When your process air, coolant, or process fluid is carrying the wrong phase-water in compressed air, oil in cutting fluid, or the wrong gas in a beverage line-the fix is not a single device. This set of four filtration separation products covers four different jobs: a compressed-air dryer/water separator, a cutting-fluid oil skimmer, a nitrogen membrane separator, and a stainless bag filter. Prices range from $158 to $1,703.84, so the first decision is your application, not your budget.
Quick take
If you are drying compressed air for a plasma cutter or paint spray setup, the 4-stage air dryer is the direct low-spend answer. For machine-tool coolant care, the PreAsion oil water separator does one job thoroughly. The Green Air nitrogen membrane is the specialist choice when you actually need nitrogen rather than cleaner air. And for process-water or remediation liquids, the TECHTONGDA bag filter gives you a replaceable-bag housing in stainless steel.
Listed price comparison
| Product | Listed price | Price bar |
|---|---|---|
| 4-Stage Air Dryer / Water Separator | USD 158.00 | |
| TECHTONGDA 1# Bag Filter | USD 528.24 | |
| Green Air Nitrogen Membrane Separator | USD 1,500.00 | |
| PreAsion Oil Water Separator | USD 1,703.84 |
Decision matrix
| Use case | Recommended product | Why it fits |
|---|---|---|
| Drying compressed air for plasma cutting or paint spraying | 3/4\" NPT 4 Stage Industrial Air Dryer Compressor Water Separator for Plasma Cutt | Four-stage moisture removal with a 240 PSI working-pressure rating |
| Keeping cutting fluid free of floating oil on machine tools | 208-240V Machine Tools Industrial Oil Water Separator 3PH Cutting Fluid Skimmer | Purpose-built skimmer with oil recovery and a sludge cleaning valve |
| Producing nitrogen for medical, industrial, processor, or beverage use | Nitrogen Membrane Separator Medical/Industrial/Processors/Beverage | Green Air membrane rated at 200 PSI and used previously on a draught beer system |
| Filtering industrial liquids or remediation streams | TECHTONGDA 1# Bag Industrial Filter 304 Stainless Steel 2\" NPT In/Out 120 PSI | Replaceable 1# bag housed in a stainless steel strainer basket |
Product notes
3/4\" NPT 4 Stage Industrial Air Dryer Compressor Water Separator for Plasma Cutt
This air dryer is built around four stages of filtration and drying for a compressed-air line, with an auto drain and replaceable desiccant beads. It uses two 3/4\" NPT air ports and a 1/4\" gauge port, so it is meant to be plumbed into an industrial air setup rather than a small portable compressor. The aluminum tank keeps the unit at 7 pounds, and the 240 PSI maximum working pressure covers most shop air systems. The catch is that it is not for horizontal installation, which limits your mounting options. It is the lowest-priced unit in this comparison and the most direct pick when wet air is your only problem.
208-240V Machine Tools Industrial Oil Water Separator 3PH Cutting Fluid Skimmer
PreAsion's skimmer solves a specific coolant issue: floating oil on the surface of cutting fluid. It separates the oil, drains it for reuse, and includes a cleaning valve for sludge at the tank bottom, which keeps coolant usable longer and protects machining accuracy. The unit is new and built for 208-240V three-phase power, so it belongs in a shop already wired for that service. It is the highest-priced product here, and the tradeoff is specialization: this handles coolant oil removal, not air drying or particle filtration. If your machine tools see heavy use, the oil recovery is the practical reason to choose it.
Nitrogen Membrane Separator Medical/Industrial/Processors/Beverage
This Green Air membrane is a used component. It was previously attached to a compressor and tanks for a draught beer system and is now offered as the membrane only. It is roughly 45 inches long, 6-8 inches wide, weighs about 30 pounds, and is rated at 200 PSI. For someone who already runs a compressor and storage tanks, this is a way to add nitrogen separation for medical, industrial, processor, or beverage applications without buying a complete package. The limitation is the used condition and the need to supply the rest of the nitrogen system around it. It makes sense only if the membrane is the missing piece in a setup you already own.
TECHTONGDA 1# Bag Industrial Filter 304 Stainless Steel 2\" NPT In/Out 120 PSI
For liquid filtration, the TECHTONGDA bag filter is the most versatile piece in this set. The housing is 304 stainless steel with a stainless steel strainer basket, and the 2\" NPT inlet/outlet makes it easy to place in a process line. It is designed for a single 1# filter bag, so maintenance means swapping a bag rather than cleaning a cartridge. The practical limits are the 120 PSI rating and the single-bag capacity, so it is not for high-pressure or high-throughput flows. It is the right call when the goal is removing solids from water or other liquids.
Final recommendation by use case
Start with what you are trying to remove. For moisture in compressed air, the 4-stage air dryer at $158 is the most targeted and lowest-priced pick. For oil floating in machine-tool coolant, the PreAsion separator at $1,703.84 is the specialist tool, provided your shop has three-phase power. For nitrogen generation, the used Green Air membrane at $1,500 fits only if you already have the compressor and tanks. For general liquid filtration or remediation, the TECHTONGDA bag filter at $528.24 gives you a flexible bag-change setup in this group.
