View Full Version : Oil circulation, oil separator effect

25-05-2003, 01:07 PM
Could somebody indicate approximately ( as % of weight of refrigerant) the weight of oil circulating in a refrigeration system with and without oil separator?

What is the expected operation of an undersized oil separator?

Thank you,


11-06-2003, 04:13 AM
I'm not certain that I understand the first part of your question correctly, but the effect of an undersized separator would be excessive pressure drop, and ineffective oil separation...

11-06-2003, 02:47 PM
I would like to know the approximate amount of oil circulating in a refrigerating system ( as a percentage of the refrigerant mass circulating ) , with and without an oil separator.



11-06-2003, 03:45 PM
That would depend upon numerous factors, it's not based upon a percentage of the refrigerant charge.

11-06-2003, 04:06 PM
The compressor manufacturer will specify the required lubricant charge for the compressor. They usually will have additional information regarding the need for additional oil charge in the instances of long refrigerant linesets, etc.


11-06-2003, 04:12 PM
If it's a system with a separator, the oil charge may be increased slightly to acommodate the necessary charge of the reservoir, the float in the separator, and the oil delivery lines back to the crankcase.

I do doubt that the refrigerant charge itself has much bearing on the oil charge.

13-06-2003, 01:49 AM
It is possible that the refrigerant charge has some corelation on the amount of oil in a system that has no separator. But I have to agree, there are too many other things to worry about to consider this the lynch pin for estimating oil charges.

I am just thinking, if you had a refrigeration system with a properly operating oil charge, you would likely have to add oil if you moved the compressor a mile away, with or without a separator.:)

13-06-2003, 03:20 AM
I have come to the conclusion, that auri's interogotive is contemplative. I believe that he is requesting speculation in regard to the amount of (perhaps) "atomized" lubricant that would circulate throughout a system with the application of an oil seperator vs. the mass or volume of circulating lubricant of a system that would freely allow the lubricant to circulate without restriction or containment.

Am I right.... arui?


13-06-2003, 04:20 AM
It has always been my theory that about 35% of the oil is in circulation at all times, this would be in a vapour state and would not cause any harm. In some of the new hydrocarbon refrigerants this could be less because of the make up of the refrigerants.
Wes Maxfield CM

13-06-2003, 11:13 AM

You are right.I am not asking about a relation between the oil charge and oil circulation , but between the refrigerant mass circulating in the system and oil circulation.

This is because, I found a central R22 system, with 3 compressors. Two compressors discharging to a manifold then to a large oil separator.The oil line of this separator was piped to both compressors.
A third compressor was added: Copeland 50 HP (8DP5000FSD). This compressor has a "small" ( compared to the oil separator mentioned above) oil separator with the oil line connected to the suction line of the Copeland compressor. The discharge line of this compressor is connected to the system manifold .So any oil not trapped in the "small" oil separator will be trapped in the large one.
Additionally, from the large oil separator there is an oil line connected through a Sporlan oil level valve to the oil sight glass of the compressor.

Based on this layout, I was trying to determinate the approximate amount of oil flowing by the return oil line of the small oil separator and by the return line of the big one; because the "small" oil separator seems small for the application and the pressure drop is high( typical of an undersized oil separator).Additionally I was trying to determinate if oil returning from the large oil separator will compensate any deficiency shown by the probably undersized oil separator.

Your comment will be appreciated



22-04-2005, 01:50 AM
Did you ever find an answer to your question about oil circulation?
I have found with R22 that some of the compressor oil went out into the system and the level quickly settled out. With some of the 400 series refrigerants more oil seems to leave the compressor and get carried around through the circuit. The oil level settles out but at a lower level than with R22.
I believe that there is a difference between refrigerants and with the use of an oil separator but I don't have numbers to prove it.

Steve Wright
07-09-2005, 01:27 PM
Oil in circulation is about 1.5-2% of refrigerant in circulation for a reciprocating compressor, no separator. Screw compressors circulate much more. You have to know the compressor CFH convert to pounds of refrigerant then calculate oil in circulation. The above is a rule of thumb Impingement separators (regular) are about 50% efficient. Helical separators are above 80% if sized properly. Coalescing separators are above 95% efficient. Take that number times the factor for the oil separator you are using and compare to no oil separator amount.

08-09-2005, 05:45 AM
Hi their the only experence I have had with R22 is in a chiller application with skimmers and a oil receive with a heater and thermostat to drive off the R22 and return the oil to the compressors.

Greg W
26-09-2005, 12:56 PM
Undersized oil seppartor , means oil logging of the condenser, and evap, poor crank case oil level sabbility , oil dilution, slugg back. poor delta Ts.

Have Fun

09-11-2005, 12:47 PM
Wouldn't it all come down to the miscibility of refrigerant and oil, crankcase pressure and vaporisation point of the oil at a given pressure??????????

We had a glass system to observe at tafe and as the temperature of the crankcase rose so did the amount of oil passed throughout the system.

So, and correct me if I'm wrong, the total oil charge would be determined by crankcase level (determined by manufacturer) and the volume of the separator.(determined by manufacturer) So in a standing system the sight bubble would read full in compressor and the reservoir????????????????????????????????????????????????????/

10-11-2005, 09:33 AM
If it's a system with a separator, the oil charge may be increased slightly to acommodate the necessary charge of the reservoir, the float in the separator, and the oil delivery lines back to the crankcase.

I do doubt that the refrigerant charge itself has much bearing on the oil charge.

Hey have i seen you before.

17-11-2005, 02:25 PM
OI Ya buggar. Nice to see you. I knew it wouldn't talk you long. :)

05-12-2005, 12:28 AM
There is no magic number for the oil in a system as a ratio of the refrigerant. In any system you will reach a saturation level based on the solubility of the oil and refrigerant. For a specific point in a system you can get the solubility of the oil with refrigerant from the oil manufacturer. Some oils and refrigerant are fully emissible and other are not.

As for an oil separator, it will not really have much if any effect on the amount of oil that will saturate the system. A properly sized oil separator will slow down the amount of oil leaving the compressor, but the oil that does get by has to be returned or reclaimed and returned to the compressor. Until you can start returning oil, you will have to reach the level of oil in the system which will allow the oil to return. This is especially true of a DX (direct expansion) system. In a flooded system that utilizes a oil reclaimer or oil still, a poorly operating separator will require a properly operaing oil still and it will cycel more often to keep up with the oil loss.


09-02-2006, 07:46 AM
I don't know the percentage related to the use of an oil separator, but Seltec (auto air conditioner compressor) specifies 3-6%. http://www.seltec.com/ocd.htm


11-02-2006, 10:21 AM
Seltec, an automobile compressor manufacturer, recommends 3 to 6 % oil to refrigerant for their systems.

Don (mayball)