Airless Sprayer Pumps

There are several airless pump types, however the two most common are Piston and Diaphragm. We have outlined the process of fluid flow for a piston style pump below, as it is more common, but for a complete list of the advantages and disadvantages, see our piston vs. diaphragm chart below.

Some of these design names are:

  • Diaphragm
  • Single Stroke Piston
  • Double Stroke Piston

Often called the heart of an airless paint sprayer, the pump or fluid section is the component which makes airless painting possible.

Pump / Fluid Section

The pump, also called the fluid section. It is what moves and pressurizes the material to be sprayed most commonly, latex paint. Airless pumps are normally made of hardened, heavy-duty steel so they can create the high pressure needed to atomize paints and other "sprayable" materials. Some fluid sections such as Graco's Endurance Pumps have additional features like their Chromex Rod for longer wear. Current Graco Endurance Pumps also come equipped with V-Max packings for longer life. - Read more about pumps.

Cylinder

The cylinder is the part that houses the rod, packings, and balls inside a fluid section. The cylinder is also the section of the fluid pump that allows paint to flow freely throughout the pump.

Rod

The displacement rod connects the pump's internal components to the drive system. The rod moves up and down with the action of the drive system and motor. Fluid is loaded on the upstroke and displaced on both the upstroke and down stroke.

Packings

Piston packings create a seal inside the cylinder as the rod moves up and down (like a doctors syringe).

  • On the upstroke fluid is drawn into the pump because a vacuum is created as the rod goes up. As the rod goes up, fluid is pushed out to the hose. The lower ball lifts and allows fluid to be drawn into the pump, filling the cylinder. The upper ball seals the opening to the lower section.

  • On the down stroke the lower ball seals, the upper ball opens and the rod moving down displaces (the volume of the rod takes up space) fluid and forces fluid out to the hose.

Inlet

In a piston pump, the inlet is one of two ball checks that control the flow of fluid through the fluid section. When the rod is pulled up, the inlet allows paint to flow upwards from the inlet tube.

Outlet

The outlet, like the inlet valve and ball, allows paint to flow freely throughout the fluid section. When the rod is pushed down, the outlet valve directs the flow of paint outwards to the hose and gun.

Cut-away view of double-stroke piston-pump for Graco airless paint sprayers
Cut-away view of double-stroke piston-pump for Graco airless paint sprayers

Upstroke of a Piston Pump Fluid Section
Upstroke Upstroke of a Piston Pump
Downstroke of a Piston Pump Fluid section
Downstroke of a Piston Pump

There has been a recent debate about the types of paint sprayer pumps on the market, especially since this is the most important component of a sprayer. Contractors often refer to the entire unit as "the pump". There are two general types of pumps offered for airless sprayers: diaphragm and piston. The following section describes the advantages and disadvantages of each type of pump for airless applications. All Graco airless sprayer use piston style pumps.

Piston Pumps vs. Diaphragm

Advantages Disadvantages
Diaphragm Pump
  • Tight pressure control when spraying at both low and high pressures
  • High free-flow rates - good for a high volume transfer of fluids for texture applications and water
  • Usually cheaper at initial purchase
  • Pump runs continuously
  • Higher maintenance costs
  • Difficult to prime
  • Easily allows air into the paint flow - can create an erratic flow and spitting
  • Poor performance with higher viscosity fluids
  • All moving parts will need to be kept clean and requires constant maintenance
  • Hydraulic fluid may leak into the paint
Piston Pump
  • Pumps higher viscosity coatings with ease
  • Is able to produce higher pressures at common tip sizes
  • Better atomization of paint - results in less spitting
  • Ability to use longer hoses
  • Able to withstand harder uses on the job - great for professional contractors
  • Easy to repair
  • Easy to prime - faster start-up
  • Runs only when needed - does not run constantly
  • Usually results in a higher initial purchase price - however cheaper to maintain
  • Some pressure fluctuations when spraying at lower pressures (Graco's SmartControl will help to reduce this problem)

*According to Graco, 85% of professional painting contractors prefer piston pumps.