Diaphragm Pump Explained

DIAPHRAGM

PUMP EXPLAINED

HANDBOOK

Second Edition, 2025

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Table of Contents

What is a diaphragm pump? .................................................................................................... 1

What are the main parts of a diaphragm pump? ................................................................. 1

How does a diaphragm pump work?...................................................................................... 2

Diaphragm Pump Operation ................................................................................................... 3

Diaphragm Pump Construction Materials ............................................................................. 4

Diaphragm Pump Advantages and Disadvantages .............................................................. 4

3D Model Annotations .............................................................................................................. 5

Non-return Valve ................................................................................................................... 5

Suction ..................................................................................................................................... 5

Discharge ................................................................................................................................ 5

Diaphragm Membrane ......................................................................................................... 6

Pneumatic Valves ................................................................................................................... 6

www.saVRee.com Diaphragm Pump Explained| pg. 1

What is a diaphragm pump?

A diaphragm pump is a type of positive displacement pump that uses a flexible

membrane (diaphragm) as its primary pumping element to move and pressurise a fluid.

Diaphragm pumps are used for low pressure, low flow, applications, and can be used

to pump many types of gases, liquids, and slurries.

Diaphragm Pump

Good to know – the diaphragm pump gets its name from the diaphragm that it uses to pump

fluid. Pumps are often named after the part of the pump that causes the pumping action e.g.

gear pump, piston pump etc.; the same is true for valves, which are usually named after the

disc that is used to open and close the valve e.g. ball valve, gate valve, etc.

What are the main parts of a diaphragm pump?

A diaphragm pump is composed of relatively few main parts, these are:

Non-return valves (suction and discharge)

Pumping chamber

Diaphragm

Suction manifold

Discharge manifold

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Diaphragm Pump Parts

Diaphragm pumps are typically pneumatically operated, but may also be electrically or

mechanically operated. Electrically operated pumps require electric motors whilst

pneumatically operated pumps require an air distribution valve. This article focuses

upon air actuated diaphragm pumps because they are the most common.

Good to know – ‘non-return’ valves are also known as ‘check’, ‘one-way’, ‘reflux’, ‘foot’ and

‘retention valves’, but all terms mean the same thing!

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How does a diaphragm pump work?

Diaphragm pumps require compressed air, electrical current, or mechanical

movement in order to work; the following example assumes compressed air is used as

this is the most common medium used to operate a diaphragm pump. It is possible to

have a single or double diaphragm pump, but the double diaphragm pump is far more

common due to its higher efficiency (a result of its double acting motion).

Good to know – double acting pumps discharge fluid whilst moving in two directions

(bidirectional). Single acting pumps discharge fluid whilst moving in only a single direction

(uni-directional). Hydraulic pistons and pneumatic rams often utilise a single or double

acting design.

www.saVRee.com Diaphragm Pump Explained| pg. 3

Single and Double Acting Pumps

Diaphragm Pump Operation

Compressed air (typically 6-7 bar/87-101psi pressure) is connected to a double

diaphragm pump via hoses or piping. A pneumatic piston (air distributor) delivers

compressed air to the space behind one of the diaphragms whilst air is simultaneously

exhausted from the other; this is made possible because both diaphragms are mounted

on a common shaft i.e. when one moves, so does the other. Exhausted air is usually

discharged through a muffler to make the pump operate quieter and to eliminate a high

pressure jet of air being intermittently discharged from the pump.

If air is being exhausted, the affected diaphragm contracts and obtains a concave shape.

If air is being supplied, the affected diaphragm expands and obtains a convex shape. As

the diaphragm changes shape, a positive pressure (convex shape), or negative

pressure (concave shape) is created within the pumping chamber. Fluid is sucked into,

or discharged from, the pump, due to the pressure differences created within the

pumping chambers. Non-return valves are used to ensure that flow through the pump

only occurs in one direction.

www.saVRee.com Diaphragm Pump Explained| pg. 4

Diaphragm Pump Operation

Diaphragm Pump Construction Materials

The pump casing is often manufactured from aluminium or some sort of polymer

based material e.g PTFE; aluminium makes the pump light whilst polymer materials

make the pump corrosion resistant.

Diaphragms can be manufactured from rubber, thermoplastic elastomer (TPE) or

polytetrafluoroethylene (PTFE).

Diaphragm Pump Advantages and Disadvantages

Diaphragm pumps are very versatile and are consequently used in many different

industries for many applications; they are:

Well suited to operate in corrosive environments, or pump corrosive fluids,

since their parts can be chosen to be corrosion resistant.

Can be manufactured to be intrinsically safe i.e. the pump is not a source of

ignition when placed within an explosive or flammable environment.

Can operate even if partially or fully submerged (providing the air exhaust is

above the surface of the submerging liquid).

Are self-priming (positive displacement pumps are self-priming, thus so are

diaphragm pumps).

Due to their size, these pumps are lightweight and portable.

www.saVRee.com Diaphragm Pump Explained| pg. 5

Contain few parts and require little maintenance.

Good to know – the term ‘self-priming’ means that a pump has the ability to pump air.

3D Model Annotations

Non-return Valve

Non-return valves allow flow in only one direction. As the diaphragm moves, the

pressure created within the casing will either lift the ball off its seat and allow flow, or,

press the ball against its seat and stop flow. The effect the diaphragm has upon each

valve depends upon the orientation of the non-return valve (the upper non-return valve

operates in the reverse direction to the lower non-return valve).

Swing Check Non-return Valve

Suction

Fluid enters the pump through this connection. Diaphragm pumps are positive

displacement pumps; thus they can pump gas, liquid or vapour.

Discharge

Fluid is discharged from the pump through this connection.

www.saVRee.com Diaphragm Pump Explained| pg. 6

Diaphragm Membrane

The diaphragm is actuated via a pneumatic piston. When pneumatic pressure is applied

to one side of the piston, the diaphragm changes to a concave shape. When pneumatic

pressure is applied to the other side of the piston, the diaphragm changes to a convex

shape. As the diaphragm changes shape, a positive (convex) or negative (concave)

pressure is created between the two non-return valves; fluid is sucked or discharged from

the pump due to the pressure difference created. Diaphragm membranes are typically

constructed of thick rubber material.

Pneumatic Valves

Pneumatic valves within the diaphragm casing distribute air to either side of the piston.

As air is distributed to each side of the piston, the piston direction changes, and so too

does the shape of the diaphragm (convex to concave etc.).

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