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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
Piston compressors from 15 to 30 hp are industrial machines: pressure-lubricated, often duplexed on one tank, and usually fitted with an aftercooler. They deliver 52 to 120 SCFM, which takes the dryer into the 65 to 250 SCFM band, while the units that still discharge hot air sit at the top of the high-inlet-temperature range.
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
Tank, pulsation and piping at 15 to 30 hp
Several gallons a day on a humid summer shift, most of it dropping out in the receiver and the aftercooler separator rather than the dryer. That volume is why the tank needs a zero-loss drain sized for it; a manual petcock opened once a week lets the tank fill and pushes water downstream in slugs. Route every drain to an oil-water separator, since these compressors are pressure-lubricated.
The receiver protects it, provided it is large enough. A 25 hp piston moving 100 SCFM in pulses wants 120 to 240 gallons ahead of the dryer; on a smaller tank the flow through the dryer swings with every stroke and the separator carries water it should have dropped. Standing the dryer on the floor beside the tank, not on the compressor frame, keeps vibration out of its refrigeration piping.
Size the piping to the dryer's connections rather than to the compressor's outlet. From 85 to 150 SCFM the dryers connect at 1 in NPT, and the prefilter and afterfilter housings should match that size; a smaller filter housing becomes the restriction that makes the compressor run to a higher cut-out pressure. Keep the run from the receiver to the dryer short and free of reducers.
