Oil retrieval

[Kevin Yeo]

May i ask wat is the best & fastest way to re-collect all oil from evaporators and pipe line, assuming a system of 4 piston compressors?

Previous service technicians pumped in oil whenever he saw low oil level in oil receiver. Too much oil in the system now.

TEV not jammed, orifice is clean. Liquid drier and suction core all ok.

Rgds,
Kevin

[Sir Josiah Sodd]

Generally oil logs in the system due to being unable to be drawn back to the compressor.
To a greater or lesser extent oil will always migrate – you can’t avoid it.

The trick of getting it back is to use the velocity of the return suction gases – that’s all. You do this by:

1. keeping the charge quantity correct, low charge is also low velocity in the suction.
2. Keeping the system resistance as low as possible – short pipe work and as few fittings as you can get away with.
3. Don’t oversize your suction pipes, especially on verticals.
4. Look at the height and diameter of vertical risers, particularly suction pipes. Running at low load conditions the oil will not entrain and lift up a high riser.
5. Don’t let the unit run at reduced load for long periods or to short cycle. This will ensure that oil is lost and doesn’t get the chance to return.

You can get oil back by simply ensuring a high load condition and running the machine. If the suction velocity is enough it will come back. If there is a sight glass in the sump you will see it. If there's too much you will need to decant it. DON'T REUSE POE.

You did not mention if this thing unloads – does it? If it does, does it get sufficient loading?

Next, unless it is a one-off problem, you need to address the question of why it is not returning. And put that right.

[Peter_1]

If the oil is in the evaporators: if you can set the evaporators in defrost mode with electrical heaters, do this for a longer then normal time.
The oil will heat up and the increased velocity after a defrost will bring it back.

If oil separators are fitted, drain some oil of the oil receiver.

If the oil is diluted in the liquid: pump all the liquid in an empty cylinder. Then let the compressor run again but fill the system only with the vaporising gas out of the cylinder and no liquid at all. Only the gas will vaporise and the oil will remain in the cylinder. Empty afterwards the oil out of the cylinder.

Then vacuum the whole cylinder for quite a long time so that moisture in the cylinder is removed. Warm eventually the cylinder with an electric heating gun. Then I should re-use the oil because it is very expensive oil.

[Johnny Rod]

Presumably they are DX evaporators not a pumped liquid system (low side header)?

[Kevin Yeo]

Yup, DX evaporators. This problem is cumulated problem and not system design problem.

Guess when the oil separator had problem, the technician wasn't aware and thought that oil level was insufficient hence he kept on topping it up.

Now with the problematic oil separator, oil doesn't go to oil receiver, instead it goes to showcase

[Peter_1]

Presumably they are DX evaporators not a pumped liquid system (low side header)?

You can remove the oil out of the liquid in either a DX or a pump system the way I described. We once did it in a cilinder of 60 kg and there was more than 5 l oil in the cilinder afterwards.

[chemi-cool]

Had once a problem of oil staying in the evaporator.

Brazed a schreder valve at the lowest point and took it out manually till I fixed an oil separator in the discharge line.

Another old and good method is to add a small amount of R 12.
Does wonders with the oil return.

Chemi

[Gary]

What refrigerant is in the system? What type of oil?

[Kevin Yeo]

R22 and Suniso 3GS. thanks

[Sir Josiah Sodd]

R22 and Suniso 3GS. thanks

....sounds like a Carrier chiller?

[Kevin Yeo]

Nope its not a carrier chiller. It a multiset consists of 4 Bitzer recip compressors.

Just curious, wat relates to a carrier chiller here??

[coolhandluke]

If you have large vertical pipe runs have they been fitted with P traps so the oil can return up the riser?

[malik55]

If possible pump down the system several times then run it and remove the exsessive oil, repeat it again if required. You must find out why the oil not comes back and have to solve it.

[Peter_1]

Kevin, what's the progress so far?

[chilly]

How do you know there is too much oil in the system?
Also i would prove the oil seperator works before doing much else.
How old is the system, does it have a history of oild return problems.

you may find the seperator has been failing for some time and this is why alot of oil is sitting in the evaporators, Get the oilsep working and you should get the oil back naturaly, you should then be able to remove access oil directly out of the oil reciever as and when it starts to over fill. If this is the problem be prepared to monitor the oil level for a long time.

The age of the system should tell us wether it is a pipework design problem or a device failure.
Hope that helps abit.

[Kevin Yeo]

The system is about 7 years old.

we examined the system, there is actually 2 problems..faulty oil separator and excess oil in the system. The previous contractor did not realise the oil sep has problem and hence topping up oil.

we connect a 6 mm pipe from liquid receiver to oil reservoir to retrieve the excess oil. The oil sep float is then cleaned.

Thanks for all your advises...