Coalescing filters are very efficient if they are installed correctly, and it’s possible for compressors to work for years without needing any oil added to the machine. If you are experiencing oil loss issues, it is often the result of incorrect installation of coalescing filters, as this will allow for the passing of oil.
There are, of course, other issues that can also cause gradual oil loss, including your return valve not being opened enough. A small adjustment will help fix this problem because it will help stop the increase in oil that will be collecting in the coalescing side of the separator. Overfilling your compressor during oil changes is another common issue that can lead to oil loss, so you have to be careful when topping off your compressor and must run the oil until you just see it come into the top sight glass. This will prevent the oil from spilling over into the cavity that is between the oil separator and the coalescing filter wall.
It’s also important to note that any liquid that enters a coalescing filter has the potential to damage it or blow it out, so if you are filling up your separator every couple of months and are filling it up to the top of the sight glass, you can push oil into the coalescers. The amount of liquid you fill-up will make a very big difference, so you have to be mindful of this aspect.
There are a number of misconceptions surrounding gradual oil loss in screw compressor packages, so it’s important to be aware of this problem and all the ways that you can lose oil. The following guide will further highlight some oil loss issues you can run into:
- If the suction check valve by-pass line is opened too far, you may experience sudden oil loss through the suction port, and the same is true if the suction check is not holding, as this, too, will cause the compressor to spin back. Oil does travel up the suction line, after which it dumps into the system, so you have to keep a lookout for coupling rotating backwards and must repair the check valve.
- If the economizer check valve is not holding, you may experience continuous oil loss through the economizer port, as oil can end up migrating from one compressor to another. You must repair the check valve or replace it with a piston-style check valve when this happens.
- Faulty or worn coalescing elements can lead to continuous oil loss through the discharge port, as can coalesce loose or incorrectly installed elements.
- If the differential pressure is too low, operating conditions can cause sudden or continuous loss of oil. This can also happen if the discharge pressure is lower than the original design because vapour velocity in the separator will be too high.