Sabroe 202LF noise

[Superfridge]

Hey all,
Sabroe 202LF, -30/+30degC, Ammonia, 3000rpm, manual fixed VI has a strange rattle emanating from the suction intake area on the compressor body and a strong side to side vibration. We have had the compressor on the ground and checked the suction check valve which has some wear but not excessive and also removed and checked the POV assembly which also appeared in reasonable order. This compressor runs part loaded, 30-40%. Is it possible for discharge gas to be redirected back into the suction intake area and overcome the suction check valve causing it to chatter? Say if the rotors were not sealing? The suction pressure transmitter is upstream from the suction check valve and reads stable, all other temperatures and pressures are normal. The compressor shaft turns freely by hand. The oil pump is prelube only. The compressor was re-aligned when re-installed. The coupling was checked and is fine. Thoughts?

[RANGER1]

Superfridge,
Single stage part loaded probably very low gas flow through compressor, if any.
If loaded more does it sound better?

[Superfridge]

No the compressor cannot be loaded any further, it’s a stand alone compressor and the load is what it is.

[RANGER1]

Has it always operated like this & something changed recently.
What is Vi set to out of interest, as thought it can be adjusted.
Can you turn economiser off & see what happens

[AKI]

I agree with Ranger, you need to go manual operating to 100% and you can see the noise.
By the way this compressor is crazy noise by factory made and especially between 30 and 50% capacity.
You maybe reach -35 or -40 suction pressure but there is only way to be sure what problem you have.

[Superfridge]

Has it always operated like this & something changed recently.
What is Vi set to out of interest, as thought it can be adjusted.
Can you turn economiser off & see what happens

There has been changes this season with production, this is out of our control. No economiser fitted. The VI was set when the compressor was rebuilt 4 years ago by someone else, I have not checked it as I was assured it is correct, it's unlikely to change. No screw compressor should shake like this one was, even at low load. The suction check used to rattle a bit on start up but not like this. I am still leaning towards the pressure in the compressor suction housing being greater than what is in the suction line causing the check valve to slam closed just not sure why? We could lower the suction set points and run it into a vacuum to see but i'm worried the compressor might start walking out the engine room to meet us!

[RANGER1]

Superfridge,
Female drive very noisy at best.
Vi probably does not matter if 40% loaded, as well as it is not over compression.
One possibility is Slide valve discharge end control plated guide slide valve, if worn rotors can rotate & contact rotors.
Another possibility is thrust bearings damaged or worn etc.
Can all be checked on the base with some dis-assembly.
slide can be taken out, look at it & rotors.
Push/pull rotors in out, check end float or bearing clearance.
Don’t know exactly but quests 0.025 to 0.1 mm is normal end float. Male rotor end cover would have to be taken off.
Nothing you want to hear, but if not confident loading it up, no easy fix.
parts a few weeks from supplier
Tough one
You could also check oil filter & magnet for excessive metal first, before all above.

[AKI]

Superfidge I think that you have problem that compressor have BIG vibration with wrong coupling aligment of compressor and el. motor

[Josip]

Hi, Superfridge

Compressor was SAB 163 ...
we had a similar problem with big noise i.e. rattle ... but vithout that strong vibrations
and we found worn slide valve ... made repairing with metallization ...
noise were reduced and compressor run OK ... but that last for short time
(checking oil filter we found metallization material within oil filter)

Then we order new slide valve and problem solved ....

Above was mine expirience and in your case
maybe is not the same problem, but ...


Best regards, Josip

[Superfridge]

Update, the cause of the noise and vibration was due to the failure of the BSV and the failure of the piston seals and shaft seals in the POV. Once we got some service information we started to make progress. The BSV would not hold pressure on the inlet. The POV would not hold pressure within the piston assembly. The sprung seat was ok. The combined leakage was enough to pressurize the compressor suction inlet chamber enough to overcome the pressure and flow opening the suction check valve causing it to slam closed repeatedly. Being an older machine the new POV has to be made and is 5 weeks delivery. We ended up getting new seals made for the POV which is normally a non serviceable item with no parts listed, replacing the BSV and now the compressor is running normally. There is an improved design of suction check that now has dampening characteristics from what I have read. Thanks for all your input.

[RANGER1]

Thanks for update.
From that armchair, did not think of that.

[Josip]

Hi,

Update, the cause of the noise and vibration was due to the failure of the BSV and the failure of the piston seals and shaft seals in the POV. Once we got some service information we started to make progress. The BSV would not hold pressure on the inlet. The POV would not hold pressure within the piston assembly. The sprung seat was ok. The combined leakage was enough to pressurize the compressor suction inlet chamber enough to overcome the pressure and flow opening the suction check valve causing it to slam closed repeatedly. Being an older machine the new POV has to be made and is 5 weeks delivery. We ended up getting new seals made for the POV which is normally a non serviceable item with no parts listed, replacing the BSV and now the compressor is running normally. There is an improved design of suction check that now has dampening characteristics from what I have read. Thanks for all your input.

Thanks for update .... same as RANGER1 ... that was out of
"investigation" ... area .... no experience with damaged
valves like BSV or POV ... I'm glad you solve problem

Thanks for update.
From that armchair, did not think of that.

Me either ... this again prove that "we" must be present on site
to get a complete picture ....

Best regards, Josip

[AKI]

I made overhaul over 50 Sabroe comp.
first time that you have problem with POW valve.
it is very strange.
But ok .
You solwed this problem and its good school for us.
AKI