Oil Loss 250 VLD Mycom Screw

[Keith1977]

I have been experiencing major oil loss in our low stage 250vld Mycom screw compressor.
The problem became expensive 2 years ago.
At first the losses were minimal having to add oil once a week.
2 years ago I changed out the coalescers with frick coalescers not realizing the error I had made. Oil loss was crazy. I changed back to the proper Mycom coalescers and the problem continued.
I have spoken with Mycom about the problem periodically and really have made no progress.
The suction check valve was changed and oil loss to the low side was eliminated. Half the battle was won as we were still losing out of the discharge to the intermediate side.
I noticed that at some point the liquid drainer on the coalescer section of the seperator (oil return to suction of compressor) was removed. I tried installing one with results. The coalescer glass was showing an oil level (I know not a good thing) but I was loosing less oil (Approx 5 gal per day)
Ideas are running out.
If the load is removed from the compressor as soon as it starts unloading it will cutout on low oil pressure. When this happens before the compressor can be started the slide valve must be unloaded. During this process we need to add 5 to 10 gallons of oil to keep the pump pressure up and unload the slide valve.
By the way it is a full time oil pump and oil temperature is where it should be.
Mycom keeps thinking that the oil seperator is undersized which it is but I beleive another problem is there as why would the problem get worse.

We have also tried an anti-foaming agent with no success.

Could this be a clearance issue?
Could this be a bad seal on the slide valve piston?
Does anyone have any other suggestion?

Thanks for reading sorry to carry on but I wanted to give as much info as possible.

[keepitcool]

Mycom is probably right. Was this originally designed as a booster or a high stage machine that was converted? Small separator and high velocity means oil bypass.

[Keith1977]

I do beleive the seperator is undersized.
But this does not explain an increased oil loss in the machine.
It has always been a booster to my knowledge. I have been operating this compressor for 5 years now.
If I can get the capital the seperator will be sized accordingly.
I can't help but wonder why things got worse?
I hate not being able to find a solution.
I have even tried increasing the C.C. on the high stage compressor to reduce velocity. This had no impact.

[Iceehot]

file:///C:/DOCUME%7E1/MICKEL%7E1/LOCALS%7E1/Temp/moz-screenshot-3.jpgfile:///C:/DOCUME%7E1/MICKEL%7E1/LOCALS%7E1/Temp/moz-screenshot-4.jpgThe coalescer glass was showing an oil level (I know not a good thing) but I was loosing less oil.
What type of oil return did you install?
Are you still seeing oil in coalescer glass after installing?
My older packages have an auto float trap for return, newer packages have a hand adjustable needle valve with small sight glass to see oil return. If I see oil in coalescer glass, open needle valve more. Both types have fine filter screen that can occasionally plug up.
Years ago I had a Suction check installed upside down, lost lots of oil when it was unloaded.
Whomever made the package should be able to tell you if it was designed for Booster or hi-stage.
Could this be a bad seal on the slide valve piston? No, bad seal on slide valve will cause it to not load or unload properly.
Oil injection: is it adjustable? be careful adjusting to not go too little.

[RANGER1]

Keith1977 ,
It would be helpful to know if
oil seperator is horizontal or vertical ?
number of coalescers plus dimentions
Also have they been rechecked for security and condition. Horizontal filters can slip and not seal on ends if not tight enough.
If oil seperator was designed for booster it should be bigger than high side duty seperator.
What oil,discharge temp is it when running ?
Also check

[keepitcool]

You said you fixed the suction check valve. Did it spin backward when it was shut down before you did this? I assume that it does not now. That only leaves one way out. Check what RANGER1 suggested about the security of the filters. It may have blown an O-ring on one of them. But if this is the case you usually loose the whole charge pretty fast.

[Keith1977]

Here is the information you guys have requested.
It is a horizontal seperator. Height 8' Diameter 24".
It is a Mycom compressor but the package was put together by another company.
It has been a low stage machine since install.
The oil injection is not adjustable.
I first installed a float drainer with a 5/16" port but this did not give me enough flow. I then changed to an expansion valve with a 3/8" port. Adjusted just enough to keep the sight glass empty.
There is 2 coalescers Height 36" x 9.5" Diameter.
Oil discharge temp is running between 131 and 137 DegF.
I have not checked the coalescer seals and will schedule to have this done.

Hope I've covered everything.
Thanks for the advice.

[nh3wizard]

Is there a side port / economizer? If the check is bad I have seen oil loss this way.

[Keith1977]

Correction it is a vertical seperator.
Sorry to early in the AM.

[keepitcool]

Did Mycon say why they thought the separator was too small? Who designed and assembled the package? was it brand new when it was installed? It may have been a booster from day 1 at your plant but in another life it may have been designed as a high stage machine.

[Keith1977]

Mycom said it was undersized due to size and calculation I beleive.
There is no economizer port.
The package was put together new by Cimco in 1987. The compressors were replaced again approx 7 or 8 years ago. I beleive they were replaced due to the screws being worn badly and the output was reduced significantly.

[keepitcool]

Compressors plural?

[Keith1977]

Yes both compressors.
The 250 VLD
and the high stage 200 VLD

[expat]

Sorry for butting in, as this stuff sounds out of my league. But, is it a silly question to ask where all this oil is dissapearing to?

[Segei]

Assume that oil separator undersized. Try to run this compressor on manual slightly unloaded(80-90%) and second compressor on auto. It should help if oil separator size is real issue.

[Iceehot]

[quote=RANGER1;119251]Keith1977 ,
Horizontal filters can slip and not seal on ends if not tight enough.
Agree: I have an older Vertical separator with Vertical coalescers, a ring o one end to hold them and Gasket in place. If it isn't exact they leak bad. Also they have a vertical dip tube down into the center of coalescer to return oil to suction. These can plug, kink, or not return if connection to tubing isn't tight. These aren't standard coalescers I'm used to seeing on newer packages, they are solid on one end and flow is from outside to in, so dip tube to center returns oil.

[RANGER1]

For booster application this seperator is definately to small.
For 250VLD you would require 6 off 36" x 9" coalescers with vessel dia of 36".
It doesnt stand a chance.

[Keith1977]

Has anyone tried using the Frick convoluted coalescers? From what I understand they are meant to reduce oil loss in undersized seperators.
At the price of $800 a piece I thought it would be worth hearing some testiment.

Thanks

[Keith1977]

All oil ends up in the Intercooler.

[RANGER1]

The extra surface area of the frick filters at a guess maybe 30-40 % ,which would help . But even if they do it still is only equivilent to 2.5-3 coalescers in total.
From my sources it is only half number required , so oil carry over is expected.

[keepitcool]

Remember Kieth. You said that you tried something like this two years ago. The coalesces are not the problem. Your problem is either the machine is not being used for what it was designed to do or the design is flawed. Vessels are not that expensive in relative terms. Having a vertical separator is a huge advantage in this situation. I would say get the new separator in the budget and fix it once and for all.

[Josip]

Hi, Keith 1977 :)


I have been experiencing major oil loss in our low stage 250vld Mycom screw compressor.......


We have also tried an anti-foaming agent with no success.......



.... seem you have a lot of saturated/wet (can you check suction superheat... ..?K) refrigerant coming back..
....carrying your oil out ..... otherwise no oil foaming... I think .... too small oil separator, ..... is the place where your problem started .... there must be a leak

... maybe .... broken gaskets under coalescers filters, damaged coalescers filters, or some problem with baffle plate (we had similar problem, many years ago) - it was not welded good all around and lot of oil runaway, more and more as time passed ... was not easy to determine that problem... changed oil separator and problem solved;)

Best regards, Josip :)

[Magoo]

The critical point was that the machine lost oil and oil pressure when unloading, the o/ring seal on the shaft at the point between the unload chamber and the discharge, is stuffed.
Talk to Mycom and get the correct o/ring compound, and service kit.
Similar problem years ago with a machine on R-22 and wrong o/ring material compound.

magoo

[RANGER1]

The oil pressure problem when unloading could be jammed oil pressure regulator , worn oil pump , oil filter blocked needs changing (high pressure drop across filter so when loads oil pressure dips ) .Also main bearing plus balance piston / sleeve could be worn causing more oil flow than oil pump can deliver . Check simplest things first.
The only options apart from replace seperator would be check if filters are secure and OK and no tears in filter .
Test run , if no good replace filters with larger surface area or more pleats.Filters must be tightened resonably firm
Discharge temp looks OK not to cold.Assume oil injection line has orifice.
Oil level in seperator should be kept to to a lower limit to see if it makes much difference.
Oil return line should only return droplets , if any more something is loose or dislodged on coalescers.