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Quotes - Engineering - SalesWhat a small piston compressor asks of its dryer
Hot pulses of air, short run cycles, one user at a time
At this size the compressor runs for a few minutes to fill the tank and stops, so the dryer sees full compressor output, hot, then nothing. The flow is small enough that one dryer model covers the whole class; the inlet temperature is what decides which model it is.
2 hp
- 7 to 8 SCFM delivered
- Dryer size 7 to 11 SCFM cooled; 25 SCFM high-inlet
- Home shops, tire inflation, one nail gun
3 hp
- 10 to 12 SCFM delivered
- Dryer size 11 to 15 SCFM cooled; 25 SCFM high-inlet
- Trim carpentry, small paint guns, farm shops
5 hp
- 17 to 20 SCFM delivered
- Dryer size 20 to 25 SCFM cooled; 25 SCFM high-inlet
- One-bay garages, sandblast cabinets, dental labs
5 hp two-stage, 150 psig
- 17 to 18 SCFM delivered
- Dryer size 20 SCFM; pressure factor 1.15 helps
- Impact wrenches and lifts on a 175 psig tank
Horsepower to dryer size, 2 to 5 hp
Delivered flow at 3.5 to 4 SCFM per hp. The cooled column assumes an aftercooler or a receiver and long pipe run bringing the air to 100°F; the high-inlet column is the dryer rated for 180 to 200°F air connected at the tank outlet.
| COMPRESSOR | DELIVERED FLOW | DRYER, AIR COOLED TO 100°F | DRYER, NO AFTERCOOLER | DRYER BAND |
| 2 hp | 7 to 8 SCFM | 7 to 11 SCFM | 25 SCFM high-inlet | 5 to 50 SCFM |
| 3 hp | 10 to 12 SCFM | 11 to 15 SCFM | 25 SCFM high-inlet | 5 to 50 SCFM |
| 5 hp | 17 to 20 SCFM | 20 to 25 SCFM | 25 SCFM high-inlet | High inlet temperature |
| 5 hp, 150 psig two-stage | 17 to 18 SCFM | 20 SCFM (factor 1.15) | 25 SCFM high-inlet | 5 to 50 SCFM |
| 5 hp, tank plus 20 ft of pipe (120°F inlet) | 17 to 20 SCFM | 32 SCFM (factor 0.65) | 25 SCFM high-inlet | 5 to 50 SCFM |
| Two 5 hp on one tank, both running | 35 to 40 SCFM | 42 to 50 SCFM | 50 to 60 SCFM high-inlet | High inlet temperature |
No aftercooler: dryers rated for 180 to 200°F air
The 25 SCFM high-inlet-temperature dryers cover every single compressor in this class straight off the tank, on 115 V, with a separator and zero-loss drain built in. A 450°F particulate filter ahead of the dryer catches the carbon and oil a hot piston head sheds.
- HRHT Series: Current high-inlet-temperature dryer, 25 to 100 SCFM, rated for 200°F inlet air from reciprocating compressors with no aftercooler.
- HTR Series: High-temperature direct-expansion dryer, 25 to 125 SCFM, for 180°F inlet air from piston compressors on shop and service-bay duty.
- GHTN High-Temperature Filters: High-temperature filter rated 450°F for air straight off a piston compressor, 15 to 1,600 SCFM.
Air already cooled: the smallest plug-in dryers
Behind an aftercooler, or where the tank and 30 ft of pipe bring the air near 100°F, the 7 to 25 SCFM non-cycling units deliver a 38°F dew point for a paint gun or a lab bench. They draw 0.15 to 0.3 kW and connect at 3/8 or 1/2 in NPT.
- HPRB Series: Current small non-cycling dryer, 7 to 50 SCFM, with low-GWP R513A refrigerant, a 3-in-1 heat exchanger and a built-in separator on the larger sizes.
- DXR Series: Direct-expansion non-cycling dryer in 27 sizes from 10 to 4,200 SCFM; the widest single range on the site, with a full data sheet behind every model.
Installing a dryer on a small piston compressor
The tank is the first stage of drying, so the dryer goes after it, and the tank drain decides whether the dryer ever gets a fair chance.
Air leaves a 5 hp head at 190°F carrying every grain of water it took in, and most of it drops out as the air cools in the tank. A tank drained once a week fills with water, the compressor pushes it downstream and the dryer's separator meets slugs of liquid it was never sized for. Fit an automatic drain on the tank first; a zero-loss float or electronic drain wastes none of a small compressor's output.
From the tank outlet run a high-temperature filter into a high-inlet-temperature dryer, or a 1 micron prefilter into a standard dryer if the air has cooled, then a 0.01 micron afterfilter where a paint gun or instrument follows. The single-body bypass valve covers dryers to 35 SCFM. Mount the dryer on the wall, not on the vibrating tank, with room behind it for condenser air.
A 5 hp compressor hosed straight to its dryer needs the 25 SCFM high-inlet-temperature unit; the same compressor with an aftercooler and 30 ft of pipe is a 20 to 25 SCFM standard dryer.
Match a dryer to my shop compressor
2 to 5 hp piston compressor dryer questions
If anything downstream minds water, yes. A 5 hp compressor in a humid shop takes in around a gallon of water a day, the tank catches most of it, and the rest arrives at the paint gun, the blast cabinet or the tire machine as mist and droplets.
The 25 SCFM high-inlet-temperature dryer, which is rated for 200°F inlet air and is the smallest size in that line. At 10 to 12 SCFM it runs well inside its rating and delivers a 50°F pressure dew point on 115 V.
Only with enough pipe between the tank and the dryer to bring the air under about 115°F, which usually means 30 ft or more of metal pipe. Connected with a short hose it sees 150°F air or hotter, cannot reach its dew point and runs its refrigeration circuit at the high-pressure limit.
A standard 7 to 25 SCFM dryer gives a 38°F pressure dew point at rated conditions, ISO 8573-1 class 4; the high-inlet-temperature units give 50°F, class 6. Both keep liquid water out of the lines in a heated shop; neither will do for lines that run outdoors in winter.
After. The tank cools the air, drops most of the water and evens out the compressor's pulses, all of which make the dryer's job easier. A dryer piped ahead of the tank sees hot pulsing air and, at this size, would need to be far larger than the compressor deserves.
