Poor performance provision freezer

[CHENGTRIT]

Hi there. Im new to this forum, and hope you guys can help me out with a problem.
Onboard this ship we have a provision cooling/freezing system consisting of 2 evaporators (one freezer and one in the cooling room) and two compressors sharing a common liquid line. Each compressor has its own condenser. System is running on R404
Experiencing very low performance when running compressor 2. Suction pressure barely over 0 bar Head pressure around 12 bar. Freezer Evaporator temp is only -6C. Liquid is visible in sight glass wet indicator is OK.
No problems when running compressor #1. -21C temp head pressure 15bar and suction pressure 1bar
We recently needed to remove a lot of oil from comp2 as it fills up while comp1 is loosing oil when its running.
We removed almost 2 liters. Max volume in sight glass is about 1 liter.
After we removed oil from comp 2 we can see foaming inside the crankcase. Can all this be due to a faulty reed valve?

[nike123]

Hi there. Im new to this forum, and hope you guys can help me out with a problem.
Onboard this ship we have a provision cooling/freezing system consisting of 2 evaporators (one freezer and one in the cooling room) and two compressors sharing a common liquid line. Each compressor has its own condenser. System is running on R404
Experiencing very low performance when running compressor 2. Suction pressure barely over 0 bar Head pressure around 12 bar. Freezer Evaporator temp is only -6C. Liquid is visible in sight glass wet indicator is OK.
No problems when running compressor #1. -21C temp head pressure 15bar and suction pressure 1bar
We recently needed to remove a lot of oil from comp2 as it fills up while comp1 is loosing oil when its running.
We removed almost 2 liters. Max volume in sight glass is about 1 liter.
After we removed oil from comp 2 we can see foaming inside the crankcase. Can all this be due to a faulty reed valve?


If nobody has added any oil before, you now have compressors starved with oil. Expect more compressor damage if system continue to run that way.

What is oil level regulation method in that system?
What is superheat and subcooling when compressor 2 is in operation?
What is crankcase temperature of compressor 2?
Does compressor 2 have crankcase heater and is he OK?
What is evaporator air in and air out temperature when you measuring 0 bar suction?
Does both evaporator solenoids are open when you have this low pressure?
Describe control logic of compressors and evaporators solenoids activation.

[icecube51]

are the two compressors sharing a common suction line to??

Ice

[CHENGTRIT]

Hi.

There is no oil level control of the compressors.
Only one compressor is running at any time. The compressors share a common suction line.
Both solenoids are open. When running comp1 there are no problems. Same configuration running comp2 gives low suction pressure and reduced heat exchange in both evaps.

ChengTrit

[CHENGTRIT]

Here is a schematic of the system

[nike123]

From this blurred diagram, I think you have oil separators at every compressor. Is that correct?
If you have bad read valve then suction pressure would be elevated!
You could make pump down of both compressors and compare pressure equalization time to establish are the valves are OK!
Are both compressor of same model# and one of them is as redundancy? They newer work together?

[Andy]

Hi there. Im new to this forum, and hope you guys can help me out with a problem.
Onboard this ship we have a provision cooling/freezing system consisting of 2 evaporators (one freezer and one in the cooling room) and two compressors sharing a common liquid line. Each compressor has its own condenser. System is running on R404
Experiencing very low performance when running compressor 2. Suction pressure barely over 0 bar Head pressure around 12 bar. Freezer Evaporator temp is only -6C. Liquid is visible in sight glass wet indicator is OK.
No problems when running compressor #1. -21C temp head pressure 15bar and suction pressure 1bar
We recently needed to remove a lot of oil from comp2 as it fills up while comp1 is loosing oil when its running.
We removed almost 2 liters. Max volume in sight glass is about 1 liter.
After we removed oil from comp 2 we can see foaming inside the crankcase. Can all this be due to a faulty reed valve?

Hello CHENGTRIT

low suction pressure would indicate a blockage, not damaged reed valves.
Is all the valves open full?

Would there be a drier for each condenser on the liquid line and is it ok?

Kind Regards Andy D

[CHENGTRIT]

Yes that is correct.

chengtrit

[CHENGTRIT]

No,there is only one common drier for both condensers.

chengtrit

[nike123]

Yes that is correct.

chengtrit

Check pressure drop between compressor 1 and 2 discharge and at port before filter and compare both circuit.


http://farm4.static.flickr.com/3022/2935404841_61118cf9f9_o_d.jpg

[CHENGTRIT]

The highlighted valve is a non-return valve.

[Gary]

We recently needed to remove a lot of oil from comp2 as it fills up while comp1 is loosing oil when its running.


This isn't clear.

Are you saying that comp2 fills with oil and comp1 empties when comp1 is running?

Or are you saying that comp2 fills and comp1 empties when comp2 is running?

[CHENGTRIT]

This isn't clear.

Are you saying that comp2 fills with oil and comp1 empties when comp1 is running?

Or are you saying that comp2 fills and comp1 empties when comp2 is running?

Comp 2 fills and comp 1 empties when comp1 is running

[Gary]

Comp 2 fills and comp 1 empties when comp1 is running

I'm looking at the diagram and trying to figure out how this is possible.

[nike123]

The highlighted valve is a non-return valve.

That symbol doesn't look like symbol on other circuit! It has something attached to it! What is that?

[nike123]

I'm looking at the diagram and trying to figure out how this is possible.

Maybe if oil return line from oil separator of comp.1 is blocked or oil float is jammed or oil filter is blocked! Oil then circulate and goes to common suction line and fills both compressors, but oil level is not equalized with missing oil equalization line.

[nike123]

Ignore.....

[Gary]

Or possibly the oil return line from separator1 is hooked up to comp2?

[Gary]

Or maybe some sort of oil equalization system has been added that is not on the diagram?

[Gary]

Looking at the diagram: When one compressor is running, what stops refrigerant from gathering in, and staying in, the inactive condenser?

It seems to me that when using one system, the inactive system should be completely isolated by closing the hand valves before the compressor and after the condenser.

You might try running each system with the opposite system manually isolated to see if this improves the performance.

[icecube51]

i think there is a valve not closing properly.or staying open.if you are working whit one line,there has to be a by-pass or a regulator to prevent things like that to happen??? or am i wrong ??
something is not wright in the drawing....
Ice

[Gary]

After each condenser, there are two manual valves in series (?). It seems like one of these should be a check valve?

[nike123]

After each condenser, there are two manual valves in series (?). It seems like one of these should be a check valve?
By look of the symbol, it seems that valve after condenser is some kind of reduction valve. His left side is smaller than right side.

If we could get clear schematic and symbol legend, than some things should be clearer.

[Andy]

Gents,
it is quite normal for oil to migrate to the off compressor where this type of common suction line is employed.

I have even seen the oil migrate from the discharge lines, where a worn check valve was fitted.

Kind Regards Andy

[CHENGTRIT]

Thank you guys for all input regarding this problem.
We will keep the standby compressor and condenser isolated and observe the oil levels in each crankcase.
After 24 hrs running it seems OK so far.


ChengTrit