Diaphragm Pumps Information 

Image Credit: All-Flo Pump Company, LLC. | Grainger Industrial Supply | Vacuubrand GMBH + CO KG

Diaphragm pumps are positive displacement pump which move gases, liquids, or gas-liquid mixtures via a 

reciprocating diaphragm. They are highly reliable because they do not include internal parts that rub against each 

other. They also contain no sealing or lubricating oils within the pumping head, meaning there is no chance of oil 

vapor leakage or contamination of the handled media.

Advantages Disadvantages

 Seal-less and oil-free  Low maximum speed

 Self-priming up to 6 meters  Not very energy efficient

 Simple cleaning/maintenance  Pulsed flow - requires dampener for reduction

 Versatile design and function (can handle most media types)

 Can run dry for short periods

Pump Composition 

Simple diaphragm pumps consist of a diaphragm, displacement chamber, two valves, and a driving mechanism. The

diaphragm is made of a flexible material compatible with the pumped media. It is sealed in place between the side of

the displacement chamber and an attached flange. The chamber's volume is slightly greater than what the diaphragm

can displace. The valves are typically spring-loaded ball valves or flapper valves made of the same material as the

diaphragm, and they function to admit the fluid in and out of the chamber. The driving mechanism is what flexes the

diaphragm - in the diagram below, the drive mechanism is a spring activated by a solenoid.
Diagram of solenoid diaphragm pump. Image Credit: Honda-varadero-uk.org

Pump Operation 

Diaphragm pumps are positive displacement pumps, meaning they use contracting and expanding cavities to move

fluids. For more information about this category of pumps, visit the Positive Displacement Pump Selection

Guide page on GlobalSpec.

Diaphragm pumps work by flexing the diaphragm out of the displacement chamber. When the diaphragm moves 

out, the volume of the pump chamber increases and causes the pressure within the chamber to decrease and draw in 

fluid. The inward stroke has the opposite effect, decreasing the volume and increasing the pressure of the chamber to 

move out fluid. This operation is very similar to the draw in, push out, concept of human breathing.

The motion of the diaphragm looks like this:

Image Credit: animatedsoftware.com

This video provides further demonstration:

Video Credit: PrecisionPlus

Types 

Diaphragm pumps can be classified based on their drive mechanism and whether they are single or double acting.

Drive Mechanisms 

The diaphragm in diaphragm pumps can be driven by a number of different mechanisms.
 Mechanical - These pumps are operated using a simple and robust reciprocating mechanical linkage directly

attached to the diaphragm. This is typically a crank or gear mechanism which converts motor rotation into

reciprocating motion of the linkage (spring, piston, plunger) attached to the diaphragm. Flow is adjusted by

changing the stroke length or the pump speed. These pumps have similar characteristics to piston pumps and

plunger pumps.

 Hydraulic - These pumps implement an intermediate hydraulic fluid on the opposing side of the diaphragm. 

The fluid is pressurized by a plunger or piston in order to flex the diaphragm. These operate similarly to 

mechanical pumps, but the hydraulic fluid contacts the diaphragm rather than a mechanical linkage. Flow is 

varied by adjusting pump speed or the amount of contained hydraulic fluid.

 Solenoid - These pumps have an electric motor that controls a solenoid magnet. When activated, the solenoid 

creates a magnetic force which interacts with a ferro-magnetic metal part on the diaphragm, causing it to flex. 

Flow is adjusted by changing the pump speed.

 Air - These pumps are double-acting (double diaphragm) pumps which use compressed air to drive two 

separate diaphragms alternatively. The air flow is alternated between diaphragms via a shuttle valve. Flow is 

changed by adjusting the air pressure supplied to the pump.

Single or Double Action 

The action of a diaphragm pump refers to how many diaphragms and sets of valves the pump incorporates.

 Single acting pumps incorporate one diaphragm and one set of valves, and are characteristic of mechanical 

drive pumps.

 Double acting pumps, also known as double diaphragm pumps, incorporate two diaphragms and two sets of

valves. Air-operated diaphragm pumps are characteristically double-acting. For more information on

specifically selecting double diaphragm pumps, visit theDouble Diaphragm Pumps Selection Guide on

GlobalSpec.

Design 

Some manufacturers design pumps to the specific needs of a customer's application. In these cases, it is especially 

important for the buyer to understand how the pump design affects performance.

Pump Stroke 

The pump stroke length is the principal factor defining a pump's capacity and pressure ratings. Higher offset (longer 

stroke) produces higher flow rates and greater pressure/suction per stroke.

Diaphragm 

The diaphragm is the main determinant of a diaphragm pump's performance, and must be sized to coincide with the 

desired pump stroke. Three different characteristics define a diaphragm's design.

 Durometer - Measures the stiffness of the diaphragm elastomer. Higher durometer means a harder diaphragm 

which can generate higher pressures and flows. Lower durometer diaphragms product are rated for lower 

pressures and require less energy to operate.

 Shape - Determines the flow and pressure level of the pump. Shapes include flat, rolled (molded), and 

structured types.

 Flat - Inexpensive and can provide adequate vacuum separation between chambers, but has a limited 

stroke/offset length and lower energy efficiency. It also has a lower lifespan since it tends to deform as it adjusts 

to the stroke.
 Rolled/molded - Shaped to factor in the required stroke length, it provides a repeatable displacement with a 

constant effective pressure area. It has a longer life than the flat type and creates less resistance (higher 

efficiency) but is more expensive.

 Structured- Patented diaphragm design that incorporates a ribbed underside to accommodate a specific load. 

Provides higher strength, good capacity, and higher efficiency than other types in a small size

Image Credit: Design World - KNF Neuberger Inc.

 Materials - The flexible material of the diaphragm. The industry standard is EPDM rubber (ethylene propylene 

diene monomer). Other materials include PTFE (polytetrafluoroethylene), rubber, and other plastics 

and elastomers. Material affects the diaphragms lifespan, stiffness (durometer), and resistance to chemical or 

environmental corrosion.

System 

The design of the corresponding valves and the motor which powers the pump also are important factors to consider.

 Valves - Parameters include shape, materials (compatible with the pumped fluid), and durometer (affects flow 

and noise level).

 Motor - The motor must be compatible with the energy requirements of the pump. In addition to meeting the 

pump's needs, the RPM and torque of the motor affect the pump's stalling pressure, energy efficiency, and noise 

level.

Materials 
Pumps are typically designed with a number of different materials. The base materials, which constitute the parts of 

the pump exposed to the pumped media and the outside environment, are the most important to consider. Fluid 

characteristics, pressure ratings, and operating environment factors should be considered when selecting these 

materials (Images Credit: Direct Industry).

 Cast iron provides high tensile strength, durability, and abrasion resistance 

corresponding to high pressure ratings.

 Plastics are inexpensive and provide extensive resistance to corrosion and chemical 

attack.

 Steel and stainless steel alloys provide protection against chemical and rust

corrosion and have higher tensile strengths than plastics, corresponding to higher pressure ratings. 

 

Other materials used in pump construction include:

 Aluminum

 Brass

 Bronze

 Ceramics

 Nickel-alloy

The Pump Features page on GlobalSpec provides more information on pump material characteristics and other 

features.
Specifications 

The primary specifications to consider when selecting diaphragm pumps are flow rate, pressure, horsepower, power 

rating, and operating temperature. Information on interpreting these specifications can be found on 

GlobalSpec's Pump Flow page.

Design tip: Diaphragm life can be significantly prolonged by maintaining lower diaphragm temperatures. Pumps 

designed with additional fan cooling, especially those directed over the pumping head surface, can reduce 

unnecessary heat exposure and buildup.

Media Type 

Selecting the right pump requires an understanding of the properties of the liquid in the addressed system. These

properties include viscosity and consistency.

 Viscosity is a measure of the thickness of a liquid. Viscous fluids like sludges generate higher systems pressures

and require more pumping power to move through the system. Diaphragm pumps are designed to handle both

viscous and thin liquids.

 Consistency is the material makeup of the liquid solution in terms of chemicals and undissolved solids. Positive

displacement pumps like diaphragm pumps are generally better suited for handling these solids, but dynamic

pumps which are designed correctly (i.e. with certain impeller blades) can handle them as well. Solutions with

corrosive chemicals should be handled by pumps with materials and parts designed to withstand corrosion.

Applications 

Diaphragm pumps are commonly called "mud hogs" and "mud suckers" because of their use in pumping slurries

and wastewater in shallow depths. They are capable of handling all sorts of aggressive media including gases and

gas/liquid mixtures, and can achieve very high pressures. They should not be used to pump dangerous or toxic gases,

since diaphragm pumps are not hermetically sealed.

Larger models of this pump type are used to move heavy sludge and debris-filled wastes from trenches and catch

basins, applications where centrifugal pumps perform poorly due to high discharge volumes and low water levels

which would cause them to lose their prime.

Smaller models are typically used in chemical metering or dosing applications where very constant and precise

amounts of liquid delivery are required.

References 

KNF Pumps & Systems - Diaphragm Pumps (pdf)

Pump Scout - Diaphragm Pumps

Related Products & Services 

 DC Powered Pumps

DC powered pumps use direct current from motor, battery, or solar power to move liquids such as acids, 

chemicals, lubricants and oil, as well as water, wastewater, and potable water.

 Dosing Pumps

Dosing pumps are low-volume fluid pumps with controllable discharge rates used to inject additives into the 

mixing or pumping system.
 Magnetic Drive Pumps

Magnetic drive pumps are sealless pumps that use a coaxial magnetic coupling to transmit torque to an impeller. 

A standard electric motor drives a set of permanent magnets that are mounted on a carrier or drive assembly.

 Plastic Pumps

Plastic pumps are designed to move fluids that would corrode or damage other types of pumps. They provide 

broad chemical resistance and are less costly and lighter in weight than metal pumps.

 Positive Displacement Pumps

Positive displacement pumps use a mechanical force such as gears, bladders, pistons, plungers or diaphragms to 

push liquid through and out of the pump.

 Sanitary Pumps

Sanitary pumps are used to transport and meter solutions, slurries, and colloids of food and agricultural 

materials in operations such as food processing that require cleanliness. There are four basic types of sanitary 

pumps: centrifugal, positive displacement, jet, and airlift.

 Syringe Pumps

Infusion or withdrawal syringe pumps provide high pressure and high accuracy for applications such as high 

performance liquid chromatography (HPLC). Used to deliver precise amounts of fluid at specific time 

intervals.

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