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Thread: Oil systems
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31-03-2005, 07:56 PM #1
Oil systems
Hi All
Could someone explain to me how the oil seperation process would be affected on a pack if
1.The pack was low on gas
2.The pack was greatly overcharged with oil
I am thinking that on both occasions the oil would flow to the evaporator.
Many thanks Bernard
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31-03-2005, 09:29 PM #2
Re: Oil systems
Originally Posted by bernard
Gas shortage can reduce oil return.
Oil overcharge can cause oil carry over and or poor compressor oil return.
Kind regards.MarkLast edited by Mark; 11-04-2005 at 10:17 PM.
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31-03-2005, 09:35 PM #3
Re: Oil systems
I am thinking that on both occasions the oil would flow to the evaporator.
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31-03-2005, 10:31 PM #4
Re: Oil systems
Bernard.hi must get some sleep .I will continue this tommorow.
zzzzzzzzz
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01-04-2005, 09:30 PM #5
Re: Oil systems
Hi Bernard
If the pack was low on gas I doubt the oil would be affected greatly . I mean yes the flow coming back from the evap would be slightly less but the oil should have been seporated before the evap anyway.
If the pack was really low on gas it should have shut down before any problems arrise.
Being overcharged with oil would only cause it to dumped straight into the suction pipe through the gas releaf valve. ( knacking the comp)IF AT FIRST YOU DON`T SUCCEED.
DESTROY ALL EVIDENCE THAT YOU TRIED!
and go get a cuppa
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02-04-2005, 07:41 PM #6
Re: Oil systems
A scroll pack using a pulsed oil managment system with a high pressure separator/resevoir,overcharge may cause carryover.
Another pack with resevoir overcharge of oil may bleed back through the suction header via pressure valve.
Low gas charge may cause case alarms.
Low gas charge may cause pack alarms.
Low gas may not cause either of the alarms.
Reduced gas charge may cause compressor cycling,hunting leading to a reduction in impingement through the separator.And consequential oil starvation may occur.
Low gas charge on a high pressure oil separator may disperse the oil around the system.
Coalescent separators are 99.9% efficient.
Float operated impingement separators are 99% efficient.
Sometimes they are not.
Coalescent separators are not velocity dependant.
Float operated separators are not velocity dependant.
Sometimes they are.
Floating the head pressure may effect compressor oil return.
It may not.
Best regards.Mark
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03-04-2005, 08:41 AM #7
Re: Oil systems
Originally Posted by chillin out
This was the time when packs were not so common to install and you had to make them yourselves.
The packs were even made in a special way according a 'mathematical' row, well... at least ... some sort of it.
A 0.5 HP, HP, 2HP, 4 HP, 7.5 HP (8 doesn't exist) and 2 pieces 15 HP.
The PLC then measured the LP. As long as LP was too high, the PLC switched to the next higher step (with delay times between it of course) We could regulate in steps of 0,5 HP.
If pressure became too low, then we switched too the next lower step, again delay times and in steps op 0.5 HP.
So there was no oil separator nor oil floats on the compressor.
All these packs are still running with the original compressors.
We even made a pack with Copeland machines and a 10 HP Bock machine between it. This machine was then relative new (+/- 5 years) and client asked us if it was possible to use this machine. Also this Bock (now 15 years old) is still running.
So, oil return is for me more proper tubing techniques, suction inclined to the compressors, speeds in the tubing calculated like it has to be done, a very well designed suction header,...
We also still use following technique to ensure oil return (just in case of...) switching all the SV's open twice a day during the night for 15 minutes so that all the tubes encounter a maximum gas flow. The main header was calculated at 75% of the full capacity so that speed was high enough.
If the pack was really low on gas it should have shut down before any problems arise
Being overcharged with oil would only cause it to dumped straight into the suction pipe through the gas relief valve. ( knacking the comp)
And why should if come back sudden if lines are properly installed?
What do you mean with the gas relieve valve?Last edited by Peter_1; 03-04-2005 at 10:03 AM.
It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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04-04-2005, 06:55 PM #8
Re: Oil systems
Hi
If a pack was controlling say 6 cabinets and one was badly iced or had problems with the eev,then It would flood back lowering suction pressure therefore staging down the compressors causing all the other cases to go high temp.Is there away to stop this.
thanks bernard
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04-04-2005, 07:38 PM #9
Re: Oil systems
OK, 6 cabinets on a pack and one iced. It will flood back -perhaps- if the EEV didn't prevented it.
But.... the LP will not drop at all, the pack controller will maintain a stable suction pressure.
The only thing that will happen is that the pack perhaps will switch to a lower capacity step. If it's a frequency controlled compressor, speed will be slightly decreased. That's all.
So the LP on the other will remain the same.
Of course, mass flow will decrease in the main suction line and the suction header.
Same story if you lost gas: LP will remain the same but with fewer compressors.It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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04-04-2005, 07:41 PM #10
Re: Oil systems
Originally Posted by bernard
On a suitably designed system one case iced up out of ? should not effect the pack.
On a smaller scale an iced up coil may cause reduction in load .The valve would either momentarily shutdown completely or at a reduction in pulsed opening.Leading to HT in case/cr.
What do you mean by floodback Liquid?.Last edited by Mark; 18-04-2005 at 09:33 PM.
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04-04-2005, 08:02 PM #11
Re: Oil systems
I had a pack problem recently,4 scroll compressors,one would only run then pack would shut down,4 out of 5 cases high temp,suctions on pack badly frosted,switched off the good case frosting gone and all other cases returned to temp with compressors staging properly,case that was switched off-found set point set to low running with a/off at -7c on h/t case,adjust set point and all was well.On arrival hp was 150psi, lp would reach 40psi then pack shut down,r404a.Its on a Tescos site with one of they controllers thats controlled from America.I thought it was due to the frosting??
BernardLast edited by bernard; 04-04-2005 at 09:21 PM.
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04-04-2005, 08:15 PM #12
Re: Oil systems
Do tescos use jtl??
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04-04-2005, 08:19 PM #13
Re: Oil systems
Hi mark
Micro cool on cabinets woodely front end but are changing to eigsten,they are changing all there pack controllers at mo
bernard
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04-04-2005, 09:13 PM #14
Re: Oil systems
Originally Posted by bernard
What was your SH?
Problem can't be caused by frosting of the line?
Why frosted the line? Iced up? Bad TEV?
There must be another explanation.
Set point 7°F or 7°C?It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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04-04-2005, 09:35 PM #15
Re: Oil systems
Hi Peter
Maybe I,m missing something here but I,m always eager to learn.I took the problem to be that the cabinet was trying to achieve a temp that it was never going to reach therefore icing up causing floodback lowering the suction pressure,how low I don,t Know as the pack would shut down below 40 psi. I measured the a/off at -7 c.By adjusting the controller to the same setpoint as the rest of the cases and de-icing.The problem was gone which led me to ask the question,there is no problem now.However maybe my theory is wrong .
Bernard
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04-04-2005, 10:04 PM #16
Re: Oil systems
One controller set point deviation would not cause 4 or 5 cases to go H/T .
All cases EEV?
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