Filtration separation equipment can look interchangeable from the outside, but the unit that keeps your plasma cutter's air dry won't keep your machining coolant clean-and neither will produce nitrogen for a draught beer line. Before you spend anything, decide whether you're protecting compressed air, extending cutting fluid life, or generating process gas. That choice narrows the field faster than any spec sheet.
Quick take
For shop air feeding a plasma cutter or paint spray, the 3/4-inch NPT air dryer is the practical choice. For a machine tool running liquid coolant, the oil-water separators from Maisutseb and TECHTONGDA are the matched solution. For beverage or industrial nitrogen, the Green Air membrane can work, but expect a used component rather than a standalone generator.
Comparison table
| Product | Listed Price | Price Bar |
|---|---|---|
| Green Air Nitrogen Membrane Separator | USD 1,500.00 | |
| Maisutseb Oil-Water Separator | USD 1,886.00 | |
| TECHTONGDA Oil-Water Separator | USD 1,886.00 | |
| 3/4-inch NPT Air Dryer | USD 158.00 |
Decision matrix
| Your Need | Recommended | Why It Fits |
| Dry compressed air for plasma cutting or paint equipment | 3/4-inch NPT Air Dryer | Direct match for a compressor water-separation task |
| Clean and extend cutting fluid on machine tools | Maisutseb or TECHTONGDA Oil-Water Separator | Built specifically for floating-oil removal from coolant |
| Inert gas for beverage or process lines | Green Air Nitrogen Membrane | Made for high-demand draught beer nitrogen supply |
Product notes
#### Green Air Nitrogen Membrane Separator
For a facility that already has a nitrogen compressor and storage, this Green Air membrane is the part that separates nitrogen from the air stream. It came out of a draught beer installation and is being sold used as the membrane only, so you need the surrounding air system and plumbing to make it work. At roughly 45 inches long and 6-8 inches wide, it's a bulk piece of process equipment, and its 200 PSI rating tells you the pressure ceiling. Choose it if you're replacing a similar membrane; skip it if you need a complete plug-and-play nitrogen generator.
#### Maisutseb Oil-Water Separator
The Maisutseb oil-water separator is built for machine shops running liquid coolant on machine tools. It pulls floating oil off the cutting fluid and lets you drain and reuse that oil, which helps the fluid last longer and keeps tooling and the work environment cleaner. This is a new unit, and the task it does is narrow: it's for cutting-fluid maintenance, not compressed-air drying or gas separation. If you need a multipurpose separator, this won't be it. That specificity is also what makes it good at protecting coolant in a dedicated sump.
#### TECHTONGDA Oil-Water Separator
TECHTONGDA offers the same cutting-fluid oil-water separator with the same MPN as the Maisutseb, so the practical difference is the label. The mechanism removes floating oil from coolant, extends fluid life, and helps maintain machining accuracy. Grab the TECHTONGDA version if that label is the one you want on the tank. Its scope is cutting-fluid duty, not air-line drying or gas separation, so match it to your coolant sump rather than your compressor. Like the Maisutseb, it needs 208-240V 3-phase power, so a single-phase shop will need an electrical upgrade before this can run.
#### 3/4-inch NPT Air Dryer
The 3/4-inch NPT air dryer is a new 7-pound aluminum unit for compressed-air lines feeding plasma cutters or paint spray. It combines three filter stages and a desiccant dryer with auto drain, and the kit includes a pressure gauge, connectors, pipe fittings, filter elements, and desiccant beads. It's rated to 240 PSI, which fits high-pressure shop air, and the 3/4-inch NPT ports let you tie into an existing line. The main constraint is orientation: the maker says not to install it horizontally. It is not an oil-water separator or membrane system.
Final recommendation by use case
If your air lines feed a plasma cutter or paint spray, the $158 3/4-inch NPT air dryer covers the basics. If you're maintaining cutting fluid on a machine tool, the matched $1,886 oil-water separators are the ones to start with-choose the Maisutseb or TECHTONGDA label and confirm your shop has three-phase power. For a nitrogen supply, the $1,500 Green Air membrane is a component purchase, not a system; it worked in a draught beer installation and is being sold as the membrane only.
