Is it better to paint spray with a diaphragm pump or piston pump? Talking with customers, we often hear this question.

The answer to this is not very simple and depends on the needs of the customer and the area of application.

Both piston pumps and diaphragm pumps are designed for specific purposes and both can achieve good results.

For this reason, we discuss in the following article some of the advantages and disadvantages of diaphragm and piston pumps.

What a diaphragm pump looks like on the inside

Technical design of diaphragm and piston pumps

Diaphragm and piston pumps differ in design and operation, so here is a brief technical outlook.

Design and function of a diaphragm pump

A plastic diaphragm generates rapid pressure and is generally powered by an electric motor, but there are also pumps operated by compressed air. In addition, an inlet valve and an outlet valve ensure the control of the pressure and a uniform material flow.

The desired operating pressure is regulated via a control valve. The design is therefore very simple. Further electronic components are not installed.

Because of this simple design diaphragm pumps, unlike electric piston pumps, have no mechanism for detecting the pressure requirement and therefore operate as a “permanent rotor”. The pump is therefore running non-stop as it is switched on.

Diagram of a Wagner diaphragm pump

Design and function of a piston pump

An electric piston pump is more complex in construction than a diaphragm pump. These pumps are also generally powered by an electric motor (there are also air-operated models however). By the piston stroke, ie, the movement of the piston, the paint is sucked in.

Also with this pump type, valves ensure uniform material flow. As with the diaphragm pump, the piston pump also has a pressure regulating valve to obtain the desired working pressure.

In contrast to the diaphragm pump, which functions as a “permanent rotor”, electric piston pumps detect the set operating pressure (eg 120 bar). The pump operates up to this pressure range, the motor switches off as soon as the desired working pressure has been reached.

And while spraying, as the pressure drops, the piston pump immediately detects the pressure drop and begins pumping the material until the desired pressure range is reached.

A typical piston for a piston pump

In order to implement this intelligent pump technology, an electronic control is necessary, which constantly measures the pressure via a pressure sensor and transmits this information to the “electronic brain” of the paint sprayer, the circuit board.

From there, the respective command is passed on to the engine. The engine starts up when more working pressure is required and switches off when the desired pressure range of, for example, 120 bar is reached.

Other electronic components such as digital displays or even remote controls are usually installed on electronic piston pumps for monitoring and control purposes.

Advantages and disadvantages of diaphragm and piston pumps

Now that we know how the pumps operare, what are the advantages and disadvantages of the diaphragm and piston pumps? Here there are many arguments to consider. Some of these are addressed in the following section, including the question of wear, cost of purchase, maintenance and repair. In addition, the technical advantages and disadvantages as well as some application examples are examined.

Wear and tear

As we mentioned above, Airless diaphragm pumps are “permanent rotors” which pump non-stop, whereas piston pumps only work when pressure is required. This should result in a higher wear on the components of diaphragm pumps since the mechanical stress on the components is higher than for the “smart pump”.

A seemingly strong argument for a piston pump as a paint spraying device, but it is not that simple. Even if the wear on some components of piston pumps is lower, a membrane pump is much simpler.

Many components installed on a piston pump do not exist at all on a diaphragm pump. Components that do not exist can not be broken. This applies in particular to electronic components on piston pumps such as the circuit board, the pressure sensor and the digital display for pressure display.

Cost of maintenance and repair

Similar to the consideration we have just made above. A diaphragm pump in subject to higher wear on its components, hence a higher risk of damage through constant mechanical strain. However, the diaphragm pump is simply constructed.

This makes it easier to maintain and repair, and minor problems can be solved by the users themselves. Electric piston pumps have a lot more electronic components, which usually have to be changed in the event of damage by a professional and are often very expensive.

Particularly serious is a circuit board damage, which easily can lead to costs of several hundred euros and with larger Airless devices also the thousand euro mark can be reached.

Price difference

Diaphragm pumps are mainly available from Wagner, but also FARBMAX has many diaphragm pumps.

Graco only offers piston pumps, which can of course also be obtained from other manufacturers such as Wagner, Storch, Titan or FARBMAX.

Diaphragm and piston pumps are available at comparable prices in the entry-level segment as well as in the upper quality range.

Applications

Depending on the application, diaphragm or piston pump can offer advantages and disadvantages, so here we will be examining some areas of application and materials to work out what’s best.

Lacquers and small quantities of material in general

When processing lacquers, glazes and in general small quantities of material, diaphragm pumps probably have a slight edge over piston pumps. The material in usually put in from above into the spraying unit. In most diaphragm pump models, a material funnel can be screwed on directly for processing small quantities of paint.

As a result, the path of the paint is particularly short, and as little material as possible is required for filling and operating the paint spraying device. In the processing of small quantities of material, 1.5 l for example, a short material path is advantageous since less paint is required to fill the spraying device.

In the case of piston pumps, suction is usually carried out from below, so that funnels are usually connected to the piston pump via an additional material tube, and thus more paint is required for filling.

In addition, it is also possible to operate more powerful diaphragm pumps with short and thinner paint hoses (for example, 7.5 m in length and an internal diameter of 4 mm (DN4)).

This also reduces the material requirement for filling and operating the pump. In the case of more powerful electric piston pumps, longer hoses with a larger internal diameter are necessary, otherwise it could easily come to feedback effects which can adversely affect the spray pattern.

Diaphragm pump as a combo unit for varnish and emulsion paint

The use of Airless diaphragm pumps is also suitable for those who want to use a paint spraying unit to apply varnish and dispersion paints, since diaphragm pumps can be quickly converted and equipped with a funnel for small quantities.

As we said before, diaphragm pumps have an advantage when the processing of small quantities of less than 5 liters, and this is often the case with residential sanitation and the painting of radiators, windows and doors.

Of course, there are also suitable electric piston pumps for these application areas, but if you usually work with lacquer and emulsion paint you will be better off with a diaphragm pump.

Piston pumps for highly viscous materials such as plaster or bitumen

Both diaphragm pumps and piston pumps can be used for lacquers, glazes, emulsion, mineral or latex paints. For highly viscous materials such as fire protection, bitumen or filler, it looks very different.

Piston pump technology should be used here since these working areas require performance values ​​and capabilities beyond those of most diaphragm pumps.

 

Feature or Factor

Diaphragm

Piston

Simple
Wear and tear
Cost of repair
Small quantities
Thicker materials
Price

Graco ProConnect has made replacing pumps easy and effortless while on the job site.

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