To avoid marking the seats, the carpets and the headlining, the air coming out of a tornado-type cleaning gun or a blow gun must be dry and free of oil aerosols. Three elements are needed: a refrigerated dryer at the compressor outlet (pressure dew point around +3 °C), automatic condensate draining, and fine filters at the bay, with a coalescing filter and an activated carbon filter. A 4-in-1 compressor such as the K 75 already includes the dryer and the filtration; all that remains is to add the filters at the point of use.
The other sides of the trade, air flow and choosing the compressor, are covered on our page compressor for car detailing.
Where do the marks left by compressed air come from?
A compressor draws in the surrounding air with its moisture. By compressing it to 8 bar, it concentrates that water vapour into a volume eight times smaller. As long as the air is warm, the water stays as vapour. As soon as it cools, in the air receiver, the pipes or the hose, it condenses into droplets. A wash area, damp by nature, makes things worse.
Water is not alone. Our compressors are lubricated: the oil cools and seals the screw element, and a separator holds back almost all of it. A small amount gets through as aerosols and vapour, which the filtration has to stop. On top of that come particles: rust from the air receiver, dust drawn in with the air.
On fabric, the result shows quickly:
- tide marks on cloth seats and light-coloured headlinings, when a drop of dirty water dries;
- greasy stains and dull patches on suedette (synthetic suede), caused by oil aerosols;
- a greasy film on the glass and the windscreen after the blow gun has been used;
- a smell of oil or mustiness inside the car.
Our article on oil in compressed air explains the causes on the compressor side.
The treatment chain to install
| Step | Component | What it removes |
|---|---|---|
| 1 | Refrigerated dryer at the compressor outlet | water vapour, down to a pressure dew point of around +3 °C |
| 2 | Automatic drain on the air receiver and at the low points | condensed water lying in the system |
| 3 | Particulate filter at the bay | rust and dust |
| 4 | Coalescing filter at the bay | oil aerosols and remaining droplets |
| 5 | Activated carbon filter at the bay | oil vapours and odours |
The order matters: the activated carbon filter always goes after the coalescing filter, otherwise it becomes saturated with oil within a few days.
The dryer
The refrigerated dryer cools the air to condense out the water, then warms it up again before sending it to the network. As long as the studio stays above +3 °C, the air no longer condenses in the pipes. On the K 75, it is built into the frame. With a standalone compressor such as the S 55, add an air dryer sized for the compressor's output. If a pipe runs outdoors or through an unheated room, read our article which air dryer to choose: below freezing, you need a lower dew point.
Draining
The dryer and the air receiver collect the water; it still has to be removed. An automatic condensate drain gets rid of it with no one having to step in. The condensate contains oil: it has to be collected and treated, and must not go down the drain with the wash water. See water in compressed air.
The filters at the point of use
This is the step most often forgotten and the most useful one in detailing. Even with a dryer, the air can pick up impurities again in an old steel network or a dirty hose. Fit the fine filters on the drop to each interior bay, just before the hose reel, with a regulator and a pressure gauge. Our article on fine filters at the compressor outlet explains the role of each one.
What air quality class should you aim for?
The ISO 8573-1 standard classifies compressed air on three criteria: particles, water and oil. For air blown onto upholstery and interior surfaces, the usual aim is dry air with very little oil. The exact class is set with our technicians, according to your network and your requirements. Our ISO 8573-1 air quality guide explains how to read these classes, and the guide to dew point sets out the difference between pressure dew point and atmospheric dew point.
Do filters reduce the air flow?
Yes, a little, and a lot when they are saturated. A new, correctly sized filter costs around a few tenths of a bar. A clogged filter can drop the pressure by a bar or more: the tornado-type gun slows down and the cleaner comes out in large drops. Do the calculation with a margin:
- tornado-type gun: 350 l/min at 6.3 bar at the tool;
- indicative losses: dryer 0.2 bar, filters at the bay 0.3 bar, hose and couplings 0.5 bar, so 1 bar in total;
- pressure to set at the compressor: 6.3 + 1 = 7.3 bar, rounded up to 8 bar.
Choose filters whose rated flow is higher than that of the tools they supply: for a bay with a tornado-type gun and a blow gun, at least 350 × 1.25 = 440 l/min. Replace the elements when the manufacturer says so, or as soon as the clogging indicator shows it.
A simple test to check your air
Hold a clean, dry white microfibre cloth 20 cm from the nozzle and blow for thirty seconds. If the cloth stays white and dry, the air is clean. A damp ring means water: check the dryer and the drains. A grey or greasy mark means oil or particles: check the filters and the compressor's air/oil separator. Do this test every week on every interior bay, and after every service.
The maintenance that keeps the air clean
- Compressor: on our screw models, the first service is at 500 hours, then every 1,500 hours. The air/oil separator is part of the service kits.
- Dryer: condenser kept free of dust, drain checked.
- Filters: elements replaced on schedule, activated carbon included, even if it does not look dirty.
For a check of your network, enter your tools in the configurator and select an air quality for painting, or describe your installation in a quote request.
For your trade: Compressor for car detailing and valeting.