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Quotes - Engineering - SalesWhat a two-stage shop compressor asks of its dryer
Higher pressure, hotter air, a busier duty cycle than the small units
The 7.5 and 10 hp two-stage piston unit on an 80 gallon tank is the standard compressor of the auto shop, the tire store and the small fabricator. It delivers 26 to 40 SCFM at 150 to 175 psig, hot and in bursts, and the dryer behind it is either a 35 to 60 SCFM high-inlet-temperature model or a 42 to 50 SCFM standard unit behind an aftercooler.
Two-stage heads discharge at 175 psig and 180 to 200°F, and a busy shop keeps them running 40 to 60 percent of the day. The pressure works for the dryer, the temperature works against it, and the tank between them is the only thing that evens out the pulses.
7.5 hp
- 26 to 30 SCFM delivered
- Dryer 32 SCFM cooled; 35 SCFM high-inlet
- Two-bay auto shops, small body shops
10 hp
- 35 to 40 SCFM delivered
- Dryer 42 to 50 SCFM cooled; 50 to 60 SCFM high-inlet
- Tire stores, fleet garages, sign fabricators
10 hp in a 110°F shop
- 35 to 40 SCFM delivered
- Dryer 50 SCFM cooled; 60 SCFM high-inlet
- Un-ventilated compressor closets in summer
Duplex 7.5 hp, both running
- 52 to 60 SCFM delivered
- Dryer 65 SCFM cooled; 75 to 80 SCFM high-inlet
- Truck shops and dealerships with two compressors on one tank
Horsepower to dryer size, 7.5 and 10 hp
Delivered flow at 3.5 to 4 SCFM per hp. The cooled column assumes an aftercooler bringing the air to about 100°F ahead of a standard dryer; the high-inlet column is the 180 to 200°F rated dryer connected at the tank outlet.
| COMPRESSOR | DELIVERED FLOW | DRYER, AIR COOLED TO 100°F | DRYER, NO AFTERCOOLER | DRYER BAND |
| 7.5 hp | 26 to 30 SCFM | 32 SCFM | 35 SCFM high-inlet | 5 to 50 SCFM |
| 10 hp | 35 to 40 SCFM | 42 to 50 SCFM | 50 to 60 SCFM high-inlet | High inlet temperature |
| 10 hp at 150 psig | 35 to 40 SCFM | 32 to 42 SCFM (factor 1.15) | 50 SCFM high-inlet | 5 to 50 SCFM |
| 10 hp, tank plus pipe run (120°F inlet) | 35 to 40 SCFM | 55 to 65 SCFM (factor 0.65) | 50 to 60 SCFM high-inlet | 65 to 250 SCFM |
| 10 hp, 110°F shop, aftercooled | 35 to 40 SCFM | 50 SCFM (factor 0.88) | 60 SCFM high-inlet | 5 to 50 SCFM |
| Duplex 7.5 hp, both running | 52 to 60 SCFM | 65 SCFM | 75 to 80 SCFM high-inlet | 65 to 250 SCFM |
Straight off the tank: 35 to 60 SCFM high-inlet-temperature dryers
The 35, 50 and 60 SCFM sizes accept 180 to 200°F air on 115 V, with a separator and zero-loss drain built in and a 50°F pressure dew point that keeps water out of impact wrenches, lifts and tire machines. Put the 450°F particulate filter ahead 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.
Behind an aftercooler: 42 to 65 SCFM standard dryers
Where the shop paints, an aftercooler and separator ahead of a 42 to 65 SCFM standard dryer give the 38°F dew point a spray gun wants. Cycling models at 30 to 65 SCFM suit a compressor that idles between jobs.
- 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.
- 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.
Installing a dryer on an 80 gallon two-stage compressor
Two decisions set the installation: whether the shop adds an aftercooler, and how far from the tank the dryer sits.
Measure the air temperature at the tank outlet with the compressor cycling on a warm afternoon. Above 130°F the choice is a high-inlet-temperature dryer at the tank or an aftercooler; between 115 and 130°F a standard dryer one or two sizes up will cope; below 115°F size a standard dryer normally. A tank and 20 to 30 ft of iron pipe often bring 190°F air down to 120 to 130°F, which is still 20 to 30°F above the standard rating point.
Pipe the dryer after the tank with a filter ahead of it, the high-temperature grade for hot air or a 1 micron coalescer for cooled air, and a 0.01 micron oil-removal afterfilter behind. Check the dryer's pressure rating against the tank: the small dryers are rated 200 to 232 psig, which covers a 175 psig two-stage unit. Use a three-valve bypass above 35 SCFM, and give the tank a zero-loss automatic drain so its water stays out of the dryer.
A 10 hp two-stage unit connected at the tank is the 50 or 60 SCFM high-inlet-temperature dryer; with an aftercooler it is the 42 or 50 SCFM standard model.
Size a dryer for my 10 hp compressor
Running a dryer on an 80 gallon two-stage
It means the dryer spends roughly half the day with no air flowing through it. A non-cycling unit keeps its refrigeration compressor running through every one of those gaps. On the aftercooled route, a cycling model in the 30 to 65 SCFM range stops it and holds the dew point from it's thermal mass until the compressor restarts. At this size the saving is modest, so it pays best where the compressor is also left on through evenings and weekends.
No. The small dryers are rated 200 to 232 psig, which leaves margin over a 175 psig cut-out. Check the filter housings and bypass valve separately, though, since a bowl borrowed from a 125 psig shop line may not carry the same rating. The higher pressure is a help to the dryer itself, because each standard cubic foot of air brings less vapor into it at 175 psig than it would at 100 psig.
Impact wrenches, lifts, tire machines and inflation cages run happily on 50°F air in a heated building, so the high-inlet-temperature dryer at the tank is the simpler install. The picture changes if the store also runs a paint gun or does body repair in one of its bays. Then an aftercooler and a standard dryer holding 38°F become worth the extra parts and the extra floor space.
Heat costs a size on either route. An aftercooled unit in a 110°F closet takes the 0.88 factor and needs the 50 SCFM standard dryer instead of the 42; straight off the tank, the high-inlet-temperature model moves to the 60 SCFM size. A louvered door or an exhaust fan on the closet often wins back that size for a fraction of the price, and the compressor runs cooler too.
