Oil from separator - where to?

[chemi-cool]

In many cases, the oil return pipe from the separator, goes back straight to to the compressor and many times when liquid is being charged through the discharge valve, it flows back into the crankcase and causes the oil in it to flush out.

Myself, always connect the oil return pipe to the inlet of the liquid separator and if the system does not have one, to suction line as far as it is comfortable to connect it.

Where do you connect yours and why?

[GHAZ]

hi i normally work on big chillers and after a deep vac, i charge into the liquid line which i can normally pull in about 40kg and then using the recovery machine pump in the rest into the condenser,and liquid line, then start the system which is now almost charged and then just trim it , i find it safer and quicker

[Peter_1]

Always, not mostly to the oil reservoir on packs.
In a good working installation, I don't see how you can charge liquid through the discharge valve. Anyhow, if that small amount of liquid could pass through it and it comes in a so hot separator, I'm almost sure it flashes off immediately to gas. Also due to the construction of the separator, the liquid - if any - is ejected against the warm inner mesh or oil separator channels.
If you bring it back to the liquid separator, then this separator isn't performing its task very well because apparently, liquid could pass through it.
So for me, back to the sump.
But...I never installed an oil separator in my whole life on a single evaporator/compressor application, even not on long lines or freezers.And I I never had problems with improper oil return.
I'm convinced that you don't need all this if your lines are correct sized and installed.

[guapo]

I Install Oil return to Oil reservoir. Most of my unit has oil separator sperially ammonia.

[NoNickName]

Oil can be returned in the motor flange or the compressor crankcase.

BTW. Refrigerant can be charged in the discharge valve, as soon as it's warmer than the the condensing temperature.

[chemi-cool]

The reason I wrote this post is a problem with 7 identical condensing units on a big milk tank.

The compressors involved are MT064 and the oil return connection is to the oil equalising connection.

All the pipes are leaking. I installed new 1\4 pipes connected into the inlet of the liquid separator and the problem gone.

These units do not need an oil separator and and the reason for it is lack of understanding the principle work of flooded evaporator.

Whenever an oil reservoir is present, I agree that the oil should return there.

Refrigerant charge into discharge line - When the unit is under vacuum, I've seen many engineers charge liquid refrigerant into the discharge line. The refrigerant, when reaching the oil separator behaves like oil and flow back into the crankcase and when the compressor starts, if the valves do not break, it washes the oil out of the compressor.

[jmully]

am i wrong in thinking if your charging a system thats been vacced out to charge in to the reciever until the pressures equalize then charge into ur suction whilst the plant is running?

[DEVIL]

Well as i understand u could feed it in the suction line if it's possible as far as possible from the compressor because it should be a small amounts of liquid in it, but feeding to the liquid separator might make it mix with the liquid in the separator and not get adequately back to the compressor , and u should charge directly in to the liquid receiver and that way it wouldn't get in the oil separator.
What u also could do is feed it by a capillary tube or a small dimension pipe (depending by system size)so even if liquid gets back, it should be small amounts
But mainly it's fed to the compressor oil return port (as i do)

[NoNickName]

Originally Posted by chemi-cool

Refrigerant charge into discharge line - When the unit is under vacuum, I've seen many engineers charge liquid refrigerant into the discharge line. The refrigerant, when reaching the oil separator behaves like oil and flow back into the crankcase and when the compressor starts, if the valves do not break, it washes the oil out of the compressor.

Oh, my gosh. Tell me this is a joke.

[chemi-cool]

Originally Posted by NoNickName

Oh, my gosh. Tell me this is a joke.

Next time I will see an "expert" doing it, I promise to take some pictures.....

[NoNickName]

Yeah precharge in the liquid receiver, and push it by warming the refrigerant if the compressor is running, or suck it in the suction but verrrrrrry slowly.
No use charging the liquid separator. It should be as empty as possible.

[bill1983]

Originally Posted by Peter_1

Always, not mostly to the oil reservoir on packs.
But...I never installed an oil separator in my whole life on a single evaporator/compressor application, even not on long lines or freezers.And I I never had problems with improper oil return.
I'm convinced that you don't need all this if your lines are correct sized and installed.

on single evap/condenser systems peter should be right, but many of the systems i work on are either sized, installed or set up incorrectly. this is why seperators have usually been fitted in the frst place, not as an original specification, but because the problems caused by any of the above have never been correctly identified.
in those situations, the oil return is nearly always returned directly to the sump or via a regulator of some sort.
i have never heard of liquid being charged into the discharge side of the compressor. quite often it is charged into the suction usually with dramatic results if allowed to enter the compressor at a higher rate than it can "flash off" at.

[DEVIL]

Originally Posted by bill1983

i have never heard of liquid being charged into the discharge side of the compressor. quite often it is charged into the suction usually with dramatic results if allowed to enter the compressor at a higher rate than it can "flash off" at.

No one says that charging in the suction line is fool safe on the contrary , but i see it as the best way of charging (after you charged the liquid receiver ), if u are paying enough attention you can do it as safe as it gets (my way and never had a problem)

Or another safe way is how one of my engineer is doing it, u charge the liquid receiver then start the system , u do a pump down, and charge again

[Emmett]

(1) I have always seen seperator oil return line piped to the compressor sump and
(2) Why are you charging liquid through the discharge side? How do you overcome the discharge pressure?

[old gas bottle]

it,s all begining to sound a bit messy to me,why not just charge most of the estimated charge streight into the reciever not the discharge port,after all thats where it belongs ! then carefully top it up through the suction while its running as far as connecting the oil sep return pipe to the suction anywhere [did i read it right ?]well what hapens when the float opens and a litre or two of hot high pressure oil enters the inlet side of the compressor or even the accumilator,it does not belong there either. streight back to the crankcase via a soniliod valve enigized only when the compressor runs,nothing wrong with the traditional way.

[NoNickName]

Yeah, KISS.

[john.sikiotis]

ok what you saw is that the technician had CLOSED the reciever valve that goes to the filter and then to the rest circuit.He charged from the filter or something like that and the refrigerant was doing the circle and end up in the reciever. Ok? Not the right way if you don't know what you are doing!!!!. The right way is to charge from suction line before the accumulator .

[DEVIL]

Originally Posted by john.sikiotis

ok what you saw is that the technician had CLOSED the reciever valve that goes to the filter and then to the rest circuit.He charged from the filter or something like that and the refrigerant was doing the circle and end up in the reciever. Ok? Not the right way if you don't know what you are doing!!!!. The right way is to charge from suction line before the accumulator .

Yup,your right way is the way u flood a compressor with liquid !!!

Why ?

1 - a suction accumulator is not obligatory, so u might not have one
2 - suction accumulator is usually smaller then liquid receiver.

So ... what happens

The liquid you add to the accumulator is in large quantity (because u did not say u first charge in the receiver ) will at one point be flooded and liquid will go to the output going to the compressor .

The suction accumulator is not meant to store liquid that's way it's smaller , it's meant to protect the compressor from liquid .

If u have a suction accumulator then u first charge the liquid receiver and it is usually obligatory for a refrigeration system to have one , and then add to the accumulator if u have one, if not, to the suction, but in small quantities (because u already charged the large amount in the receiver)


What i was writing about my engineer was another right way, because the liquid u charge goes to the evaporator, and returns as vapor to the compressor not doing any harm to it