To avoid staining fabric, the air in an upholstery workshop must pass through a refrigerated dryer, a particulate filter and a coalescing filter at the compressor outlet, then through a fine filter, or even an activated carbon filter, in front of the blow gun and the glue spray gun. The stains almost always come from condensed water, from oil carried over by a poorly filtered compressor, or from an over-lubricated tool. The K 75 4-in-1 already combines the dryer and the filtration; all that remains is to add the filters at the point of use.
The air needs of the trade are presented on our page compressor for upholstery and trimming.
Why does compressed air stain fabric?
The surrounding air contains water vapour. The compressor concentrates it, and when the compressed air cools in the air receiver and the pipes, this water condenses. Without a dryer, it travels along the network and comes out in spurts at the blow gun or the glue spray gun.
In an upholstery workshop, the consequences show straight away:
- A water ring on velvet, silk or natural leather, which marks the fabric as it dries.
- A grey stain when the water is loaded with oil and dust: it will not come out.
- Rust spots on the staples and in the magazine of the staple guns, which end up marking the fabric around the staple.
- Adhesive that does not bond properly when the spray gun sprays water along with the glue.
Where does the oil in the air come from?
Our screw compressors are lubricated: the oil cools and seals the screw element, then an air/oil separator recovers it. A very small amount is still carried along in the air. It is the filtration at the outlet that holds it back. The sources of oil on the fabric are therefore often somewhere other than the compressor itself:
- Filtration that is missing or saturated. A coalescing filter whose element has not been changed no longer stops anything.
- An air/oil separator at the end of its life, letting through more oil than the filtration can stop.
- Condensate that is never drained, which builds up at the bottom of the air receiver and goes back into the network.
- An over-oiled tool. Some staple guns need a few drops of oil at the air inlet. If you put in too much, the tool blows oil out through its exhaust, straight onto the piece.
- A lubricator on the line that also supplies the blow gun: oily air meant for a tool ends up on the fabric.
Which treatment chain for an upholstery workshop?
| Step | Role | Where |
|---|---|---|
| Refrigerated dryer | Lowers the dew point and condenses the water before the network | At the compressor outlet, after the air receiver |
| Particulate filter | Stops dust and rust | After the dryer |
| Coalescing filter | Stops oil and water aerosols | After the particulate filter |
| Automatic drain | Removes condensate from the air receiver and the dryer | Air receiver, dryer, low points |
| Fine filter at the point of use | Captures anything that has formed in the network | In front of the blow gun and the glue spray gun |
| Activated carbon filter | Captures oil vapours and odours | In front of the tool that blows onto light-coloured fabrics |
A refrigerated dryer is generally enough for a heated workshop. If the pipework runs through a courtyard or a cold room in winter, the dew point has to be lower than the coldest temperature along the route: a desiccant (adsorption) dryer may then be necessary. For a trimming shop working for a customer who requires an air quality class, our technicians will define the treatment with you under the ISO 8573-1 standard.
Sizing the dryer and filters: an example
Take a trimming workshop equipped with an S 55, a standalone screw compressor that delivers 0.6 m³/min at 8 bar, with a blow gun and a glue spray gun.
The dryer and the outlet filters are sized on the compressor's output, not on the tools: 600 l/min as a minimum. If the room goes above 30 °C in summer, take a capacity about 20% higher: 600 × 1.2 = 720 l/min. A dryer designed for a 7.5 kW compressor, such as our refrigerated dryer for a 7.5 kW compressor, gives you that margin.
The filters at the point of use are sized on the tool. The blow gun uses around 150 l/min, and the glue spray gun around 150 l/min too. With a 25% margin: 150 × 1.25 = about 190 l/min per filter. A smaller filter would restrict the air and drop the pressure at the gun.
With a K 75, the dryer and the outlet filtration are built into the frame and sized for its 1.1 m³/min. All you need to add are the fine filters at the workstations.
The white cloth test
Before looking any further, do the test: open the blow gun for a few seconds onto a clean white cloth, 20 cm away. A damp cloth points to a drying or draining problem. A yellow or grey mark points to oil. Repeat the test as close as possible to the compressor, then workstation by workstation, to locate the source. Our article on oil stains on laundry explains this method in detail.
The maintenance that stops the stains coming back
- Change the filter elements when the manufacturer says so, or earlier if the pressure drop increases.
- Check the drains every week: a blocked automatic drain fills the air receiver with water.
- Keep up the compressor's maintenance: first service at 500 hours, then every 1,500 hours, with the air/oil separator replaced when it is due.
- Separate the lines: one line with a lubricator for the tools that need it, and one dry, filtered line for the blow gun and the glue spray gun.
For a compressor with the right treatment, select the "Painting and finishing" air quality in the configurator, which provides for dry, filtered air, or ask our technicians for advice with a quote request.
For your trade: Compressor for upholstery, auto trimming and soft furnishing workshops.