company news about Why Oil Moisture and Filter Delta P Dictate the Life of Your Screw Compressor

If you run a screw refrigeration compressor in an industrial refrigeration or cold storage setup, you already know that oil does most of the heavy lifting. Beyond lubricating the bearings, it seals the gaps between the rotors and absorbs massive amounts of heat. But because that oil is constantly exposed to refrigerant, your compressor maintenance routine is only as strong as your oil chemistry.

Here is how to read the warning signs before a minor oil issue turns into a catastrophic system failure.

Water is the ultimate quiet killer of synthetic lubricants. If your system uses polyolester (POE) oil, remember that these oils are highly hygroscopic—meaning they pull moisture out of the air like a sponge.

Once your water content creeps past 50 ppm (which we measure strictly via ASTM D6304 Karl Fischer titration), things go south quickly:

The moisture triggers hydrolysis, literally tearing the POE oil's chemical bonds apart to create organic acids. In a semi-hermetic compressor, this acidic sludge starts eating away at the protective insulation varnish on your stator windings. The end result is almost always a costly motor burnout.

That is why we draw a hard line at a Total Acid Number (TAN) of 0.1 mg KOH/g. Anything higher means your oil is compromised, and you need a complete system flush.

Protecting those high-precision, 5:6 asymmetrical rotors means trapping metal shavings and debris before they can score the rotor surfaces. While we rely on 10-micron fiberglass filters for this, you cannot rely on guesswork to decide when to change them.

Instead, watch the differential pressure Delta P across the filter housing.

Under normal, clean-running conditions, you should see a pressure drop between 0.03 MPa and 0.08 MPa. But once that reading hits 0.15 MPa, your filter media is choked. If you ignore this limit, the compressor's internal bypass valve will open to keep the oil flowing to the bearings. The catch? It will be pumping dirty, unfiltered oil directly onto your rotors.

As a rule of thumb, always swap out the oil filter after the first 500 operating hours of commissioning, and then stick to a strict schedule of every 3,000 to 5,000 operating hours after that.