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rublet
09-05-2006, 09:07 PM
Hello,
New to the forum so I'll get my first question under way hope its not been asked somewhere else.

Can anybody explain the principal of the oil separator (how the oil gets in how it returns to the compressor and when and reasons why it should'nt) and function of the float etc. Also are there any web sites that may enlighten me?
Any help much appreciated.

NoNickName
09-05-2006, 09:34 PM
Some refrigerants like R404a have a low isoentropic exponent, that causes a lower discharge temperature per compression ratio. A lower discharge temperature will in turn results in a higher oil carry over because of dilution.
In the run, compressor may starve because of this. As oil builds up in the colder part of the refrigeration circuit, like evaporator, it will become denser, like molasse, and will not be carried by refrigerant back to the compressor.
In order to avoid this scenario, an oil separator is added in order to trap the oil until it's warm and return it to the compressor.
The float controls the discharge oil solenoid and refills the compressor: high float opens to return excess oil, low float closes to prevent hot gas bypass.

Peter_1
09-05-2006, 09:42 PM
http://www.temprite.com/downloads/temprite/CoalescDemoPrimary_files/frame.htm

http://www.temprite.com/main_content.asp?sitename=temprite&pagename=resources

http://www.esk-schultze.de/oil_separator.pdf

http://www.henrytech.com/faqs.cfm

Once you have read all this :D

rublet
09-05-2006, 10:17 PM
cheers guys thanks for the response.

A few more things though, the oil diff switch please explain the function etc and with the oil sep the return pipe i presume is under no pressure from the refrigerant?

rublet

Brian_UK
09-05-2006, 10:28 PM
The oil pressure switch monitors the oil pressure within the compressor. It relates the normal oil pressure with the refrigerant pressure in the compressor otherwise it would give false readings.

If the oil pressure is not established within a set time after compressor start up then the oil pressure switch will trip off the compressor to protect it.


The oil separator is at discharge pressure; the return oil line to the compressor connects with the low pressure side hence the differential pressure between the two moves the oil back to the compressor crankcase.

Also, welcome to the forum, if you'll add your location to the RE Members Map we'll know where to find you!!

Dan
10-05-2006, 12:39 AM
A few more things though, the oil diff switch please explain the function etc and with the oil sep the return pipe i presume is under no pressure from the refrigerant?

Just in case Brian's excellent answer was a step beyong your question:

The oil differential switch (oil safety control) only comes into play when there is a dedicated oil pump to circulate the oil. Depending upon the manufacturer, the "oil safety control" will permit the compressor to operate if it senses a positive output pressure from the oil pump when compared to suction pressure (oil sump pressure). This is for compressors designed to move oil toward bearings and other key wearing surfaces.

Small compressors do not have such devices and rely upon slinging the oil to the surfaces requiring lubrication. Others, such as scroll compressors, rely heavily on maintaining an oil level, or as in the case of screws, maintaining a rate of flow.

The oil return pipe may be high pressure or low pressure, but by the time it enters the compressor crankcase, it will be at or near suction pressure. Refrigerant pressure is important in this process, since there can be significant amounts of liquid refrigerant mixed with the oil. This is where you might see excessive foaming, or washout of oil.

Oil should feed into the compressor by maintaining a higher pressure than the suction pressure. A small differential is all that is needed to insure flow.

cool breeze
10-05-2006, 02:11 AM
This is Cool Breeze and I am new to the forum. Want to add a bit of info. to the oil separator question. Separators can also be used on systems with different types of capacity controllers or unloaders. In low load situations where the system runs unloaded, the refrigerant velocity will drop and on long runs or situations where the A/H is located on the roof and cond. unit on the ground you will not have to worry about oil return.

Peter_1
10-05-2006, 06:34 AM
I allways found this a good booklet
http://www.danfoss.com/NR/rdonlyres/54357ACD-2306-406E-BC74-8942D95A73DF/0/RG00A502.pdf

hendry
19-12-2007, 12:12 PM
adding to it ...

oil pressure line for some compressor comes after oil has passed the crankshaft and close proximity to mech seal.

while for screw comp, it can be before oil pump or after, but both is in used in the controls.

pressure switch has different preset timing i.e 45s, 60s and 90s.

for oil sep, you can have cyclone & filter type.
cyclone works on gravitational forces of the oil droplets.
filter = need element of different micron size ... screw comp will use mostly coalescing element to produce as close to 99.99% filtration on lube oil in the discharge line.

crankcase pressure is higher than suction presure due to contribution from oil return line from oil sep if we are talking about reciprocating comp.

cheers ..

Pinnacle
22-06-2008, 10:16 AM
Hi Guys, i'm new to this site but am already finding it of interest, use and benefit.
On the subject of oil separators but off on a bit of a tangent, i'm looking for a small in line oil separator to use on the suction line of a small multi refrigerant oil less recovery unit.
Can anyone here point me in the right direction?
Keep smiling everyone!

nevgee
23-06-2008, 02:01 AM
Simple point but quite fundimental ....... All compressors due to thier very nature will pump gas but, they depend on a lubricant to ease the motion of the parts. This lubricant inevitably gets moved through the compressor and is discharged with the gas at the discharge port.
On many aic con units the extent of the refrigeration circuit is adequately designed to allow the oil to return through the circuit. On other systems, typically heat pumps, commercial and larger sytems there is a need to prevent the oil going on a walk about, so we fit oil seperators at the discharge of the compressor. The seperator catches the oil an returns it directly to the compressor. If this wasn't done then the compressor sump would be emptied of the oil charge, and more oil would be need to top up the system. The seperator helps by catching the oil and maintaining an adequate oil level in the compressor.