Hall Screw 2020 erratic noise when unloaded

[JP85]

hi, Hall Screw 2020 running on Ammonia when this compressor is unloaded to 10% there is a high pitch noise coming from compressor. I have been told this is due to compressor being unloaded to far, causing unload block to rub on casing causing this issue.Any ideas?

[RANGER1]

JP85,
Can you give us a bit more information like suction, discharge, oil pressures & temperatures.
Also type of oil cooling, like water cooled or liquid injection cooling.
Does the machine seem to perform when running, or can't run long enough to find out?
How many hours on machine since last inspection, usually inspect star wheels annually as it's very easy.

The oil level scenario is interesting as symptoms usually the other way when 100% loaded

[JP85]

Suction Pressure 50Kpa
Discharge 1050Kpa
Oil Pressure 950Kpa
Oil Is water cooled
Run hours says 5000 hours, but believe this may be untrue as hour meter may have been replaced as some stage. Unsure on last inspection, have only recently started to look after this site.
Compressor runs fine apart from oil issue at this stage. Has never really given problems in past, only high pitched noise when unloaded. We are currently trying to advise customer of stars needing to be inspected as unsure of last inspection.

[RANGER1]

JP85,
Discharge & oil temperature would be good as well if possible.
The conditions you supplied can in some compressors cause issues, as there may be no gas flow through compressor due to the differential between suction & discharge pressure & unloaded operation.
Oil can build up in machine & sounds like nuts & bolts going through it.

A a simple check of star wheels is very easy requiring side plate gaskets, if they get damaged.
Condition of star wheels can be checked, clearances & worn thrust bearings on star wheel shaft.
This check eliminates a lot of things.
Also does this system have a economizer as well & is it's operation ok, no flood backs or anything out of the ordinary.

[gerry79]

Hi Ranger

I'm also involved with JP85 in dealing with this problem. To answer your questions above, conditions are:


Discharge temp 70*c
Oil Temp 45*c
Sub-cooling type Economizer is installed by never used due to flood back issues


Interesting to hear your comments about oil accumulation in the Compressor, we have had numerous low oil level trips from the separator level sensor (WEKA type, Yes heat trace is working!). When we arrive on-site the separator oil level is fine, it doesn't appear to be throwing oil out of the skid! We maybe seeing oil migration within the skid?

I'm in the process of drafting a covering letter to the customer recommending the clearance checks you've alluded to, I've only been able to find J&E Halls 25,000 hr inspection specification to support our recommendation, can suggest any other sources of reference?

Thanks for your Help!

[RANGER1]

Hi Ranger

I'm also involved with JP85 in dealing with this problem. To answer your questions above, conditions are:


Discharge temp 70*c
Oil Temp 45*c
Sub-cooling type Economizer is installed by never used due to flood back issues


Interesting to hear your comments about oil accumulation in the Compressor, we have had numerous low oil level trips from the separator level sensor (WEKA type, Yes heat trace is working!). When we arrive on-site the separator oil level is fine, it doesn't appear to be throwing oil out of the skid! We maybe seeing oil migration within the skid?

I'm in the process of drafting a covering letter to the customer recommending the clearance checks you've alluded to, I've only been able to find J&E Halls 25,000 hr inspection specification to support our recommendation, can suggest any other sources of reference?

Thanks for your Help!

Without Hall manual at hand I can compare different brand of compressor vilter mon screw.
See pages 50-51, as they suggest annual inspection of star wheels & bearing play.
It's so easy to check on Vilter & Hall, just a few gaskets.
In the meantime I will check in manual when possible.

http://www.emersonclimate.com/europe/Documents/Brands/Vilter/Product%20Manuals/Brands_Vilter_Manual_VSM%20VSS%20Compressor.pdf

[Magoo]

Definitely sounds like star wheels are out of spec.,
Interesting that economizer is isloated, and that system sits at minimum load and not stopping, low gas and oil flow through compressor will agrivate situation. Is economizer an open or closed flash type?. Not using econo will seriously derate system effciency.
Is this a Fonterra site?.

[RANGER1]

Another possibility could be on older units an external drain was installed.
It is a line between compressor suction chamber where star wheels are draining into oil separator.
In this line could be a Danfoss NRVA check valve with Spring removed.
On newer ones it's internal using a ball bearing & circlip.
When compressor running check valves closed, when off gravity allows non return valves to open draining any oil build up on failed start ups etc.
If non returns not closing could get oil from separator migrating into suction chamber as well as internal bypass reducing compressor efficiency & capacity.

[RANGER1]

14173

This page from manual confirms every 25000hrs as you said.
If something is concerning you recommend inspection in writing, as it does not take a lot of time.
If nothing wrong, great news, if something is wrong, maybe prevent damage or a least prevent anymore.
If client needs more convincing, give it time I guess.
I would agree more with Vilter recommendation.