
+--------------------+-------------------------------------------------+
| Cavitation         | Hydraulic phenomenon in which vapor bubbles     |
|                    | form and suddenly collapse (implode) as they    |
|                    | move through a pump impeller. The formation of  |
|                    | cavities between the back surface of an         |
|                    | impeller blade and the liquid normally in       |
|                    | contact with it.                                |
+--------------------+-------------------------------------------------+
| Centrifugal Pump   | A pump in which liquid is forced into the inlet |
|                    | side of the pump casing by atmospheric pressure |
|                    | or some upstream pressure. As the impeller      |
|                    | rotates, liquid moves toward the discharge side |
|                    | of the pump, which creates a void or reduced    |
|                    | pressure area at the impeller inlet. The        |
|                    | pressure at the pump casing inlet, which is     |
|                    | higher than this reduced pressure at the        |
|                    | impeller inlet, forces additional liquid into   |
|                    | the impeller to fill the void.                  |
+--------------------+-------------------------------------------------+
| Check Valve        | A pipe fitting used to prevent backflow to the  |
|                    | pumps and subsequent recirculation.             |
+--------------------+-------------------------------------------------+
| Close-coupled pump | Pump in which the motor and pump impeller share |
|                    | the same shaft. Also, the pump bearings and     |
|                    | motor bearings are the same.                    |
+--------------------+-------------------------------------------------+
| Closed impeller    | The closed impeller has a shroud covering the   |
|                    | vanes on the suction or front side and an       |
|                    | axially oriented hub that provides the inlet    |
|                    | for the liquid into the vane passageways.       |
+--------------------+-------------------------------------------------+
| Collection System  | The system of conveyance elements that collect  |
|                    | the stormwater and direct it to the pump        |
|                    | station. The system usually includes channels,  |
|                    | ditches, inlet lines and storm drain conduits.  |
+--------------------+-------------------------------------------------+
| Coupling           | A fixture used to join two pipes. A typical     |
|                    | coupling uses two flanged rings separated by a  |
|                    | sleeve with rubber gaskets.                     |
+--------------------+-------------------------------------------------+
| Start Elevation    | Elevation at which a pump is set to begin       |
|                    | operating.                                      |
+--------------------+-------------------------------------------------+
| Stop Elevation     | Elevation at which a pump is set to cease       |
|                    | operating.                                      |
+--------------------+-------------------------------------------------+
| Cycling            | The starting, stopping then starting of a pump. |
+--------------------+-------------------------------------------------+
| Design Capacity    | The total stormwater runoff rate for which the  |
|                    | pump station is designed. Also may refer to     |
|                    | rate at which an individual pump will operate   |
|                    | at the design point.                            |
+--------------------+-------------------------------------------------+
| Design Point       | The point of intersection of the system curve   |
|                    | and the selected pump performance curve.        |
+--------------------+-------------------------------------------------+
| Diffuser           | A piece of casing, adjacent to the impeller     |
| (multi-volute)     | exit, which has multiple passages of increasing |
|                    | area for converting velocity to pressure        |
+--------------------+-------------------------------------------------+
| Discharge          | The rate of flow ejected from the pump          |
+--------------------+-------------------------------------------------+
| Discharge Line     | A conduit through which the storm water exits   |
|                    | the pump station.                               |
+--------------------+-------------------------------------------------+
| Double suction     | The action of a double suction impeller where   |
|                    | the liquid enters the impeller from both sides. |
+--------------------+-------------------------------------------------+
| Double volute      | A hybrid between a single volute casing and a   |
|                    | diffuser casing. Typically used in larger       |
|                    | centrifugal pumps to reduce radial loads.       |
+--------------------+-------------------------------------------------+
| Dry well           | The dry well of a dry-pit station contains the  |
|                    | pumps and pumping accessories that discharge    |
|                    | the storm water from the wet-well.              |
+--------------------+-------------------------------------------------+
| Dry-Pit Station    | A pump station consisting of two chambers: a    |
|                    | dry well and a wet-well. The water accumulates  |
|                    | in the wet well and is pumped out by pumps      |
|                    | installed in the dry well.                      |
+--------------------+-------------------------------------------------+
| Elbow              | A curved water passage by which water either    |
|                    | leaves the pump (discharge elbow) or enters the |
|                    | pump (suction elbow).                           |
+--------------------+-------------------------------------------------+
| Flap Gate          | A circular device attached to the end of the    |
|                    | discharge line to prevent backflow from the     |
|                    | outfall to the discharge line.                  |
+--------------------+-------------------------------------------------+
| Flap Valve         | A check valve that uses a rubber flap           |
+--------------------+-------------------------------------------------+
| Flow line          | The invert of a conduit                         |
+--------------------+-------------------------------------------------+
| Force Main         | A pressurized discharge line.                   |
+--------------------+-------------------------------------------------+
| Forebay            | An area in the wet well between the storage     |
|                    | unit and the individual pump bays.              |
+--------------------+-------------------------------------------------+
| Friction Loss      | The energy loss in overcoming friction. Usually |
|                    | determined as an equivalent depth of water      |
|                    | (head).                                         |
+--------------------+-------------------------------------------------+
| Gasket             | Resilient material of proper shape and          |
|                    | characteristics for use in joints between parts |
|                    | to prevent leakage.                             |
+--------------------+-------------------------------------------------+
| Gate Valve         | Devices used on collection lines to shut-off or |
|                    | permit water flow. The gate valve is not        |
|                    | intended to regulate flow.                      |
+--------------------+-------------------------------------------------+
| Grate Inlet        | A lattice covering that permits flow to enter   |
|                    | the storm drain conduit or storage unit.        |
+--------------------+-------------------------------------------------+
| Head               | The measure of pressure expressed in equivalent |
|                    | height of water.                                |
+--------------------+-------------------------------------------------+
| Hydraulic Grade    | A line corresponding to the water level within  |
| Line               | a channel or a line that represents the         |
|                    | pressure level in an enclosed conduit that is   |
|                    | flowing full.                                   |
+--------------------+-------------------------------------------------+
| Hydraulic          | An entity consisting primarily of pump          |
| Institute          | manufacturer's that establishes and publishes   |
|                    | standards for the design and use of pumps.      |
+--------------------+-------------------------------------------------+
| Hydrograph         | A representation of stormwater runoff versus    |
|                    | time.                                           |
+--------------------+-------------------------------------------------+
| Impeller           | The bladed member of the rotating assembly of   |
|                    | the pump which imparts the principal force for  |
|                    | the liquid pumped                               |
+--------------------+-------------------------------------------------+
| Increaser          | A transition from a smaller pipe diameter to    |
|                    | larger pipe diameter                            |
+--------------------+-------------------------------------------------+
| Inflow             | A flowing in or into.                           |
+--------------------+-------------------------------------------------+
| Inflow Mass Curve  | A representation of cumulative inflow volume    |
|                    | versus time.                                    |
+--------------------+-------------------------------------------------+
| Intake             | The place at which a fluid is taken into a      |
|                    | pipe, channel, etc.                             |
+--------------------+-------------------------------------------------+
| Invert             | The inside bottom elevation of a conduit or     |
|                    | well at a specified location.                   |
+--------------------+-------------------------------------------------+
| Manifold           | A pipe terminal having several intake openings  |
|                    | and a common discharge end.                     |
+--------------------+-------------------------------------------------+
| Mass Curve Routing | The process of computing the volume of outflow  |
|                    | as a function of the inflow volume, pumping     |
|                    | rates, and storage.                             |
+--------------------+-------------------------------------------------+
| Mass Inflow Curve  | A curve representing the cumulative inflow      |
|                    | volume with respect to time.                    |
+--------------------+-------------------------------------------------+
| Mechanical Seal    | A device used to help prevent leakage and       |
|                    | reduce vibration, rotating friction and         |
|                    | corrosion of the pump shaft.                    |
+--------------------+-------------------------------------------------+
| Mixed Flow         | A combination of radial and axial flow through  |
|                    | an impeller                                     |
+--------------------+-------------------------------------------------+
| Net Positive       | Net positive suction head required (NPSHR) is   |
| Suction Head       | the head above vapor pressure head required to  |
| Required           | ensure that cavitation does not occur at the    |
|                    | impeller.                                       |
+--------------------+-------------------------------------------------+
| Open impeller      | The vanes of an open impeller are exposed on    |
|                    | the suction or front side.                      |
+--------------------+-------------------------------------------------+
| Operating Range    | The range of total dynamic head over which the  |
|                    | pumps in a system will operate.                 |
+--------------------+-------------------------------------------------+
| OSHA               | The Occupational Safety and Health              |
|                    | Administration is an agency which establishes   |
|                    | the safety requirements for pump stations.      |
+--------------------+-------------------------------------------------+
| Outflow            | The storm water discharged by the pumps.        |
+--------------------+-------------------------------------------------+
| Packing            | Material used to prevent leakage -- usually a   |
|                    | woven fiber and lubricant                       |
+--------------------+-------------------------------------------------+
| Power Factor       | The ratio of actual power to the apparent power |
|                    | consumed by an electric circuit.                |
+--------------------+-------------------------------------------------+
| Propeller          | A propeller is a device consisting of a central |
|                    | hub with radiating blades used in low head,     |
|                    | axial-flow, vertical pumps.                     |
+--------------------+-------------------------------------------------+
| Pump               | A device that increases the static pressure of  |
|                    | a fluid. A pump adds energy to a body of fluid  |
|                    | in order to move it from one point to another.  |
+--------------------+-------------------------------------------------+
| Pump Bowl          | A vessel within which the impeller rotates and  |
|                    | imparts energy to the water that is raised up   |
|                    | the pump column.                                |
+--------------------+-------------------------------------------------+
| Pump Column        | The vessel above the pump impeller that conveys |
|                    | the discharge of a vertical pump to the         |
|                    | discharge line.                                 |
+--------------------+-------------------------------------------------+
| Pump Cycling Time  | Cycling refers to the time between starts of a  |
|                    | given a pump. The shorter the cycling time, the |
|                    | more frequent a pump must start and stop.       |
+--------------------+-------------------------------------------------+
| Pump Discharge     | A representation of stage versus discharge for  |
| Curve              | a system of pumps.                              |
+--------------------+-------------------------------------------------+
| Pump House         | An enclosed structure used to protect the pump  |
|                    | control equipment, pump drivers and ancillary   |
|                    | equipment.                                      |
+--------------------+-------------------------------------------------+
| Pump Performance   | A representation of the changing discharge rate |
| Curve              | with total dynamic head for a given pump.       |
+--------------------+-------------------------------------------------+
| Pump Sequencing    | The order in which pumps are activated and      |
|                    | deactivated                                     |
+--------------------+-------------------------------------------------+
| Pump Station       | The collection of components used to lift       |
|                    | highway stormwater runoff. A station includes   |
|                    | the storage unit, wells, pumps, pump house and  |
|                    | ancillary equipment.                            |
+--------------------+-------------------------------------------------+
| Reducer            | An element that is use to transition from one   |
|                    | size pipe to a smaller one.                     |
+--------------------+-------------------------------------------------+
| Retrofit           | The replacement of various pump station         |
|                    | components, typically the pumps.                |
+--------------------+-------------------------------------------------+
| Shaft              | The cylindrical unit used to drive the pump     |
+--------------------+-------------------------------------------------+
| Single stage       | A pump with only one impeller.                  |
+--------------------+-------------------------------------------------+
| Single volute      | A spiral-like casing which directs the flow     |
|                    | from the impeller at the center of the casing   |
|                    | to the periphery. The shape of the volute       |
|                    | converts a decrease in flow velocity at the     |
|                    | periphery into a pressure increase.             |
+--------------------+-------------------------------------------------+
| Soffit             | The inside top of a conduit.                    |
+--------------------+-------------------------------------------------+
| Specific Speed     | Specific speed is a dimensionless number        |
|                    | expressed in terms of head per stage, pump      |
|                    | capacity and shaft speed. Specific speed not    |
|                    | only places an upper limit on the shaft speed   |
|                    | for any particular combination of total head,   |
|                    | flow, and suction conditions, but it also       |
|                    | determines the form and proportions of the      |
|                    | impeller.                                       |
+--------------------+-------------------------------------------------+
| Stage-Storage      | A curve that represents the storage that is     |
| Curve              | available within the system at various stages.  |
+--------------------+-------------------------------------------------+
| Static Head        | The change in elevation which the water must    |
|                    | undergo. For typical stormwater pump stations,  |
|                    | static head is normally measured between the    |
|                    | water level in the sump and the higher of the   |
|                    | water level at the end of the discharge side of |
|                    | the pump and the center of the end of the       |
|                    | discharge pipe.                                 |
+--------------------+-------------------------------------------------+
| Storage            | The provision for holding a volume of           |
|                    | stormwater for the following purposes:          |
|                    |                                                 |
|                    | -   reducing the size and number of required    |
|                    |     pumps, and                                  |
|                    |                                                 |
|                    | ```{=html}                                      |
|                    | <!-- -->                                        |
|                    | ```                                             |
|                    | -   ensuring minimum cycling times.             |
+--------------------+-------------------------------------------------+
| Storage Unit       | A storage unit is a chamber that is provided to |
|                    | achieve a desired storage volume in excess of   |
|                    | the storage provided by the collection system.  |
+--------------------+-------------------------------------------------+
| Stormwater         | Rainfall runoff from the highway system and     |
|                    | associated drainage area.                       |
+--------------------+-------------------------------------------------+
| Stuffing Box       | A packed casing through which the pump shaft    |
|                    | extends that contains either a gland or         |
|                    | mechanical seal to prevent leakage.             |
+--------------------+-------------------------------------------------+
| Submergence        | Submergence is the static head of water         |
|                    | required above the intake of the pump to        |
|                    | prevent vortexing and cavitation.               |
+--------------------+-------------------------------------------------+
| Submersible Pump   | A close-coupled pump and motor that are         |
|                    | designed to be immersed. The motor is often     |
|                    | encapsulated and filled with oil which is       |
|                    | separated from the pumped liquid by a           |
|                    | mechanical seal.                                |
+--------------------+-------------------------------------------------+
| Suction Bell       | Suction bell velocity is defined as flow        |
| Velocity           | divided by area measured at the outside         |
|                    | diameter of the pump bell.                      |
+--------------------+-------------------------------------------------+
| Suction Specific   | Suction specific speed is a non-dimensional     |
| Speed              | index used to describe the geometry of the      |
|                    | suction side of an impeller, or its NPSHR       |
|                    | characteristics.                                |
+--------------------+-------------------------------------------------+
| Sump               | A basin in which the stormwater is collected    |
|                    | and from which it is pumped out. Sometimes the  |
|                    | terms wet well and sump are used                |
|                    | interchangeably, though some wet wells may have |
|                    | a distinctly separate sump chamber.             |
+--------------------+-------------------------------------------------+
| Sump pump          | A sump pump also called an intake sump or       |
|                    | sludge pump, is designed to remove the solids   |
|                    | and sediment that are conveyed by the storm     |
|                    | water through the inlet conduits into the       |
|                    | storage box.                                    |
+--------------------+-------------------------------------------------+
| System curve       | See System Head Curve                           |
+--------------------+-------------------------------------------------+
| System Head Curve  | A system head curve represents the variation in |
|                    | total dynamic head with pumping rate through    |
|                    | the pumping system. At zero flow, the total     |
|                    | dynamic head is equal to the total static head. |
|                    | As the pumping rate increases, the velocity     |
|                    | head, friction losses, and pump losses          |
|                    | increase. Thus, the total dynamic head          |
|                    | increases with pumping rate.                    |
+--------------------+-------------------------------------------------+
| Total Dynamic Head | Total dynamic head, TDH, represents the total   |
|                    | energy required to raise the liquid from the    |
|                    | intake to the discharge point.                  |
+--------------------+-------------------------------------------------+
| Trash Rack         | A trash rack is a screen that collects debris.  |
+--------------------+-------------------------------------------------+
| Type I Vortex      | Type I vortexes are the start of vortex action  |
|                    | in which tiny bubbles of air are pulled into    |
|                    | the pump. These bubbles are not a significant   |
|                    | impediment to pump performance.                 |
+--------------------+-------------------------------------------------+
| Type II Vortex     | Type II vortexes form for less than thirty      |
|                    | seconds and pull air and floating debris into   |
|                    | the pump. Pump capacity and horsepower are      |
|                    | momentarily affected.                           |
+--------------------+-------------------------------------------------+
| Type III Vortex    | Type III vortexes are continuous and allow      |
|                    | large amounts of air and debris into the pump   |
|                    | accompanied by a sucking noise.                 |
+--------------------+-------------------------------------------------+
| Umbrella           | An attachment to the underside of the pump bell |
|                    | that is used to reduce the submergence          |
|                    | requirements.                                   |
+--------------------+-------------------------------------------------+
| Ungula             | The volume contained in a sloping conduit of    |
|                    | circular cross section below a given horizontal |
|                    | surface                                         |
+--------------------+-------------------------------------------------+
| Usable Storage     | The amount of storage that affects the pump     |
|                    | cycling times. For any given pump, it is the    |
|                    | volume contained between the pump's start and   |
|                    | stop levels less any volume required to convey  |
|                    | flow to the sump.                               |
+--------------------+-------------------------------------------------+
| Valve              | A device to regulate flow through a pipe        |
+--------------------+-------------------------------------------------+
| Vane               | Any of several flat or curved pieces set around |
|                    | an axle and rotated about it moving air, water, |
|                    | etc.                                            |
+--------------------+-------------------------------------------------+
| Velocity Head      | The head that represents the kinetic energy of  |
|                    | flow, described by the term $\frac{V^{2}}{2}g$  |
+--------------------+-------------------------------------------------+
| Volute             | A spiral-shaped casing housing the impeller.    |
|                    | The casing design assures an increase in the    |
|                    | cross-sectional area of flow passages as the    |
|                    | liquid moves through the casing from the        |
|                    | impeller tip, thereby converting flow velocity  |
|                    | to pressure.                                    |
+--------------------+-------------------------------------------------+
| Vortex             | A circulation (swirling) of water from either   |
|                    | the water surface or sump walls.                |
+--------------------+-------------------------------------------------+
| Water Power        | Water Power WP (water horsepower WHP in English |
|                    | units) is the output power of a pump handling a |
|                    | given liquid at a given total dynamic head and  |
|                    | discharge.                                      |
+--------------------+-------------------------------------------------+
| Wet well           | A chamber of the pump station into which the    |
|                    | storm water flows and from which it is pumped.  |
+--------------------+-------------------------------------------------+
| Wet-Pit Station    | A pump station that contains a chamber          |
|                    | (wet-well) into which the storm water is        |
|                    | conducted. The water that accumulates in the    |
|                    | wet-well is discharged by pumps that are        |
|                    | installed in the wet well.                      |
+--------------------+-------------------------------------------------+
| Wire-to-water      | Wire-to-water power is the total electrical     |
| power              | power required to maintain the discharge and    |
|                    | total dynamic head.                             |
+--------------------+-------------------------------------------------+

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A.  []{#__RefHeading___Toc481572159 .anchor}ANNOTATED BIBLIOGRAPHY

***American National Standard for Pump Intake Design*, ANSI/HI 9.8-1998,
Hydraulic Institute, Parsippany, New Jersey, October 1998.**

A recent addition to the Hydraulic Institute standards, this standard
provides guidance and recommendations for the design of a variety pump
intakes for different applications. The standard adopts a different
approach to recommended criteria for sizing intake structures by using
pump bell or pump volute diameter as the primary basis for sizing the
intake rather than discharge rate.

**Anderson, Harold, *Centrifugal Pumps and Allied Machinery*, 4^th^
Edition, Elsevier Advanced Technology, Elsevier Science Publishers Ltd.,
1994.**

This book discusses submersible pumps in general. Particular attention
is paid to the advantages of submersible pumps when compared with
horizontal pumps, motor and bedplate sets. Pump details, materials of
construction, pump characteristics and thrust-bearing loadings are
considered. The book also covers variable speed for centrifugal pumps
and variable flow pumps.

**Baumgardner, Robert H., *Hydraulic Design of Stormwater Pumping
Stations: The Effect of Storage*, Transportation Research Record 948,
National Research Council, National Academy of Sciences, Washington D.
C., 1983, p83.**

This paper provides design guidance for sizing storage facilities used
to reduce peak rates of flow at storm water pumping stations. The effect
of storage is evaluated by using a mass curve routing procedure that
identifies the amount of storage required to reduce the peak rate of
flow to the final discharge rate. The design procedure combines three
independent components: the inflow hydrograph, the stage-storage
relationship and the stage-discharge relationship.

**Brennen, Christopher E., *Hydrodynamics of Pumps*, California
Institute of Technology, Pasadena, California, Concepts ETI, Inc., and
Oxford University Press, 1994.**

This monograph discusses the fluid dynamics of liquid pumps. The focus
is on the "special problems and design issues associated with the flow
of liquid through a rotating machine." Particular attention is made to
cavitation, which is the term used to describe the formation of vapor
bubbles in regions of low pressure within the flow field of a liquid.
Cavitation parameters and inception are discussed (Chapter 5), followed
by chapters describing bubble dynamics, damage and noise (Chapter 6),
pump performance (Chapter 7) and pump vibration due to cavitation
(Chapter 8).

**Brown, S. A., Stein, S. M. & Warner, J. C., *Urban Drainage Design
Manual, Hydraulic Engineering Circular No. 22*, U. S. Department of
Transportation, Federal Highway Administration, Report No.
FHWA-SA-96-078, November 1996.**

This report provides a comprehensive and practical guide for the design
of storm drainage systems associated with transportation facilities.
Pump stations are discussed in Chapter 9. The introduction to chapter 9
is followed by sections on pump station design considerations, design
criteria, determining pump station storage requirements, design
procedure and design philosophy.

**Cheremisinoff, Nicholas P. and Paul N., *Pumps and Pumping
Operations*, Prentice-Hall, inc., 1992.**

This book is intended to assist the reader in making the proper choice,
implementation and use of water pumps and their applications. The book
is divided into six chapters. Chapter 1 considers flow dynamics and
pumping principles. The chapter contains a brief overview of pumps,
pumping operations, support equipment and classes of pumps. Chapter 2
covers pump classification and pumping services in greater detail.
Chapter 3 discusses industrial pumps and their applications including
installation and layout considerations. Oscillating displacement pumps
are discussed in Chapter 4, and system analysis for pumping equipment is
addressed in Chapter 5. The last chapter covers mechanical seals for
pumps.

**Dicmas, John L., *Vertical Turbine, Mixed Flow, and Propeller Pumps*,
Mcgraw-Hill Inc. Book Company, 1987.**

The intention of this book is to provide an overview of all aspects of
vertical diffusion vane centrifugal, or turbine-type pumps in the range
from 1,200 to 13,500 specific speed (0.44 to 5.00 type numbers), which
are commonly referred to as vertical turbine, mixed flow and propeller
pumps. The book provides a useful summary of standard pump
specifications and construction features (Chapter 1) and definition of
terms (Chapter 2). The mechanical design of vertical pumps is discussed
in Chapter 3, followed by chapters on sump design (Chapter 6) and
station design (Chapter 7). Further relevant topics for pump station
design include operation procedures (Chapter 8) and vertical pump drives
(Chapter 5).

**Duan, Ning, *Optimal Reliability Based Design and Analysis of Pumping
Systems for Water Distribution Systems*, Dissertation, University of
Texas at Austin, August 1988.**

This dissertation discusses the optimal reliability based design of
pumps and storage tanks for water distribution systems. New
methodologies are presented for the reliability analysis of pumping
stations and the optimal reliability based design and analysis of
pumping stations for water supply. Included is a reliability analysis of
pumping station storage facility systems (Chapter 4.3.2 and 4.4.2), tank
design (Chapter 6.2-6.3) and reliability concepts such as failure and
repair times (Chapter 2), all of which are important considerations in
the design of pumping stations.

**Garay, Paul N., *Pump Application Desk Book*, published by The
Fairmont Press, Inc., 1990.**

The objective of this book is to bring together the information
necessary to select and apply pumps in systems of all kinds of fluids
and purposes. The book limits itself to a consideration of only those
factors that are necessary for an understanding of pump operation.
Topics covered include pump types and arrangements (Chapters 2 - 4),
pump performance, including NPSH (Chapter 11), pump operating principles
and pumping system parameters. The book also considers the affects of
design variation on use, economy and reliability.

**Germain, James E., et al., *Design of Wastewater and Stormwater
Pumping Stations*, Manual of Practice No. FD-4, prepared by Task Force
on Pumping Stations under the direction of the Facilities Development
Subcommittee Technical Practice Committee, Walter Pollution Control
Federation, Washington D. C. 20037, 1981.**

This important reference provides a practical overview of the wastewater
and stormwater pumping station design process. It is intended as an
outline of the process and as a remainder of the important
considerations involved. The text is divided into nine chapters:

Chapter 1 Introduction

Chapter 2 Station Capacity

Summary of the methods of estimating sanitary wastewater, stormwater and
combined flows. Discussion of the hydraulic design of wet wells.

Chapter 3 Configuration and Design

Discussion of location considerations, station types and structural and
architectural design.

Chapter 4 Mechanical Design

Compilation of the mechanical considerations of pump station design
including installation, screening methods, pumping equipment, and
heating and ventilation.

Chapter 5 Piping Systems

Consideration is given primarily to the piping systems leading into and
out of the pump station. Included is a discussion of the system and
valve hydraulics.

Chapter 6 Electrical Design

Contains a comprehensive description of the electrical equipment that
must be selected and designed for pumping stations.

Chapter 7 Odor Control

The origins and normal odor control practices are covered.

Chapter 8 Appurtenances

A discussion of some of the important accessory equipment in pumping
station design including meters and gauges, seals, pump lubrication,
hoists and ladders, aeration, drainage and safety features.

Chapter 9 Operation

Pump station maintenance and operation are considered.

***Hydraulic Institute Standards for Centrifugal, Rotary and
Reciprocating Pumps*, 14^th^ Edition, Hydraulic Institute, 1983.**

This standard reference is intended to "promote and further the
interests of manufacturers of pumps, as well as the interests of the
public in such matters as are involved in manufacturing, engineering,
safety, transportation and other problems of the (pump) industry"
(Article II, Objects, *By-Laws*). Included are chapters covering
centrifugal, rotary and reciprocating pump standards, materials, and
definitions for hardware terms and for slurry application.

**Jung, Gunter and Schneider, Eugenia, *Design and Optimization of
Seawater Pumping Stations for Industrial Plants*. A paper delivered at
the International Conference on the Hydraulics of Pumping Stations,
Manchester, England, 17 -- 19 September, 1985. Organized and Sponsored
by BHRA, The Fluid Engineering Centre, Paper 14.**

This paper considers the site-specific aspects and number and types of
pumps used at four pumping stations in the Middle East. Reliability and
cost aspects are also discussed.

**Karassik, Igor J., *Pump Handbook*, 2^nd^ Edition, McGraw-Hill Book
Company, 1986.**

This handbook is intended to help in designing, selecting, operating and
maintaining pumping equipment. The handbook discusses first the theory,
construction details and performance characteristics of all the major
types of pumps (Chapters 1 -- 5). Pump drivers, couplings, controls,
valves and the instruments used in pumping systems are discussed in
Chapters 6 -- 8. Pump services are covered in Chapter 9 and intakes and
suction piping in Chapter 10. Chapter 12 discusses installation,
operation and maintenance issues.

**Lever, William F. & Associates, *Manual for Highway Storm Water
Pumping Stations, Volumes 1&2*, Prepared for Federal Highway
Administration, Washington D. C., U. S. Department of Transportation,
Report No. FHWA-IP-82-17, October 1982.**

This manual provides design information for highway storm water pumping
stations. The manual is divided into the following chapters:

Chapter 1 Introduction

Chapter 2 Review of Current Practice

Chapter 3 Site Considerations

Chapter 4 Collection Systems

Chapter 5 Selection of Type of Station and Equipment

Chapter 6 Wet-Pit Design

Chapter 7 Dry-Pit Design

Chapter 8 Pumping and Discharge Systems

Chapter 9 Pumps for Stormwater Applications

Chapter 10 Electric Motors for Stormwater Pumps

Chapter 11 Engines and Accessories

Chapter 12 Electrical Systems and Controls

Chapter 13 Emergency Generators

Chapter 14 Construction Details

Chapter 15 Station Design Calculations and Layouts

Chapter 16 Retrofitting Existing Stations

**Lobanoff, Val S. and Ross, Robert R., *Centrifugal Pumps: Design and
Application*, 2^nd^ Edition, published by Gulf Publishing Company in
association with Plant Engineering, 1992.**

The emphasis of this book is on hydraulic design and is divided into
four parts. Below is a listing of selected topics discussed in each of
the four parts:

Part 1 Elements of Pump Design

-   Introduction

-   Specific Speed and Modeling Laws

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-   Impeller Design

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-   General Pump Design

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-   Volute Design

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-   Design of Multi-Stage Casing

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-   Double-Suction Pumps and Side-Suction Design

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-   NPSH

Part 2 Applications

-   Vertical Pumps

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-   High Speed Pumps

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-   Double-Case Pumps

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-   Slurry Pumps

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-   Hydraulic Power Recovery Turbines

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-   Chemical Pumps

Part 3 Mechanical Design

-   Shaft Design and Axial Thrust

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-   Mechanical Seals

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-   Vibration and Noise in Pumps

Part 4 Extending Pump life

-   Alignment

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-   Bearings and Lubrication

**Lohn, M. B., *The Hydraulics Design Aspects of Three Pumphouses*. A
paper delivered at the International Conference on the Hydraulics of
Pumping Stations, Manchester, England, 17 -- 19 September, 1985.
Organized and Sponsored by BHRA, The Fluid Engineering Centre, Paper
13.**

This paper discusses the factors that determined the location of the
pumphouses and the influence of this location on the pumphouse layout.

**McCuen, Richard H., Johnson, Peggy A. & Ragan, Robert M., *Highway
Hydrology, Hydraulic Design Series No. 2,* Federal Highway
Administration, Washington, D. C., U. S. Department of Transportation,
Publication No. FHWA-SA-96-067, September 1996.**

This publication discusses the physical processes of the hydraulic
cycle, applicable to highway drainage design engineers, and the methods
that are used in the design of highway drainage structures. The
hydrologic methods discussed in the manual include:

-   frequency analysis for analyzing gauged data,

-   empirical methods for peak discharge estimation,

-   hydrograph analysis, and

-   synthesis.

The peak discharge methods discussed include:

-   regression equations,

-   the rational method, and

-   the SCS Graphical method.

Additional methods discussed in the manual include hydrologic methods
used in arid lands, and detailed methods for the planning and design of
detention basins

**Murray, B. G., Ratcliffe, G. A. & Palmer, S., Development Engineering
International Ltd., *Development in Pump Condition Monitoring*, a paper
presented at the Eleventh Technical Conference of the British Pump
Manufacturers' Association: Pump Technology: New Challenges -- Where
Next? Churchill College, Cambridge, England, 18 -- 20 April, 1989.
Published jointly by BHRA (Information Services), The Fluid Engineering
Centre, Cranfield and Springer -- Verlag, Paper 16.**

The objective of this paper is to review some of the recent developments
in machinery condition monitoring, with particular reference to pumping
applications. Particular interest has been shown in three particular
areas due to developments in instrumentation and computer equipment:
Vibration Monitoring, Lubrication Oil Monitoring and Machine Performance
Monitoring. The paper discusses recent developments in each of these
three areas.

**Pollak, F., *Pump Users Handbook (Third edition)*, extracts taken from
an original text by H. Addison, published by Trade and Technical Press
Ltd., England, 1988.**

This handbook emphasizes the importance of selecting the correct pumping
device based upon a correct interpretation of pumping requirements.
Included are detailed accounts of the suction performance of pumps such
as sump design (Sections 3 & 4). Mechanical seals (Section 5b), electric
pump drives and motor starting (Section 8), pipeline systems and valves
(Section 9) and health and safety concerns (Section 13) are also
considered.

**Sanks, Robert L., *Pumping Station Design*, Butterworth Publishers,
1989.**

This is the only reference book available that deals specifically and
comprehensively with the entire subject of the design of all phases of
water and wastewater pumping stations. The first eleven chapters contain
the prerequisites for effective design including hydraulics, piping,
water hammer, electricity and a description of water pumps. Chapters 12
-- 20 consider system design, including pump and driver selection and
general piping layouts for water, wastewater, and sludge pumping. The
last ten chapters discuss appurtenances such as instrumentation and
design, heating and ventilation, noise and vibration, and a comparison
of types of pumping stations and pumps. What follows is the pump station
design process specified by chapter name as given in *Pumping Station
Design.*

Chapter 1 Introduction

Chapter 2 Nomenclature

Chapter 3 Flow in Conduits

Chapter 4 Pipes and Fittings

Chapter 5 Valves

Chapter 6 Fundamentals of Hydraulic Transients

Chapter 7 Control of Hydraulic Transients

Chapter 8 Electrical Theory

Chapter 9 Electrical Design

Chapter 10 Theory of Centrifugal Pumps

Chapter 11 Types of Pumps

Chapter 12 Pump Selection

Chapter 13 Electric Motors

Chapter 14 Engines

Chapter 15 Variable-Speed Pumping

Chapter 16 Pump-Driver Specifications

Chapter 17 System Design for Wastewater Pumping

Chapter 18 System Design for Water Pumping

Chapter 19 System Design for Sludge Pumping

Chapter 20 Instrumentation and Control Devices

Chapter 21 Instrumentation and Control Applications

Chapter 22 Vibration and Noise

Chapter 23 Heating, Ventilating and Cooling

Chapter 24 Designing for Easy Operation and Maintenance

Chapter 25 Preliminary Design Considerations

Chapter 26 Station Layout

Chapter 27 Avoiding Blunders

Chapter 28 Contract Documents

Chapter 29 Costs

**Schall, James, D., & Richardson, Everitt, V., *Introduction to Highway
Hydraulics, Hydraulic Design Series No. 4,* Federal Highway
Administration, Washington, D. C., U. S. Department of Transportation,
Publication No. FHWA HI 97-028, June 1997.**

This publication supercedes the previous HDS 4, *Design of Roadside
Drainage Channels (1965)*. The manual provides an introduction to
highway hydraulics and to hydrologic techniques applicable to small
areas. The hydrologic techniques include the rational equation and an
overview of regression equations. Also included are fundamental
hydrologic concepts, conduit flow principles, and open channel and
closed conduit applications along with examples. The manual provides an
overview of highway drainage design and should be useful to designers
lacking extensive drainage experience.

**Schermel, A., *Multiple Pump Wet Well Intake and Pumping Station
Design at Ontario Hydro-Nuclear Generating Stations*. A paper delivered
at the International Conference on the Hydraulics of Pumping Stations,
Manchester, England, 17 -- 19 September, 1985. Organized and Sponsored
by BHRA, The Fluid Engineering Centre, Paper 16.**

The water intake, pumping station and discharge structure designs for
three nuclear generating stations are described. Associated economical
and environmental constraints are discussed.

**Sinclair, M. R. & Bjorkander, G., *A New Approach to the Design of
High Capacity Storm and Foul Pumping Stations,* a paper presented at the
Eleventh Technical Conference of the British Pump Manufacturers'
Association: Pump Technology: New Challenges -- Where Next? Churchill
College, Cambridge, England, 18 -- 20 April, 1989. Published jointly by
BHRA (Information Services), The Fluid Engineering Centre, Cranfield and
SPRINGER -- VERLAG, Paper 5.**

This paper will show that the adoption of a larger number of lower
capacity submersible pumps, installed directly in a wet wall, with
individual siphonic discharge into a surge chamber, can result in
significant reductions in capital plant, construction and energy costs,
reduced hydraulic and electrical supply transients and improved
flexibility of operation and maintenance procedures.

**Stewart, Harry L., *Pumps*, revised by T. Philbin, Bobbs-Merill Co.,
Inc., 1984.**

The purpose of this reference is to describe and provide a better
understanding of the fundamental and operating principles of pumps, pump
controls and hydraulics. Types of pumps considered are Centrifugal,
Rotary, Reciprocal and Special Service Pumps. The chapters on hydraulics
include discussions of hydraulic principles (Chapter 3), accumulators
(Chapter 7), power tools (Chapter 9), cylinders (Chapter 10), control
valve operations (Chapter 12) and fluids (Chapter 13).

**United States Army, Corps of Engineers, *Texas -- Cocodrie Pumping
Plant, Red River Backwater Area, Tensas Basin, Louisiana Fish and
Wildlife Mitigation Plan*. Communication from the Assistant Secretary of
the Army (Civil Works), U. S. Government Printing Office, Washington D.
C., 1979.**

The volume is a compilation of various correspondences and reports
submitted by the U. S. Army Corps of Engineers discussing the proposed
construction of a water pump station in the Tensas Basin. The documents,
which consider the environmental concerns raised by the construction of
the pumping plant and provide a thorough review of the mitigation
process and other related environmental issues, are a valuable source of
information in considering a site for a pumping station.

**Walker, Roger, *Pump Selection* -- *A Consulting Engineer's Manual*,
Ann Arbor Science Publishers, Inc., 1972.**

This book is intended to facilitate the selection of pumping equipment
for water supply systems. Section 1 is concerned with the selection of
pumping equipment. Section 2 describes suction and discharge conditions
including discussions of NPSH, TDH, cavitation and system head curves.
Section 3 discusses specifications including shaft speed, performance
curves, stuffing boxes, mechanical seals, valves and piping, and pump
drivers. Section 4 considers maintenance requirements.

**Warring, R. H., *Pumping Manual,* 7^th^ Edition, Trade & Technical
Press Limited, 1984.**

The *Pumping Manual* is considered the best source for practical
information and data on the selection, installation, operation, and
maintenance of industrial pumps, in every field of application. The
manual has three sections. Section 1 has a general introduction and
discusses pump principles and pump performance. Section 2 is divided
into five parts. The sections discuss pump types and characteristics,
duty pumps, pump construction, pumping practice and pump ancillaries,
respectively. Section 3 covers pump services and applications.