For powder coating, a refrigerated dryer is enough in most shops: it brings the pressure dew point down to a few degrees above zero, which is fine for an air network that stays inside a heated building. A desiccant dryer becomes necessary when the air passes through a cold zone, or when your gun or powder supplier asks for a sub-zero dew point. It all comes down to comparing two temperatures.
Powder is more sensitive to water than most paints, which is why our page on the compressor for powder coating stresses drying. Here we explain how to choose the dryer.
Pressure dew point, in plain terms
The pressure dew point is the temperature at which the water held in compressed air condenses. Air with a 5 °C dew point stays dry as long as it does not cool below 5 °C. If it runs through a pipe at 2 °C, liquid water forms in that pipe and then travels to the hopper.
In powder coating, that water causes lumps, upsets fluidising, disturbs the electrostatic charge and blocks injectors. The defects often only show up when parts leave the oven, too late to save them.
The method in three steps
1. Find the coldest point on the air's route. Follow the network from the compressor to the booth: runs along an outside wall, under a canopy, through a loading bay or an unheated room, or a booth at the far end of a hall that gets cold at night. Note the lowest temperature of the year at that spot.
2. Compare it with the dryer's dew point. A refrigerated dryer cannot go below 0 °C, or water would freeze in its heat exchanger. On our L series, for example, the built-in refrigerated dryer is rated for a dew point of 3 to 10 °C. Keep a few degrees of margin: the dew point must stay well below the coldest temperature in the network.
3. Check what your suppliers require. Some gun or powder unit manufacturers specify an air class under ISO 8573-1, with a set dew point. If the class calls for a sub-zero dew point, only a desiccant dryer will reach it.
Two worked examples
Heated shop. The network never leaves the shop, which stays above 15 °C even on winter nights. With a dew point of 3 to 10 °C, the margin is enough: a refrigerated dryer will do.
Network running outside. The same air line follows 20 m of outside wall, where the pipe drops to 2 °C in winter. A refrigerated dryer's dew point sits above that temperature, so water will condense in that section. Two fixes: reroute the pipe indoors, or fit a desiccant dryer.
Which compressor with which dryer?
- Built-in refrigerated dryer. The 4-in-1 compressors of the K series combine the screw unit, receiver, refrigerated dryer and filtration. The K 150 delivers 2.2 m³/min at 8 bar and can supply several manual booths or a small line.
- Separate refrigerated dryer. With a standalone compressor from the S series, you add a refrigerated dryer sized for its power, plus a receiver and filters.
- Desiccant dryer. It goes after a standalone compressor, with a fine pre-filter upstream (oil damages the desiccant) and a dust filter downstream.
Watch the flow with a desiccant dryer: regenerating the desiccant uses part of the compressed air. On heatless models, that share is often around 15 to 20%, to be checked on the dryer's data sheet. Example for an installation using 1,500 l/min:
- Equipment demand: 1,500 l/min
- Regeneration air, 18% assumed here: 1,500 × 0.18 = 270 l/min
- Total demand: 1,770 l/min
- Choice: the S 110 (1.7 m³/min at 8 bar) is too tight, the S 150 (2.2 m³/min at 8 bar) fits.
Mistakes to avoid
- An undersized dryer. A dryer treats less air when the room is hot or the incoming air is warm. Build in a margin. See which air dryer to choose.
- Forgotten drains. The dryer removes vapour; drains remove liquid water from the receiver, dryer and filters. An automatic condensate drain that has stopped working sends water back into the network. See water in compressed air.
- Oil. Our screw compressors are oil-lubricated. A dryer does not replace fine filters, which hold back the oil aerosols that cause craters after curing.
To choose the compressor and its air treatment, start with the configurator, then describe your network's route in a quote request: our technicians will define the air class and the dryer with you.
For your trade: Compressor for powder coating.