1-805-484-2992
Quotes - Engineering - SalesWhat an industrial piston compressor asks of its dryer
Real plant flows with a piston's pulses and, sometimes, a piston's temperature
At 15 hp and above the reciprocating compressor is competing with a screw for the same job, and the dryer sizing follows the screw rules once an aftercooler is in place: flow from the data sheet, inlet 15 to 20°F above room, correction for a hot compressor room. Without the aftercooler the flow is high enough that only the largest high-inlet-temperature sizes will carry it.
15 hp
- 52 to 60 SCFM delivered
- Dryer 65 SCFM cooled; 75 to 80 SCFM high-inlet
- Body shops, truck fleets, small plants
20 hp
- 70 to 80 SCFM delivered
- Dryer 85 SCFM cooled; 80 to 100 SCFM high-inlet
- Woodworking shops, blast rooms
25 hp
- 88 to 100 SCFM delivered
- Dryer 105 SCFM cooled; 100 to 125 SCFM high-inlet
- Dealership service floors, sawmills
30 hp
- 105 to 120 SCFM delivered
- Dryer 125 SCFM cooled; 125 SCFM high-inlet at the limit
- Duplex 15 hp units on one tank land here too
Horsepower to dryer size, 15 to 30 hp
Delivered flow at 3.5 to 4 SCFM per hp. The cooled column assumes an aftercooler ahead of a standard dryer at the rating point; the high-inlet column is the 180 or 200°F rated dryer on the tank outlet, which tops out at 100 to 125 SCFM.
| COMPRESSOR | DELIVERED FLOW | DRYER, AFTERCOOLED (100°F) | DRYER, NO AFTERCOOLER | DRYER BAND |
| 15 hp | 52 to 60 SCFM | 65 SCFM | 75 to 80 SCFM high-inlet | 65 to 250 SCFM |
| 20 hp | 70 to 80 SCFM | 85 to 90 SCFM | 80 to 100 SCFM high-inlet | 20 to 250 SCFM cycling |
| 25 hp | 88 to 100 SCFM | 105 to 110 SCFM | 100 to 125 SCFM high-inlet | 65 to 250 SCFM |
| 30 hp | 105 to 120 SCFM | 125 to 130 SCFM | 125 SCFM high-inlet, or add an aftercooler | High inlet temperature |
| 30 hp, aftercooled, 110°F room | 105 to 120 SCFM | 150 SCFM (factor 0.88) | Aftercooler required | 20 to 250 SCFM cycling |
| Duplex 15 hp, both running | 105 to 120 SCFM | 125 to 130 SCFM | 125 SCFM high-inlet | 65 to 250 SCFM |
Aftercooled: the 65 to 150 SCFM standard dryers
With an aftercooler on the compressor the dryer is sized like any other 65 to 130 SCFM duty: the non-cycling line steps through 65, 85, 105, 125 and 150 SCFM and the cycling lines run 65 to 170 SCFM in similar increments, all on 115 V. The previous-generation plant dryers in this range cross-reference to the current models.
- 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.
- HPRN Series: Non-cycling refrigerated dryer from 75 to 1,200 SCFM for plant air on a single compressor; previous generation, cross-referenced to current models.
- TMC Series: Thermal-mass cycling dryer from 30 to 635 SCFM; stores cold in a thermal mass so the refrigeration compressor rests when air demand drops.
- NXC Series: Cycling dryer in 19 sizes from 20 to 2,000 SCFM with a dry thermal mass and up to 80 percent power savings at part load.
- FLXA Series: Current cycling dryer, 75 to 2,000 SCFM, air- or water-cooled, with low-GWP refrigerants and a heat-transfer cycling control that follows the load.
Hot air: the top of the high-inlet-temperature range
The 75, 80, 100 and 125 SCFM high-inlet-temperature dryers carry a 15 to 25 hp piston without an aftercooler; at 30 hp the 125 SCFM size is at its limit and an aftercooler becomes the better investment. A 450°F filter goes ahead of all of them.
- 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.
Installing a dryer behind a 15 to 30 hp piston unit
Pulsation, condensate volume and the duplex question shape the installation more than the flow number does.
A 25 hp piston moving 100 SCFM in pulses needs a receiver ahead of the dryer sized to smooth them, normally 120 to 240 gallons, and that receiver collects several gallons of water a day in summer. Give it a zero-loss drain and a separator at the aftercooler outlet so the dryer's own separator only handles the fine mist. Connections move to 1 in NPT at 85 to 150 SCFM; keep the filter housings the same size as the dryer.
A duplex unit with two 15 hp heads on one tank is sized for both running together, 105 to 120 SCFM, because the controller will start the second head whenever the shop demand climbs. One dryer after the common tank, with a three-valve bypass and a 1 micron prefilter ahead and a 0.01 micron afterfilter behind, serves both heads and costs less than two 65 SCFM dryers.
A 20 hp aftercooled piston is the 85 or 90 SCFM dryer; the same unit without an aftercooler needs the 100 SCFM high-inlet-temperature model, and the 30 hp version needs an aftercooler either way.
Size a dryer for my duplex compressor
15 to 30 hp piston compressor dryer questions
A 20 hp piston delivers 70 to 80 SCFM. With an aftercooler the 85 or 90 SCFM standard dryer is the match; straight off the tank it needs the 80 or 100 SCFM high-inlet-temperature model, and the 100 leaves margin for a hot summer.
The 65 to 250 SCFM band. Both heads together deliver 105 to 120 SCFM at about 100°F, so the 125 or 130 SCFM dryer covers it in a normal room and the 150 SCFM size in a compressor room that runs 110°F.
At 105 to 120 SCFM the 125 SCFM high-inlet-temperature dryer will carry it, but with no margin for a hot room. The better answer at 30 hp is an air-cooled aftercooler and separator, which costs less than the next dryer size and opens up the whole 65 to 250 SCFM band at a 38°F dew point.
No. Both heads discharge into one tank, so one dryer after the tank sized for the combined flow is simpler, cheaper and easier to bypass than a dryer per head. Two dryers only make sense where the heads are on separate tanks feeding separate systems.
A piston compressor that starts and stops is already telling you the load is intermittent, and a cycling dryer rests along with it. At 100 to 130 SCFM the cycling models draw about 1 kW and spend most of a one-shift day stopped, which repays the premium over a non-cycling unit within a few years.
