It is widely believed that the oil on a screw compressor needs to be topped off every once in a while as part of the maintenance process for refrigeration facilities. The reality is that if coalescing filters are installed correctly, they are very efficient, so compressors can go years without you having to add oil to the machine. Depending on the efficiency of the filter, some compressors only pass a couple of tablespoons of oil each year, and in most cases, gradual oil loss occurs as a result of incorrect installation of coalescing filters.
Guide bars can easily align the filters and must be part of the installation process, so if you notice that your machine is passing oil, this can be the reason why. There are, of course, other issues that can cause gradual oil loss and an oil return valve that is not opened enough is one example. The amount of oil that is passed between coalescing filters will change based on load and velocities, so you may see an increase in oil accumulation in the coalescing side of your separator. The fix is easy enough and is usually a small adjustment to your oil return valve.
Overfilling compressors during oil changes is another common issue that you can avoid by running the operating level between the two sight glasses. During an oil change, run the oil until you see it come just into the top sight glass because this will prevent the spilling over of the oil into the cavity located between the oil separator and the coalescing filter wall. Failing to do this will also shorten the life of the coalescing filters because any liquid that enters a coalescing filter can potentially damage them or even blow them out, depending on the amount.
If you experience sudden oil loss through the suction port, it may be a sign that you need to repair the check valve or it may be an indication that the suction check valve by-pass is opened too far. If you experience continuous oil loss through the economizer port, it’s likely because the economizer check valve is not holding. This can cause oil to migrate from one compressor to another, so you need to repair the check valve or consider replacing it with a piston style check valve. Continuous oil loss through the discharge port means there is a problem with the coalescing elements, and if oil ends up going to the condensers, it will get carried back through the rest of the system. Faulty coalescing elements need to be replaced, and you should also check the gasket for any leaks.
Operating conditions can also cause continuous or sudden loss of oil, and the experts at HECO Ltd can provide you with more information. We have years of experience in this field, so we can answer all of your questions. If you are interested in more details, contact us today!