Choosing The Correct Spray Painting System Part 6 - Airless Sprayers: Piston or Diaphragm Pump?

Choosing The Correct Spray Painting System Part 6 - Airless Sprayers: Piston or Diaphragm Pump?

Posted by Matt Piggin & Nikki Michaels on 26th Sep 2019

Choosing The Correct Spray Painting System

Airless Spray Painting Systems: Should You Choose a Piston or Diaphragm Pump?

In our last article, we talked at length about airless spray painting systems. Unlike pressure-fed and HVLP systems, airless spray guns use a motor as their power source and either a diaphragm or a piston pump to push paint through the hose and onto your surface.

But what’s the difference between diaphragm and piston pumps, and how do you know which to use for which job? In this post, we’ll cover the basics of each pump, including their advantages, disadvantages, and common uses. Keep reading to learn more.

Piston pumps

           

By far the most common type of pump used in airless spray painting systems, piston pumps utilise the power of a single piston to generate high pressure that propels and atomises whatever liquid you’re spraying. In a piston pump airless system, the piston moves upward — creating a vacuum and drawing liquid into the chamber — and then falls forcefully downward, shooting liquid through the hose and out your gun tip.

Both piston and diaphragm pumps have inlet and outlet valves, but piston pumps are capable of producing much higher pressure (up to six bar) than their counterparts.

Piston pump advantages

As we just mentioned, piston pumps produce higher pressure than diaphragms, which in turn makes them capable of spraying material over further distances.

The higher pressure also lends itself to applications of high-viscosity coatings and better paint atomisation, meaning there’s less risk of paint spitting.

Piston pumps are also easier to repair, and unlike diaphragms, they run only when they’re needed rather than running constantly.

Piston pump disadvantages

While piston pumps have the edge on diaphragms when it comes to pressure, they lose out in terms of how much volume they can supply. They’re also prone to spray fluctuations when you’re using them at lower pressures (this is because a piston pump builds to max pressure; pulling the trigger results in a short ‘kickback’ of paint at a slightly higher pressure than the desired spraying pressure).

Common uses of piston pumps

If you’re applying a highly viscous material, the higher pressure of a piston pump is an absolute necessity. Piston pumps are also ideal if your job requires spraying over a long distance (tasks such as painting roofs, new homes, factory walls, or fences, like we talked about in our airless sprayers post). 

Diaphragm pumps

In a diaphragm pump, a rod powered by a motor operates diaphragms that expand and contract, taking in fluid through the inlet valve and expelling it out of the gun. These types of airless spray painting pumps provide less pressure than piston pumps (a maximum of four bar), but they offer other capabilities that pistons don’t.

Diaphragm pump advantages

Diaphragm pumps are hardier, meaning they tend to function for longer periods of time without needing repairs or replacement parts (although you do have to make sure you keep each part of a diaphragm pump clean).

They can deliver much lower fluid volumes, making them ideal for smaller jobs (particularly ones where product is at a premium, as you can use both a shorter and thinner hose than you can with a piston pump) — and although piston pumps offer better moveability, the compact nature of diaphragm pumps means they win when it comes to portability.

Diaphragm pumps also offer better pressure control across the full pressure spectrum and don’t have the initial kickback associated with piston pumps.

Diaphragm pump disadvantages

If you need very high pressure, steer clear of the diaphragm pump; they offer lower pressure than pistons, which consequently makes them a no-go if you need to work with high solids coatings. This lower pressure also means diaphragm pumps aren’t great at spraying across longer distances.

The build of a typical diaphragm pump can sometimes let air penetrate the paint flow, increasing the risk of inconsistent pumping and spitting.

Common uses of diaphragm pumps

Diaphragm pumps are great for any application with standard-viscosity paints, and they’re commonly used for decorative applications, painting new homes, repaints, and finishing lines (because there’s no fluctuation in pressure like there can be with piston pumps).

A quick recap

Piston pumps offer higher pressure, better paint atomisation, and superior range of material handling. If you’re working with high-viscosity liquids, always choose a piston.

Diaphragm pumps offer higher volume, better portability, and better pressure control, but they work at lower overall pressure. If you need to spray smaller quantities of material or if you’re spraying large volumes over shorter distances, choose a diaphragm.

Still not sure which is right for you? I’m happy to help; just get in touch!