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Quotes - Engineering - SalesWater Separators for Compressed Air Dryers
Centrifugal and impaction separators that take the bulk water out before the dryer sees it
Between the aftercooler and the dryer the compressed air carries liquid water: the condensate the aftercooler produced, the water that fell out in the receiver and the pipe, and on a piston compressor a good deal of slug. A separator takes that liquid out mechanically, with no element to saturate, so the dryer's exchanger and the prefilter's coalescing element only have to deal with what is still vapor and aerosol. That cuts the dryer's refrigeration load and roughly doubles prefilter element life.
Two designs are cataloged. The centrifugal separator spins the air through a finned module so the water is flung to the housing wall and shielded from re-entrainment, removing 99 percent of bulk liquid across the flow swing of a variable-speed compressor; thirteen threaded housings cover 6 to 1,500 SCFM and a 4 in flanged unit reaches 3,000. The impaction separator fits a grade 11 element into the modular filter housing family, forcing the air through direction changes that throw out water and solids down to about 10 micron, from 20 to 21,250 SCFM.
Both are rated for the pressures and temperatures of plant air, 232 to 300 psig and 150 to 176°F, and both discharge through a float or automatic drain in the bowl. The separator is installed in the pipe run before the dryer, as close to the dryer inlet as the layout allows, so it catches the water that condenses in the line.
- Centrifugal separation, 99 percent of bulk liquid, no element to replace
- Impaction separation to 10 micron in 29 housing sizes to 21,250 SCFM
- 232 to 300 psig ratings, 150 to 176°F, automatic or float drains
- Installed after the aftercooler or receiver and ahead of the dryer prefilter
The two separator series
Flow range, pressure rating and the number of housing sizes in each series. Open a series page for the housings, connections and drain options.
| SERIES | TYPE | FLOW RANGE | PART NUMBERS | NOTES |
| GF WS Series Separators | Water Separator | 6 to 3,000 SCFM | 14 listed | 232 psig max |
| HF Grade 11 Separators | Water Separator | 20 to 21,250 SCFM | 29 listed | 300 psig max |
Separator series
Centrifugal or impaction
The centrifugal separator has no internal parts to wear or change: the air enters tangentially, spins, and the water leaves through the drain. Its separation depends on velocity, so the housings are sized close to the actual flow, though the design keeps working across the wide flow range of a variable-speed compressor. The impaction separator uses a pair of stainless orifice tubes as its element, which does wear eventually and is replaced like a filter element, but it shares housings, connection codes, brackets and option letters with the modular filter family, so a plant already standardized on those housings keeps one set of spares. Both remove liquid; neither removes aerosol, which is the prefilter's job.
Sizing and pressure drop
Size the separator on the compressor's delivery at line pressure, the same figure used for the prefilter. A clean separator adds under 1 psi, and because there is no media to load, that figure does not climb with time. The centrifugal housings run from 1/8 in NPT at 6 SCFM to 3 in NPT at 1,500 SCFM, with the 3,000 SCFM unit on a 4 in flange; the impaction housings follow the filter family from 3/8 in NPT to 10 in ANSI flanges on the ASME vessels.
Where a separator earns its place
Every installation with a water-cooled aftercooler, because the aftercooler makes the most condensate on the coldest water. Every piston compressor with an aftercooler, because the pulsing flow carries slugs. Any long pipe run between compressor room and dryer, because the pipe is an aftercooler too, and any plant whose compressor package has no integral separator. A rotary screw package with its own moisture separator and a receiver ahead of the dryer may not need a second one, and the money is better spent on the next size of prefilter; raise it when the layout is being quoted.
Drains and installation
A separator that is never drained is a pipe fitting, so the drain matters as much as the housing. The centrifugal housings carry an automatic float drain; the impaction housings up to 170 SCFM ship with an automatic drain and liquid level indicator, the mid sizes with an indicator and a drain plug for a separate drain, and the large sizes with a drain plug. On a plant that runs continuously, fit a zero-loss drain so no compressed air is vented; a timed drain wastes air on every cycle. Mount the separator upright with the drain at the bottom and give it a short straight inlet run, and put the 1 micron prefilter immediately after it.
Taking bulk water out ahead of the dryer
Look at the next bowl. Liquid standing in the prefilter immediately after the separator, an element that goes heavy and wet weeks early, or dew point spikes that come and go with the compressor cycles all point upstream. The cause is nearly always the separator's drain rather than the separator, either stuck shut or too small for the condensate arriving. Fix or upsize the drain first; a centrifugal housing has nothing inside to wear out.
Not enough to argue about. A clean separator costs under 1 psi, and because there is no media inside to load with dirt, it stays there for the life of the housing. That is a different picture from a coalescing element, which starts low and climbs until it is changed. Size it on the compressor's delivery at line pressure and the drop takes care of itself; an undersized body is the only way to make it matter.
Yes. The colder the cooling water, the more water the aftercooler condenses, and in winter that can be the heaviest condensate load of the year. Without a separator that liquid rides the pipe to the dryer as slugs, overwhelming its internal separator and its drain. A separator after the aftercooler or receiver catches it while it is still bulk liquid, which is the cheapest place to take water out of compressed air.
No. Both designs depend on gravity once the water has been thrown out of the airstream: the liquid runs down the housing wall to the drain at the bottom. Tilt the housing or lay it on its side and the collected water sits where the air can pick it up again, so separation falls off. Mount it upright, give it a short straight inlet run, and leave room underneath to service the drain.
The impaction separator, because it is a grade 11 element dropped into the same housing family. It shares connection codes, brackets and option letters with the filters, so one stock of heads, bowls and seals covers both, and the range runs from 20 to 21,250 SCFM. The trade-off is an element that wears and must be replaced, where the centrifugal design has nothing inside to change.
It removes liquid oil along with the water, as one mixture, but it does not split them and it does not touch oil aerosol, which stays in the air for the coalescing prefilter. Whatever the separator drain discharges is therefore oily condensate. Pipe it to an oil-water separator rather than the floor drain, and expect a lubricated compressor to put a visible oil sheen in that discharge.
