With airless and air-assisted airless (often called airmix), the compressor first feeds the pump's air motor, which puts the paint under high pressure. The air flow is read from the pump curve, at the paint flow you want; with air-assisted airless you add the gun's atomising air. A pressure of 8 bar is usually enough: flow and dry air decide the model.
Airless, air-assisted airless: what uses the air?
- With airless, the paint is atomised by its own pressure through a calibrated tip. Compressed air only drives the pump motor. The gun receives no air.
- With air-assisted airless, the paint leaves at a lower pressure and a small air supply at the gun refines the pattern. There are two consumers: the pump motor and the atomising air.
- If your pump is electrically driven, only the atomising air of the air-assisted gun counts for the compressor.
Our page on compressors for spray booths covers the air supply of a booth. Here we size for pumps.
The pump's pressure ratio
An air-driven pump is defined by its pressure ratio, for example 30:1. With 6 bar of air on the motor, it gives in theory 6 × 30 = 180 bar on the paint. Fluid pressure is therefore set with the pump's air regulator.
Two consequences for the compressor:
- It must deliver at least the maximum useful air pressure for the motor, given in the manual. The 8 bar version covers most cases; check your pump's value before choosing a 10 or 13 bar version.
- More pressure costs flow. On the K 150, flow goes from 2.2 m³/min at 8 bar to 2.0 m³/min at 10 bar and 1.6 m³/min at 13 bar.
Reading consumption from the curve
A pump manual gives curves linking paint flow, fluid pressure and air consumption. The bigger the tip and the higher the pressure, the more cycles per minute the pump makes, and the more air it uses.
Take the consumption at the most demanding operating point: the largest tip you will use, at the highest pressure. If the curve is in m³/h or cfm, our flow and pressure converter turns it into L/min.
Worked example
The values below are example assumptions: replace them with those in your manuals.
- One large airless pump for primers: 600 L/min of motor air at its operating point.
- Two air-assisted pumps for topcoats: 2 × 250 L/min = 500 L/min.
- Atomising air for the two air-assisted guns: 2 × 100 L/min = 200 L/min.
- A dusting blow gun, around 150 L/min counted at 50 %: 75 L/min.
- Total: 1,375 L/min.
- With a 25 % margin: 1,375 × 1.25 = about 1,720 L/min.
This need is slightly above the 1.7 m³/min of the K 110: you move up to the K 150, which delivers 2.2 m³/min at 8 bar.
Which compressor for which workshop?
- One air-assisted pump and a touch-up station: the K 75. 1.1 m³/min at 8 bar, 420 L receiver, built-in refrigerated dryer and filtration.
- Two or three pumps: the K 110 or the K 150. 1.7 and 2.2 m³/min at 8 bar, same built-in air treatment.
- An existing network with its receiver and dryer: the S 150. Standalone screw compressor, 2.2 m³/min at 8 bar.
- A line with several booths: an industrial project. Beyond 22 kW, our screw compressors go up to 132 kW on request.
Pitfalls specific to pumps
- Motor icing. Air expands and cools at the pump exhaust. Moist air encourages ice, and the pump starts to stroke irregularly. Dry air from a dryer limits this risk.
- Atomising air. It touches the paint directly: it needs the same quality as a conventional gun, dry and filtered, with fine filters at the station. The air class is set with our technicians according to ISO 8573-1. Our compressors are lubricated: filtration is what holds back oil aerosols.
- The lubricator. On an air-assisted pump, motor air and gun air often come from the same regulator block. Do not fit a lubricator there without the pump maker's approval.
- Flow peaks. At each stroke change, the pump draws air all at once. A receiver near the booth smooths these demands; our air receiver size calculator helps you choose one.
Send us your pump curves with a quote request: we will run the calculation with you and propose the right model and receiver.
For your trade: Compressor for spray booths.