A powder coating booth with 2 manual guns typically needs around 400 to 650 l/min of compressed air, booth and blow gun included. A 7.5 kW 4-in-1 screw compressor such as the K 75, which delivers 1,100 l/min at 8 bar with a built-in dryer and filtration, covers that demand with capacity to spare.
This article looks at the small manual booth. For the wider picture (automatic lines, air quality, servicing), see our page on the compressor for powder coating.
What uses air in the booth?
An electrostatic powder gun does not draw air from a single point. It uses air for:
- powder conveying through the injector, from the hopper or box to the nozzle;
- dosing air, which sets the density of the powder cloud;
- electrode rinsing, which stops powder building up on it;
- fluidising the hopper, or vibrating and fluidising the box feed.
All in, allow roughly 80 to 150 l/min per gun. On top of that come the cartridge cleaning pulses of the booth filters and the blow gun used to prepare parts and clean the gun at colour change. These figures are indicative only: your equipment manuals take precedence.
The calculation, step by step
The first question is simple: do both guns spray at the same time? Two operators coating together, or one gun in use while the other waits for the next colour. The answer can double the result.
Case A, both guns at once:
- Guns: 2 × 130 l/min = 260 l/min
- Cartridge cleaning on a small booth, average: 120 l/min
- Blow gun: 200 l/min × 30% use = 60 l/min
- Total: 440 l/min
- 25% margin for leaks and wear: 440 × 1.25 = 550 l/min
Case B, one gun at a time:
- Gun: 130 l/min
- Cartridge cleaning: 120 l/min
- Blow gun: 60 l/min
- Total: 310 l/min, or about 390 l/min with the margin
On pressure, powder coating control units usually need a supply of around 6 bar: check the exact value in the manual. A compressor set to 8 bar keeps a margin for losses across the dryer, filters and hoses. The flow and pressure converter switches between l/min, m³/min and cfm if your data sheets use another unit.
Which model for your booth?
| Situation | Recommended model |
|---|---|
| New booth, no dryer or receiver yet | K 75, 1.1 m³/min at 8 bar, 420 L receiver, built-in refrigerated dryer and filtration |
| Dryer, receiver and filters already in place | S 75, 1.1 m³/min at 8 bar, standalone compressor |
| Case B only, tight budget, existing air treatment | S 55, 0.6 m³/min at 8 bar |
| Second booth or larger oven planned | K 110, 1.7 m³/min at 8 bar, 4-in-1 |
A word on the S 55. Its 600 l/min covers case B comfortably, but case A only just: the day a third station arrives, it runs short. The K 75 remains the safer choice for a two-gun booth, with room for one more gun. Note that it connects to a 400 V three-phase supply: check your installation before ordering.
What about a piston compressor? The guns blow non-stop for the whole coating session. A piston compressor is built for intermittent use, and it runs hot and wears quickly under that duty. A screw compressor handles continuous work. The difference is explained in piston or screw compressor.
Traps specific to a manual booth
- Colour change. You blow out the gun, hose and hopper, often with several blow guns at once. That is the peak demand of the day. The K 75's 420 L receiver absorbs it without the pressure dropping at the guns.
- Moisture. Damp air makes lumps in the hopper and spitting at the nozzle. If the compressor has no built-in dryer, add one. See which air dryer to choose.
- Oil. Our screw compressors are oil-lubricated, so the air leaving them carries traces of oil. On a coated part, they show up as craters after curing. Fine filters in series, just ahead of the powder unit, hold them back. See fine filters for compressed air. The ISO 8573-1 air class to aim for is set with our technicians.
- A hose that is too narrow. A long, small-bore hose between compressor and booth loses pressure at high flow. The guide to connecting a compressor to the air network sets out good practice.
- A compressor in the powder. Fine airborne powder clogs the intake filter fast. Install the compressor outside the coating area, in a ventilated room: see the compressor room.
So for two guns spraying together, start from about 550 l/min, held at 8 bar with dry, filtered air. The configurator checks your case in a few clicks. Then send us your gun and booth manuals with a quote request: we will confirm the flow with you.
For your trade: Compressor for powder coating.