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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
A 2 to 5 hp piston compressor delivers 7 to 20 SCFM in bursts, at 180 to 200°F off the head, into a 20 to 80 gallon tank. The dryer either takes that hot air directly, which is what the 25 SCFM high-inlet-temperature unit is for, or it sits far enough downstream that the air has cooled and a 7 to 25 SCFM plug-in dryer will do.
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
Small piston compressors and their dryers
Only if something on the line minds water. A 2 hp unit making 7 to 8 SCFM for a nail gun or tire inflation can often live with a tank drain and a water separator. Once it feeds a spray gun, a sandblast cabinet or air tools that rust, the 25 SCFM high-inlet-temperature dryer at the tank outlet is the simple fix, and it plugs into an ordinary 115 V outlet.
Yes, if it is sized for both running at once. Two 5 hp heads together make 35 to 40 SCFM, which is past the single-compressor sizes in this class: the 42 to 50 SCFM standard dryer behind an aftercooler, or a 50 to 60 SCFM high-inlet-temperature unit straight off the tank. One dryer after the shared tank costs less than two and needs only one bypass.
The tank fills with water, its usable volume shrinks, and the compressor starts pushing liquid out of the tank outlet. The dryer's separator is built for mist, not slugs, so the excess carries through to the tools and the dryer looks broken when it is not. An automatic zero-loss drain on the tank is the first purchase, ahead of the dryer itself, because no dryer size cures a flooded tank.
A small piston compressor shakes its tank every time it runs, and over the years that vibration fatigues the dryer's refrigeration tubing and fittings. A wall bracket a short pipe run away isolates the dryer and also gets its condenser out of the compressor's own hot air. Leave enough space behind the dryer for its condenser fan to pull cool room air through the fins.
Usually not. Most 3 and 5 hp piston compressors run on 230 V, and the small dryers here are 115 V units, so they want their own receptacle. Even where both are 115 V, a compressor motor starting under load pulls a heavy inrush that can trip a shared breaker and take the dryer down with it. A seperate circuit keeps the dryer running while the compressor cycles.
Because the garage is the dryer's ambient and the compressor's inlet at once. Hot room air carries more water, the compressor discharges hotter, and the condenser has less temperature difference to reject heat into. A dryer sized close to the compressor's flow on a cool day runs out of capacity in a 100°F garage. Ventilate the corner the compressor sits in, or take the next dryer size up.
