Reciprocating Compressor - Process Tube for Oil Return (from oil separator)?

Greetings!

As stated in the title, I'm considering using the process tube as an oil return line from the oil separator. Now it has occurred to me that this might cause a hydraulic knock in the compressor.
The separator is at the HP side. Picture attached.Attachment 14800

It is for my own experimental project

Any thoughts?

Compressor: Tecumseh AK5515ES , Retrofitted to R134a
Oil Separator: EKS OS-1012 2,3L - float valve activated

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Icer,
Where will you return the oil to?
Does it really need an oil separator on such a small system!

Icer
It is quite normal to use the process tube for oil return on hermetic machines,or you could just inject it into the suction pipe work about 500mm from the compressor suction. As Ranger says it is strange to fit an oil separator onto such a small package unit unless your evaporating at extremely low temps

Hello again and thank you for your answers!

The system does not need an oil separator, (evaporation temperature about 0°C) but since it is a kind of personal project and experiment, I wanted to get one (fitting a sub-cooler was also kind of exorbitant for such a small system). I wanted to see if I would improve the heat transfer rate in the heat exchangers by removing oil from the hot gas and wanted to get some more volume on the high pressure side (to minimize early cut-outs?).

Is it better to fit the oil return to the suction line? I'm no expert, but it seems to be a better idea than attaching it to the process line. Could an oil return to the process tube cause compressor knocking? Is a 1/4'' tube usually used for such applications or do I need a capillary? (we are talking about max 1 m distance)

Hi Icer
I've never heard of a problem with oil return via the process tube, so either suction or process line would work without problems. 1/4" tube is quite normal on this size of unit for oil return, capillary tube for oil would most probably not work due to viscosity .
I was looking at your drawing and it shows 2 types of expansion valves ,they look like Danfoss T2 and AKV. If it is an AKV you should not use it on a plate HE as during the AKV off cycle the plate could go into a vacuum and cause LP issues. Would suggest you change it to an ETS6 valve which works much better on plate HE's

Quote:

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Originally Posted by Glenn Moore

I've never heard of a problem with oil return via the process tube, so either suction or process line would work without problems. 1/4" tube is quite normal on this size of unit for oil return, capillary tube for oil would most probably not work due to viscosity .

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Hi Glen, thank you for the answer and the hint!

Quote:

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Originally Posted by Glenn Moore

I was looking at your drawing and it shows 2 types of expansion valves ,they look like Danfoss T2 and AKV. If it is an AKV you should not use it on a plate HE as during the AKV off cycle the plate could go into a vacuum and cause LP issues. Would suggest you change it to an ETS6 valve which works much better on plate HE's.

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The reason for the 2 Expansion valves in the Evaporator circle is that I'm programming my own controller. TEN2 valve will regulate the heat pump without an external controller. The ETS6-12 is the valve shown, it will be used to test the heat pump driven by my control system. Both expansion valves can be isolated via ball valves.
The expansion valve on the inter-cooler is the TN2.
The reason I chose the ETS6 over the AKV is pretty trivial - my total inexperience and unfamiliarity with/of PWM regulation in practice (on-off regulation is not really something I would trust, didn't really "feel right" so off the hat).

Hi Icer
The AKV are fine on normal air blowers and supermarkets but no good with plates, the ETS 6 works well just be sure not to undersize it capacity wise as there is no spare capacity unlike its T2 equivalent
Hope it works well , Glenn

Hi,
What I have experience is that R-134a,R-12, MO49 & MP 39 moves with oil in system and it return back to Compressor where as other gases like R-22 & 4 Series have a problem that they lift up the oil from compressor and left it in Evaporate (Special in case of minus temp. below 0C) which case choking /blockage in pipe and form an ice due to which Compressor got Damage.
But here I don't think you need oil Separator .

If I am wrong please let me know dear friends

Hi Rahul
The 4 series of refrigerants often are quoted as mineral oil is comparable, but in many cases with the likes of R422D etc mineral oil often fails to return to the compressor. The simple answer is to use a POE equivalent lubricant with these refrigerants which should cure the problem. I know of engineers who have put POE lubricant in with the mineral oil charge to encourage oil return which seems to work. As a rule of thumb systems with long pipe runs or systems that evaporate lower than minus 15C should have an oil separator fitted