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
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).
Diaphragm Pump Animation
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.
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.
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.
- 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.
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.).
Additional Resources
https://www.tacmina.com/learn/basics/01.html
https://www.verderliquids.com/us/en/pumps-by-principle/diaphragm-pump/how-do-diaphragm-pumps-work