Screw Compressors and Oil Loss In Industrial Refrigeration

Joshua Rees is an industrial refrigeration technician, father of six stunning kids and a husband to his stunning spouse Jessica.  Joshua has been within the trade since sixteen and began his profession within the industrial HVAC/R trade. 

Throughout a dialog with a few of my friends, the topic was introduced up about oil loss in screw compressors. The opinion was expressed that the oil cost on a screw compressor would must be “topped off” each few months and that this was frequent upkeep amongst refrigeration amenities. On account of that dialog, I’ve determined to precise my private opinion with regards to oil loss in screw compressors.

All through my years in service and facility operations within the industrial refrigeration subject, I’ve heard many opinions on oil loss/migration. Plenty of operators consider that replenishing your oil cost is one thing that happens regularly. In my view, it is a false impression and nearly at all times leads again to technicians which might be used to (or educated by somebody that was used to) the “Vilter” or “Fuller” days. We have all been there. These compressors bypassed giant quantities of oil on an annual foundation. It was the “Nature of the Beast” so to talk. Then we began to see the dual rotary screw compressor. Big compressors that have been extra environment friendly with giant separators on them. With all the additional coaching that got here together with these machines (or lack thereof relying in your employer), one factor that was by no means really centered on was oil utilization and coalescing filter effectivity.

So, the very fact of the matter is, coalescing filters are extraordinarily environment friendly if put in appropriately. I’ve had compressors go years with no need oil added to the machine. Some information that I’ve discovered means that they solely cross a few tablespoons of oil on an annual foundation (relying on the effectivity of the filter). Numerous gradual oil loss points that I’ve seen boils down to at least one factor sometimes, incorrect set up of coalescing filters. One producer specifically is essentially the most inclined on the subject of this subject. They’re infamous for passing oil from day one. The explanation for it’s because, not like their opponents they’ve not put in information bars to simply align the filters throughout set up. Now are you able to think about throughout startup having 20 or extra of those filters to put in? They most likely weigh round 25 lbs. on common! Now think about, kneeling, one arm prolonged into the separator (as a result of the opposite one must be free to put in the nut) bearing all the burden of this coalescing filter within the palm of your hand, after which transferring it up and all the way down to insure that it’s sitting flush in opposition to the again wall. It’s exhausting! In case you’ve ever been in weight class and did a typical train known as pyramids, you’ll understand how this feels. You may see large guys wrestle to elevate a forty five lb. weight bench bar as a result of repetitions. It’s the identical factor. Now don’t get me incorrect, I’m a fan of that model of compressors. They’re reliable, nice, lengthy lasting machines. Their coalescing filters are nice additionally. The one subject is the means to put in them should not fairly pretty much as good as a few of their opponents. And this doesn’t imply that the opposite makes should not inclined to the identical subject, I’ve simply seen it extra with with this explicit model and that’s my unbiased opinion.

Oil separator instance from Bitzer

Among the different points that trigger gradual oil loss may be that your oil return valve shouldn’t be opened sufficient. The quantity of oil “smoke” that’s handed between coalescing filters will change relying on load and velocities. As a result of this truth, you could possibly see a rise in oil amassing within the coalescing aspect of your separator. I’ve truly had this subject a number of instances and the repair is only a small adjustment to your oil return valve. One other frequent subject that I’ve seen is the truth that lots of people overfill compressors throughout oil modifications or “prime offs”. Frick’s suggestion is to run the working degree between the 2 sight glasses. That implies that throughout an oil change or “prime off”, you need to run the oil till you simply see it come into the highest sight glass. What this may stop is the spilling over of the oil into the cavity that’s between the oil separator and the coalescing filter wall. That is additionally a typical method to shorten the lifetime of the coalescing filters. As everyone knows, any liquid that goes right into a coalescing filter probably can injury them or “blow them out” relying on the quantity. So if you’re filling up your separator each month or two and you’re filling it as much as the highest of the sight glass, after a few instances, you could possibly be pushing oil into the coalescers.

In closing, I clearly didn’t focus on all of the methods you possibly can lose oil. I needed to concentrate on just a few points that I’ve seen all through my profession that’s one thing I take into account frequent misconceptions about gradual oil loss in screw compressor packages. You probably have any questions relating to this text, please shoot me an e mail. This text is strictly my opinion and relies off of my private expertise within the subject (and fairly just a few hours of analysis and coaching). I’ve copied an inventory from Gartner refrigeration to offer a whole record of oil loss points and pasted it beneath for everybody’s reference additionally.

Sudden oil loss by means of the suction port:

■ Suction test not holding will trigger the compressor to again spin. Oil travels up suction line and dumps into the system. → Look ahead to coupling rotating backwards → Restore test valve

■ Suction test valve by-pass line is opened too far.

Steady oil loss by means of the economizer port:

■ That is generally brought on by the economizer test valve not holding. Oil can find yourself migrating from one compressor to a different. Restore the test valve or take into account changing it with a piston model test valve.

Steady oil loss by means of the discharge port:

■ The coalescing parts are the almost definitely explanation for this. Oil finally ends up going to the condensers, and is carried again by means of the remainder of the system. → Defective / worn coalescing parts; exchange coalescers → Coalescing parts could also be unfastened; not put in appropriately → Bulkhead is a clean plate; test gasket for leaks

■ Oil can be the issue with discharge port loss. → If the oil is foaming, then the oil may be carried out in foam → Flawed sort of oil getting used → Various kinds of oil getting blended within the compressor → Liquid injection not set correctly → Oil cost maintained too excessive; decrease the oil degree

Working situations could cause steady or sudden lack of oil:

■ Differential strain too low inflicting excessive velocity throughout the separator.

■ Discharge strain is decrease than unique design, inflicting vapor velocity within the separator to be too excessive.

■ Sudden drop in discharge strain could cause oil foaming.

■ Liquid carry over or slugging fouling the coalescing filters.

■ Coalescing oil return to compressor not functioning. → Valve closed → Valve or line plugged

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