# Presentation: 247494

## Vehicle-Tank Metering SystemsOperation & Design

- Vehicle-Tank Meters
- NIST Short Course

## Objectives

- Identify key elements of VTM liquid- measuring device systems
- Describe principle of “Positive Displacement” liquid measuring

## Vehicle-Tank Metering Systems

- Variety of designs of VTM LMD’s
- new technology & advances
- Intended to help you understand _**typical**_ features, not specific makes and models
- Accuracy depends on the operation of the _**whole system**_, not just on the meter itself
- Will look at:
- intake line
- measuring and indicating elements
- discharge elements
- control elements

## Figure 2-1:The Vehicle-Tank Metering System

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## Figure 2-3: Power-Operated System

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## Typical Pump Designs

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## Pump Operation

- Pump draws product from tank and propels it toward meter
- provides pressure required to deliver product
- usually driven by truck engine through linkage controlled by operator
- rate of displacement is a function of:
- size of the piping at the outlet
- pump speed and design

## Pump Speed

- can be a critical element in measurement accuracy
- if too high, pressure at the inlet falls below the vapor pressure of the product
- causes some vaporization
- technical term for this vaporization is **“cavitation”**
- often called “flashing”
- results in some degree of overregistration
- right size and speed of pump help avoid “cavitation”

## Typical Vapor Eliminator

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## Vapor Eliminator--Functions

- removes vapor prior to the meter
- last line of defense against vapor caused by restrictions, etc.
- Basic operation
- float in chamber of air eliminator
- liquid flows into chamber and vapor bubbles rise to the surface
- when float drops below a certain level, valve opens to vent vapor
- vapor carried back to vapor space of storage tank
- as vapor is removed, level of liquid flowing in rises & valve closes
- cycle begins again
_**entrained**_ air very difficult to remove

## Other System Components

- _Strainers_
- trap solid contaminants
- must be kept clean to avoid restrictions & vapor production
- _Piping and Valves_
- suitable length of piping & proper fittings
- reduces friction
- reduces cavitation

## Positive Displacement Meters

- liquid momentarily separated into _segments of known volume_
- same number of segments pass through meter on each revolution
- _segments are rejoined_ after the meter and flow to the discharge line
- fluid flow drives meter’s moving parts
- volume is determined from number of meter revolutions & the quantity per revolution

## Other Metering Technologies

- Turbine
- Mass Flow
- Other

##  PD Meter Design - Example 1

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##  PD Meter Design - Example 2

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## PD Meter Design - Example 3

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## Meter Errors

- simple design means relatively few causes
- typical causes:
- presence of vapor in product
- solid contaminants
- widens clearances
- this is why strainer is important
- small amounts of slippage
- can be offset by meter adjustment to some extent
- increased at low flow rates

## Figure 3-8:Mechanical Indicator

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## Mechanical Registers

- wheel type:
- series of wheels
- one wheel per digit
- wheel segmented with numbers & lines
- revolving meter shaft
- gear train transfers revolution of meter to the indicating elements (to right-hand wheel)
- right-hand wheel turns with meter shaft
- each complete revolution of right-hand wheel increments next higher wheel
- fixed indicator--pointer

## Figure 3-7:Right Hand Indicating Wheel

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## Figure 3-12:Electronic Indicator

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## Electronic Indicators

- fewer moving parts
- often more features and information:
- computing capability
- multiple calibration points
- data communication
- mechanical motion of the shaft is transferred into a digital signal
- accomplished by means of a pulser

## Pulsers for Electronic Indicators

- different kinds of pulsers
- switch closed--current flows;switch open--current stops
- pulser can produce from 10 to 1,000 discrete pulses per revolution of the meter
- register counts the pulses and produce digital display

## Definition - Analog Type

- _Analog_:
- 	analog type.  A system of indication or recording in which values are presented as a series of graduations in combination with an indicator, or in which _the most sensitive element of an indicating system moves continuously during the operation of the device_. [1.10]

## Definition - Digital Type

- _Digital_:
- 	digital type.  A system of indication or recording of the selector type or one that advances intermittently in which all values are presented digitally, or in numbers.  In a digital indicating or recording element, or in digital representation, _there are no graduations_. [1.10]

## Figure 3-11:Electronic and Digital Indicators

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- analog shows quantities between graduations
- digital does _**not**_ show intermediate quantities
- analog and digital can both be designed to meet the sensitivity required

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## Other Device Features -	 Reset

- returns indications to zero (per H44)
- knob on an analog
- pushbutton on a digital
- cannot display values during the reset operation when values _advance_ to zero
- do not want readable values during reset
- shutters or blanking are used

## Mechanical Indicator Reset(from Figure 3-8)

**Reset**

**Shutters drop to obscure**
**indications during reset**

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## Electronic Indicator Reset(From Figure 3-12)

**Reset**

**Indications blank during**
**reset operation**

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## Other Device Features - Totalizers

- totalizers keep track of total product
- used for:
- inventory control
- detect theft & loss
- testing

## Meter AdjustmentsThrough the Indicator

- register “counts” number of meter revolutions
- can’t change quantity per revolution
- so, change amount indicated per revolution
- register is adjusted to bring the _indication_ of the delivery as close as possible to a zero-error condition
- excessively worn meter may not be capable of adjustment

## Meter Adjustments (cont.)

**Adjustments through **_**digital**_** indicators:**
- performed electronically
- calibration factors based on errors observed during testing
- some have multiple point calibration
**Adjustments through **_**mechanical**_** indicators:**
- “change gear” mechanism in some models
- rate of revolution is altered by changing gears
- another design adjusts the speed of the output shaft to the register over a range
- may use a calibrated dial to accomplish this

## Ticket Printer

- _required_ for all vehicle-mounted systems (UR.2.2.)
- requirement became _retroactive in January 1994_
- exception for aircraft refueling & for aircraft-related operations (UR.2.2.1.)
- driven directly by the register:
- mechanically or electronically
- some have capability to print prices, tax, dates, etc. calculated by the register

## Discharge Line or Hose

- carries metered product to the receiving tank
- “wet hose” system
- i.e. full of liquid at all times
- shut-off valve at end to prevent hose from being drained
- “dry hose” system
- designed to be drained after every delivery

## Summary

- I)	A number of elements comprise VTM measuring systems
- II) Intake Line
- Carries product from storage tank to the meter
- Includes:
- 	a) system pump
- 	b) several automatic and manual flow-controlling devices
- 	c) vapor eliminator
- 	d) strainers
- 	e) valves
- III) Meter
- most are positive displacement
- segment known volume of product

## Summary

- IV) Indicating Elements
- mechanical and electronic
- definitions:  analog/digital
- reset
- totalizers
- meter errors are corrected by adjustments that affect the registration of product processed per meter cycle
- V) Other accessory devices may be included
- ticket printer
- VI) Discharge Line
- VII) Additional Accessory Devices