Oil Recovery System - HELP!

[manuelcm]

Hi. I'm currently working on a system as the one shown schematically in the picture below.

I need help or advice on designing/Choosing the appropiate oil recovery system. Given that the compressor is situated in the highest point of the circuit, after some time operating, oil will tend to stay in the lower part, thus leaving the compressor dry.

I´ve thought of a U shaped oil trap on the discharge line, and maybe a capillary tube that comes out of it to return the oil. But I haven't had luck searching for a similar system. So, any help or idea would be greatly appreciated.

[US Iceman]

manuelcm,

You need to search for some information on dual suction risers and traps. I think there is some of this information on this site.

[Peter_1]

I´ve thought of a U shaped oil trap on the discharge line, and maybe a capillary tube that comes out of it to return the oil. But I haven't had luck searching for a similar system. So, any help or idea would be greatly appreciated.

The U-trap must be installed in the suction line, not the discharge line and make that speed is high enough in the vertical riser.

What's the height difference anyway?

If your compressor has no partial load system and runs always full-load, then you even don't need - in my opinion - a double riser.

[Cofreth]

How about adding an oil separator immediately after the compressor hot gas discharge line.

[Tejbir Singh]

i am also facing similar problem in one of trane's RTHD type screw chiller. although trane has provided gas pump to rectify the problem but when oil flow sensor shows dry and sump has no oil it needs external help of an oil pump. can any body inform me where to fix this pump as trane's manual do not describe it.

thanks & Regards
Tejbir singh

[manuelcm]

Hi Everyone, thanks for the replys.

To peter1: Thanks a lot for your interest. Excuse me for my ignorance, but Why is it that the trap musto go on the suction line? When I start my compressor, oil tends to leave through the discharge line. If I was to put the trap on the suction line........The compressor would run dry anyway, wouldn't it? because the oil won't be returning to be trapped. The main problem is that it's 3 metres above the floor. The compressor is a wobble plate compressor, It's very simple, and when the oil level goes down, there's nothing you can do other than adding some oil.

The sad thing, is that I'm not allowed to change the copmressor.

[refteach]

It is harder to separate oil out of the discharge of the compressor, the oil droplets are hot and the viscosity of the oil is low and will not readily form droplets, it mainly resembles a mist or fog rather than droplets. The main principles of oil separation in the discharge line are impingement, lowering of velocity, direction change and gravity. There are several types of discharge oil separators out there with separation techniques ranging from demister pads, coalesing elements to helical type. I mainly deal with large industrial ammonia equipment but I know that Henry makes smaller type oil separators for use on the discharge of compressors. Here is a link to one of their Tech Tips on the subject.

http://www.henrytech.com/techtips_pdfs/HT-TT4.pdf

Part of the reason that your oil may leave at start up is you may have refrigerant condensed in your oil. The combination of lowering the pressure and the agitation causes the refrigerant to boil and foam the oil. Adding a Crankcase heater to raise the temperature of the oil will keep the refrigerant from condensing. The industrial compressors I work with have a minimum starting temp of 100 F because of this (which should hopefully be above ambient temperature in the engine room). Its amazing to watch 5 gallons depart a crankcase in less than 3 minutes when it is too cold at start up .

[Josip]

Hi,

Hi Everyone, thanks for the replys.

The compressor would run dry anyway, wouldn't it? because the oil won't be returning to be trapped. The main problem is that it's 3 metres above the floor. The compressor is a wobble plate compressor, It's very simple, and when the oil level goes down, there's nothing you can do other than adding some oil.

The sad thing, is that I'm not allowed to change the copmressor.

Yes you must add some quantity of oil until noticed that oil is coming back. It is hardly to say how much oil you must add until you establish oil recirculation but that is normal procedure if your pipes are a little longer.

Of course complete design (pipe diameters, risers single or double and other things) must be done properly to assure oil return and that can be the hardest task in designing of refrigerant plant. If this is wrong you can add oil as much as needed into compressor but without oil return your evaporator will stop to cool and then you have to drain oil.

Changing of compressor will not make return of oil, maybe you can have a longer time until next adding of oil into crankcase

Replay and link given by Refteach is very good.

Best regards, Josip

[manuelcm]

Hi again.....Thanks so much for the feedback........amazing what Refteach said about that massive amount of oil leaving so fast!!!.

I think I sort of have the same problem, My compressor is designed to be used under the hood of a running car, for A/C.....where temperatures might be between 122 to 175°F I guess.............Maybe I´m just starting it too cold.............I´m more into other areas of engineering than HVAC, and I'm not really experienced in this, so I woldn't have thought about that straight forward, and now It seems so obvious, d'uhhh!

Even so, I think I still need some kind of device to separate the oil, and I'd rather build something myself (I'm on a tight budget !) than buying it.

I found some DIY oil separators on the web, I don´t know what you think about.........

[slingblade]

What on Earth are you working on? a compressor from a car cobbled to system components from other applications is a new one on me.
as Peter said, an oil trap should be in the suction at the evap. outlet. as this is the lowest point on the system when it fills with oil and no gas can pass through the oil will be sucked back to the compressor up the suction line.

[Samarjit Sen]

You should install a good Oil Seperator like Temprite in your system immediately after the compressor discharge. If you can provide the details such as the Compressor capacity, Suction Temp. Discharge Temp. and the Compressor displacement, may be I could suggest the proper Temprite model and the system design . From your sketch the vertical height is 3 m. Please state what is the horizontal length. You may also contact www.temprite.com