Piston pumps are among the oldest and most versatile pump designs. They generate high pressures and deliver a very consistent volume per stroke. In many industrial applications, however, the question is: piston pump or diaphragm pump? This guide explains how a piston pump works, how it is built and which types exist – and shows when an air-operated double diaphragm pump (AODD pump) is the more economical solution.
In short: A piston pump (also called a reciprocating pump) is an oscillating positive displacement pump. A piston moves back and forth inside a cylinder, draws in liquid on the return stroke and pushes it into the discharge line through a valve on the forward stroke.
How does a piston pump work?
The working principle of the piston pump is based on two strokes:
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Suction stroke: The piston moves out of the cylinder. A vacuum forms in the cylinder chamber, the suction valve opens and liquid flows in. The discharge valve stays closed.
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Discharge stroke: The piston moves into the cylinder. Pressure rises, the suction valve closes, the discharge valve opens and the fluid is pushed into the discharge line.
Because the same volume is displaced with every stroke, the flow rate is almost independent of the back pressure. The flow is pulsating, however – more so with single-acting pumps than with double-acting or multi-cylinder designs.
Design of a piston pump
| Component |
Function |
| Cylinder |
Working chamber in which the fluid is displaced |
| Piston or plunger |
Moving displacement element |
| Piston seal / packing |
Seals the piston against the cylinder – wear part |
| Suction and discharge valve |
Check valves (ball, disc or cone) that control the flow direction |
| Drive |
Electric motor with crank drive, air motor, solenoid or hand lever |
Types of piston pumps
Reciprocating piston pump with crank drive
The classic design: a motor drives the piston via crankshaft and connecting rod. Multi-cylinder plunger pumps reach very high pressures, for example in high-pressure cleaners or process plants.
Pneumatic piston pump
Here an air piston drives the pumping piston directly. Different piston areas create a pressure ratio, so the pump delivers a multiple of the air pressure at the outlet. Pneumatic piston pumps are therefore often used for greases, sealants and airless spraying.
Oscillating piston pump (vibration pump)
A solenoid makes an armature with a piston oscillate – usually at mains frequency. These pumps are small and inexpensive and are found in coffee machines, cleaning devices and small appliances. They are generally not designed for continuous industrial duty with chemicals.
Inline piston pump
Several pumping elements are arranged in a row and actuated by a camshaft. This design is best known from fuel injection in diesel engines.
Piston metering pump and piston diaphragm pump
Piston metering pumps deliver precisely defined volumes per stroke and are used for dosing. In a piston diaphragm pump, the piston moves a hydraulic fluid, which in turn deflects a diaphragm – so the pumped fluid never touches the piston. This is typical for process metering pumps.
Piston air pump
The simplest form is the piston air pump, such as a bicycle pump: piston, cylinder and check valve compress air instead of liquid. The principle is the same.
Piston pump applications
- High-pressure applications (cleaning, water jetting, test benches)
- Precise dosing of additives and chemicals
- Grease and lubricant transfer, sealants, airless spraying
- Fuel injection, hydraulics
Piston pump vs. air-operated diaphragm pump
The air-operated diaphragm pump is also an oscillating positive displacement pump. Instead of a piston, two diaphragms do the work and separate the fluid completely from the drive. More on this in our guides for diaphragm pumps.
| Criterion |
Piston pump |
Air-operated diaphragm pump |
| Achievable pressure |
Very high (up to several hundred bar, depending on design) |
Up to approx. air pressure; correspondingly higher with 2:1 high-pressure version |
| Dosing accuracy |
Very good |
Good, but pressure-dependent |
| Abrasive fluids, solids |
Critical – piston seal wears |
Well suited, no sliding seals in the fluid |
| Dry running |
Usually not permitted |
Can run dry without damage |
| Running against a closed valve |
Pressure relief valve required |
Pump simply stalls |
| Self-priming |
Yes |
Yes, even dry |
| Explosion protection |
Depends on the drive |
No electrics, ATEX versions available |
| Maintenance |
Seals, valves, drive |
Diaphragms and valves, easy to replace |
When is a piston pump the better choice?
If you need very high pressures or have to dose to the millilitre, a piston or piston diaphragm pump usually has the edge.
When is an air-operated diaphragm pump the better choice?
For transferring, pumping and emptying chemicals, paints, slurries, wastewater or viscous fluids, the AODD pump plays to its strengths: no piston seal in the fluid, safe to run dry, tolerant of solids and usable in hazardous areas without electrics.
Frequently asked questions
What is a reciprocating pump?
A reciprocating pump is a positive displacement pump in which a piston, plunger or diaphragm moves back and forth. Piston pumps, plunger pumps and diaphragm pumps all belong to this group.
How much pressure can a piston pump generate?
That depends on design, piston diameter and drive power. Simple pumps work at a few bar, plunger high-pressure pumps at several hundred bar.
Is a diaphragm pump a piston pump?
No, but both are oscillating positive displacement pumps. In a diaphragm pump a flexible diaphragm takes over the role of the piston and hermetically separates fluid and drive.
Not sure which pump suits your fluid? Tell us the fluid, flow rate and head – we will recommend the right Versamatic® air-operated diaphragm pump.
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