Flushing oil from a system.

[djbe]

Can anyone tell me the best way to flush excess oil out of a system?

We are looking at a chiller (Prestcold MALGW500 & Searle K180) that has lost a new compressor to oil slugging.

We suspect the oil seperator has not been working properly and are going to replace it but we want to get any oil out of the rest of the system.

Thanks,djbe

[Andy]

Can anyone tell me the best way to flush excess oil out of a system?

We are looking at a chiller (Prestcold MALGW500 & Searle K180) that has lost a new compressor to oil slugging.

We suspect the oil seperator has not been working properly and are going to replace it but we want to get any oil out of the rest of the system.

Thanks,djbe

Most chillers don't have oil separators.If it's a Searle KM180 you are talking about it is a chill or deep freeze room we are discussing

Oil separators are not strictly need in any properly designed ***** system. So saying that the problem lies in the part load oil return performance of the refrigeration system.

Kind Regards Andy

[djbe]

Hi Andy,

It's a chill room but this plant looks like it was fitted second hand many years ago. (Basically because the condensing unit has an identification plate relating to a dairy chill room not relating to the site in question)
The prestcold condensing unit is fitted with an AC & R oil seperator.

There is a bit more of a story to this:

The condenser coil has been ropey for years but the customer has always insisted it will be O.K. despite never achieving desired temperature.
We recently persuaded them to change the coil and the unit immediately started to perform.
After approx. 2 weeks the compressor valve reeds failed taking the compressor pistons and bores with them. It looked like the compressor (PLG500/0074) was the original so we just put it down to old age.
We fitted a reman. compressor and this lasted 1 week before breaking a rod. During the time up until the failure the unit ran perfectly, smooth with no signs of impending failure.
After stripdown the compressor firm advised that there was a lot of oil on top of the pistons (hence suspected oil slugging) the oil level in the sump was good between 1/4 & 1/2 sight glass.

Is it just coincidence that these problems have occured since we replaced the condenser coil?

[bill1983]

hi djbe
hrp sell a chemical cleaner that can be pumped around the system which dilutes and carries the oil and any contaminants with it. i've only ever used it on small systems, window rattlers and service cabinets when i have disconnected the comp and used an oil pump to flush a couple of litres around and into a bucket, to collect the waste before a thorough flush with nitrogen to clear the remainder. you then reconnect the compressor before pulling a good vacuum etc.
the question is, do you need to go to these lengths, is the system oil contaminated? will the oil return with the refrigerant once you have replaced the comp and sep ie what is the pipe run like, oil traps, fall to cond unit
other things to consider, is the oil flow from the sep stopped by a solenoid when the system shuts down? is the seperator the correct size? not physically but duty wise is the problem with the oil sep or is there another problem which could give you the same symptoms ie oil in the head and broken con rod. maybe the tev size or setting need looking at before you restart.

[djbe]

Hi Bill,

I've seen the cleaner at HRP called Endoflush but have no experience of it. Does the flush through with nitrogen clear it out O.K?

The pipe run isn't bad but there is no fall to the cond. unit.
The seperator oil return doesn't go through a solenoid, just straight into the compressor crankcase.

We will check the TEV and oil seperator size but getting the oil out is more belt & braces than anything just to ensure that we are starting from square one when we reinstall the compressor.

thanks,djbe

[old gas bottle]

most of the oil will be sat in the evaporator and commong back in a big gulp hence hammering the top end of the comp, sounds like drastic measures time,i would pump down, remove the tev phial from the suction pipe, open the liquid line at the valve,dril a 1/4 hole in the suction pipe at the lowest and accessable point,drian the crap out,braze the hole up,refit it all back,vac the line out,change of drier and run it,let the system settle for 24 hr before adding or removing any oil, i would alsogive it a belly full of quality semi of fully synthetic oil to boot, just thought,its not been icing up and slugging liquid has it !! cheers.

[Andy]

Hi Andy,

It's a chill room but this plant looks like it was fitted second hand many years ago. (Basically because the condensing unit has an identification plate relating to a dairy chill room not relating to the site in question)
The prestcold condensing unit is fitted with an AC & R oil seperator.

There is a bit more of a story to this:

The condenser coil has been ropey for years but the customer has always insisted it will be O.K. despite never achieving desired temperature.
We recently persuaded them to change the coil and the unit immediately started to perform.
After approx. 2 weeks the compressor valve reeds failed taking the compressor pistons and bores with them. It looked like the compressor (PLG500/0074) was the original so we just put it down to old age.
We fitted a reman. compressor and this lasted 1 week before breaking a rod. During the time up until the failure the unit ran perfectly, smooth with no signs of impending failure.
After stripdown the compressor firm advised that there was a lot of oil on top of the pistons (hence suspected oil slugging) the oil level in the sump was good between 1/4 & 1/2 sight glass.

Is it just coincidence that these problems have occured since we replaced the condenser coil?

can you check out the pipe sizing on this job.

By changing the condenser you have increased the refrigerant flow through the system (the system has way more capacity)
This could have tipped the pipe sizing over the edge, with massive velocities in the suction line, carring back oil that has lay there for years.

Cure would be a new suction line

But what old gas bottle suggests will help, basically drain the old oil charge from the low side and start again.

You could add a suction trap to catch the oil (a suction accumulator with the oil return inside removed)

and drain the oil comming back, removing this when the oil starts dropping in the sump.

Kind Regards Andy

[old gas bottle]

with all respect to andys suggestion i cant see the new condenser coil causing the problem and changing the suction line would help either,if the old condenser was knackered the head pressure and suction would have both been higher than required,hence to gas would have been traveling arround the system faster,i think you did right by changing the oil sep as theese are a good thing on semis even if they are not realy needed, cant remember if that model has the suction valve on the head or end plate, theres no reason why if the old oil out of the evap is drianed off and theres a rebuilt compressor on the job,new oil sep and oil,pressure switches set right,[dont let it drop in a vac on pump down]that it should not settle down,run it through a defrost asswell ,check the termination temerature and drip down time/fan delay no to short or long. good luck,

[Andy]

with all respect to andys suggestion i cant see the new condenser coil causing the problem and changing the suction line would help either,if the old condenser was knackered the head pressure and suction would have both been higher than required,hence to gas would have been traveling arround the system faster,i think you did right by changing the oil sep as theese are a good thing on semis even if they are not realy needed, cant remember if that model has the suction valve on the head or end plate, theres no reason why if the old oil out of the evap is drianed off and theres a rebuilt compressor on the job,new oil sep and oil,pressure switches set right,[dont let it drop in a vac on pump down]that it should not settle down,run it through a defrost asswell ,check the termination temerature and drip down time/fan delay no to short or long. good luck,

Why not check out the pipe sizes to prove me wrong

An undersized condenser will seriously reduce the capacity of a compressor.

If the liquid quality entering the evaporator is poor, the back pressure will be lower than that with a proper condenser

If I am wrong guys prove to me I am wrong

Try plotting the old and the new cycle on a PH diagram (or use cool pack)

Maybe there is a record of the old and new pressures

Kind Regards Andy

[old gas bottle]

andy i,am not having a go matey, iam assuming the condenser was just an old for new ,putting it back to standard,from what the chaps say it then improved meaning to me that the condensing temperature droped to a normal level ,i,ve had this many times over the years and found it to be bad maintainece,never having a oil change etc,the old mineral oil thickening up and laying everywhere bar in the sump,if alls well at the unit end now i still think its the evaporator end causing the problem. i may be wrong,have been loads of times !!

[djbe]

Hi Andy & Old Gas Bottle,

I think there is a lot of merit in the suggestions that both of you have given.

We are going back to the site early next week and will follow them up.

A bigger problem at the moment is that the remanufacturer is telling me that they are having difficulty in locating the spares to rebuild the compressor again??????

I'll let you know how we get on and in the meantime thanks for the help guy's.

Regards,
djbe.

[old gas bottle]

i would not have it rebuilt again anyways chap,just use it as a exchange unit, j,e hall will have them on the shelf or zeftec are nearer you,andy and myself are killing the gray matter trying to think of the causes when it might just have been a bad compressor, i got sick of them last year failing with silly things so i try and fit new where i can,saying there was oil causing the problem can also be a good cop out, if a rod or valve plate fail they chuck oil out anyway,hope it all goes well.