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Quotes - Engineering - SalesWhat a paint booth asks of its dryer
Flow from the guns, quality from the filters, no hardware inside the booth
A paint booth is the point-of-use load with the least tolerance for water and oil: a droplet is a fisheye, a trace of compressor oil is a crater, and both show up after the clear coat. The duty is 30 to 100 SCFM from guns, sanders and supplied-air hoods, and the answer is a refrigerated dryer holding 38°F followed by 0.01 micron coalescing and activated carbon.
A spray gun draws 10 to 15 SCFM while the trigger is pulled, a dual-action sander about the same, a supplied-air hood 6 to 15 SCFM continuously, and a booth with two painters and their prep station reaches 60 to 80 SCFM at its peak. The dryer delivers dry air; the two filters behind it deliver clean air; and all of it lives outside the booth's classified area.
One gun, one painter
- 10 to 15 SCFM at the gun, 30 to 45 psig inlet
- Dryer size 20 to 25 SCFM
- Small body shops, cabinet finishing
Two guns plus sanders
- 30 to 40 SCFM peak
- Dryer size 42 to 50 SCFM
- Collision shops with a prep station
Two painters with supplied-air hoods
- 40 to 60 SCFM peak
- Dryer size 65 SCFM
- Hoods take their own breathing-air filter after the dryer
Production booth, four guns
- 80 to 100 SCFM peak
- Dryer size 105 to 125 SCFM
- Truck, trailer and industrial finishing lines
Booth duty to dryer size
Peak draw from the guns and hoods that can spray at once. Dryer sizes at plant-temperature inlet and 100 psig; the second column applies the 0.88 factor for a compressor room or paint mix room that reaches 110°F in summer.
| BOOTH DUTY | PEAK AIR DRAW | DRYER SIZE AT 100°F | DRYER SIZE, HOT ROOM (110°F) | DRYER BAND |
| One spray gun | 10 to 15 SCFM | 20 SCFM | 20 to 25 SCFM | 5 to 50 SCFM |
| Two guns plus two DA sanders | 30 to 40 SCFM | 42 to 50 SCFM | 50 SCFM | 5 to 50 SCFM |
| Two painters with supplied-air hoods | 40 to 60 SCFM | 65 SCFM | 65 to 75 SCFM | 65 to 250 SCFM |
| Booth plus prep station and blow-off | 60 to 80 SCFM | 85 to 90 SCFM | 100 to 105 SCFM | 20 to 250 SCFM cycling |
| Production booth, four guns | 80 to 100 SCFM | 105 to 110 SCFM | 125 SCFM | 65 to 250 SCFM |
| Booth fed from a 10 hp piston compressor, no aftercooler | 35 to 40 SCFM | Aftercooler plus 42 to 50 SCFM | Aftercooler plus 50 SCFM | 7.5 to 10 hp piston page |
Non-cycling dryers for booths that spray all day
Production finishing lines keep the guns busy most of the shift, and a 20 to 125 SCFM non-cycling dryer holds 38°F continuously on 115 V. The 25 to 50 SCFM cabinet units and the direct-expansion line from 10 SCFM up both fit on a wall bracket outside the booth.
- 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.
Cycling dryers and filters for shops that spray in bursts
A collision shop sprays for twenty minutes and then sands for an hour, so a 30 to 130 SCFM cycling dryer rests between coats. Behind either dryer the filter set is the same: 1 micron prefilter, 0.01 micron oil-removal coalescer, activated carbon for oil vapor.
- 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.
- HF Series Filters: Modular inline filter family in 22 housing sizes from 20 to 21,250 SCFM; one housing, seven push-on element grades from bulk-liquid separator to activated carbon.
Installing the dryer and filters for a booth
The dryer and filters go outside the booth in a clean area, the drops inside the booth are short, and the filter order is fixed: prefilter, dryer, coalescer, carbon.
A spray booth is an electrically classified area, and a dryer with a compressor, fan and controller does not belong inside it. Put the set in the compressor room or the mix-room corridor and run a dedicated line to the booth drops. The 1 micron prefilter ahead of the dryer removes bulk oil and rust; the 0.01 micron coalescer after it takes oil aerosol down to under 0.01 mg/m3; and the activated carbon element last removes the oil vapor a coalescer cannot see, the vapor that recondenses on cold panels and makes craters. Change the carbon element by hours, not by pressure drop, because it never blocks.
Give the set a bypass so the shop can spray primer during an element change, and drain every bowl to a container, not the floor of a finishing area. Where painters wear supplied-air hoods, their line takes a breathing-air filter package of its own after the dryer; the dryer removes the water, not the carbon monoxide.
Two painters with hoods are the 65 SCFM dryer at 100°F and the same 65 in a hot room only if the mix room stays under 105°F; past that it is the 75 or 85.
Size a dryer for my paint booth
Clean, dry air for a spray booth
By hours in service, not by the pressure gauge. Carbon adsorbs vapor rather than trapping particles, so it never blocks and the pressure drop stays flat while the element quietly saturates. Log the hours from installation and change it before the 1,000-hour mark; a shop that waits for craters on a panel has already repainted a job. Change the coalescer ahead of it at the same visit.
Summer air carries more water and the compressor room runs hotter, so the dryer is working at a higher inlet temperature and a higher ambient at once. A dryer sized to the cool-weather load passes water during long spraying sessions in July. Check the mix room or compressor room on a hot afternoon; past 105°F the booth duty needs the next size, as the hot-room column on this page shows.
Powder wants the same dry, oil-free air, and for a stronger reason: damp powder clumps in the hopper, feeds unevenly and spits at the gun. A 38°F refrigerated dryer with the 0.01 micron coalescer and carbon set covers a booth in a heated building. Size it from the fluidizing air, the guns and the blow-off together, since the hopper draws air continuously while the line is running.
Only if the booth branch gets its own filters after the split. Shop tools tolerate a little oil and a finish does not, and a shared coalescer that loads up from lubricated tool lines will pass oil to the guns. Run a dedicated line to the booth with the coalescer and carbon element on that branch, so a missed filter change on the shop side never reaches the paint.
It follows the load down. A collision shop sprays for twenty minutes and then spends an hour sanding and masking, when the draw falls to a sander or two, and a cycling unit stops its refrigeration compressor and rides on its thermal mass until the guns start again. A non-cycling dryer runs at full power through all of it. The dew point at the gun is the same either way; the difference is the power bill and the hours on the refrigeration compressor.
Give the booth line a slight fall back toward the filter set and keep the drop inside the booth short. A low point near the gun collects whatever condenses after the dryer and delivers it as a slug the first time the trigger is pulled, usually onto a fresh panel. Put a drain leg with a valve at the bottom of each drop so any water has somewhere to go, and open it at the start of every shift.
