screw compressor end play checks

[danod]

Just wondering, when end play or shaft run out check's are done does anybody de-pressure the compressor before performing checks or do you put your dials on and check with pressure on.

[Grizzly]

Hi Danod.
The fact that you ask the question, worries me somewhat!
How do you expect to measure the end float with pressurised forces within?
Grizzly

[danod]

Grizzly, I don't think de-pressuring is necessary. If your compressor is off and pressures have equalized I don't think you would have any apposing forces. In the past I have made checks with units pressured up and then de-pressured and the results have been the same. I asked mostly out of curiosity and to seek out other opinions. I appreciate your response.

[Grizzly]

Fair enough Danod.
We all have differing practices, only I have yet to come across a manufacturer that states "Whilst Pressurised".
That does not mean that your method is flawed, as you state.
Just not in any manual!
Surely when pulling forward and back, if the clearance is bigger than 1 1/2 thou you would break the seal on the Shaft Seal?
Resulting in a potential refrigerant loss! Which is not allowed under our F Gas Regs.
That having said, unless you remove the s/seal assembly its spring could influence the test result.
So unless the comp is stripped down sufficiently your end play result is likely to be flawed.

However in fairness to you your method could form a good first line defence. Meaning random checks and when sufficient wear is detected a more thorough inspection could be planned.
I tend to refer to the screws operation and run hours nowadays, even the drip rate of oil from the S/Seal would be a useful indication of wear.

Cheers Grizzly

Grizzly

[PaulZ]

Hi danod
When you say you have done an end play I take it you are referring to a thrust bearing check. If the compressor is pressurised you could only check the driven rotor. Shaft alignments can be done with the compressor pressurised with no problem.
As Grizzly has said it is a good first line check but I would not rely on it, an I agree with the other points he makes.
Paul

[danod]

Hi Grizzly. I would think that most seals with springs have more than 1.5 thou float. Even with carbon wear. We do these checks on a regular basis, a preventive measure. If I get 1.5 thou. end play I am usually telling a customer he should be considering further inspection. I rely on compressor hours and seal condition as well. PaulZ, end play or rotor float is what I call it. I place a dial on the end of the shaft and move the shaft in and out. If the dial goes from 0 to 1.5 thou. and stays that is end play or rotor float. If the dial goes from 0 to 1.5 thou. and back to 0 that is deflection. If I could post a video I could show you a mycom with 16thou. end play or rotor float that had 53000 hours on it. It was pulled and overhauled. Should be doing some more checks soon will have to check both ways. Thanks for the feedback.

[Grizzly]

Hi Danod.
You guys must have customers with deep pockets!
Most of ours would baulk at the labour rates involved in stripping drive couplings etc. to check specifically the end floats.
Although if you are talking about run hours such as those you mention. What customer could argue. if you are
successfully keeping plant running with extended hours. Then Fair play to you!
Grizzly
I know on Mycom V they recommend IR at 24000hrs.

[PaulZ]

Hi danod
Did the Mycom with 16 thou have stuffed thrusts I would have thought so. Also I suspect there would have been damage to the ends of the rotors and the end case if the rotors can move around that much given the rotor end clearance on a Mycom would be between 4 thou and 8 thou (from memory) depending on the size.
If I put a dial on the end of the rotor and moved it back and forward I would recommend an overhaul or thrust replacement if it was more the 1 thou. Thrust movement (end play) on new bearings is about 1/4 thou.
Regards
Paul

[RANGER1]

Hi Grizzly. I would think that most seals with springs have more than 1.5 thou float. Even with carbon wear. We do these checks on a regular basis, a preventive measure. If I get 1.5 thou. end play I am usually telling a customer he should be considering further inspection. I rely on compressor hours and seal condition as well. PaulZ, end play or rotor float is what I call it. I place a dial on the end of the shaft and move the shaft in and out. If the dial goes from 0 to 1.5 thou. and stays that is end play or rotor float. If the dial goes from 0 to 1.5 thou. and back to 0 that is deflection. If I could post a video I could show you a mycom with 16thou. end play or rotor float that had 53000 hours on it. It was pulled and overhauled. Should be doing some more checks soon will have to check both ways. Thanks for the feedback.

Danod,
After compressor is removed for service, do you overhaul in house or sent to others?
Only asking as do you receive a report on them as to what condition is, report on clearances wear, damage etc.

Sometimes it would be nice to know to possibly make judgement on cause of failure or wear.
OK you ran this machine for over 50000 hrs. What duty was it running, oil quality, oil & discharge temps, liquid injection & set point, oil injection reg valve open to much, oil filter ever damaged, oil samples, condition monitoring etc.
All well to check male or driven rotor float, but what about all the other possibilities of maintaining compressor & package!
Maybe you do them already?

[danod]

Hi Ranger, we overhaul Mycom's, Vilter's ,Howden's, Frick, and Sullair screws and recip's in house for screws and field and in house on recips. Inspect and measure all parts. usually send rotors for balancing and machining if required. This particular compressor was a first call too this gas booster to assist the mechanics in replacing the seal. In hind site I should have done the end play before removing the old seal but was given wrong info on the history of the compressor. It was shut down because of oil pouring from the seal. I don't know what conditions it runs at except it is for natural gas out of the ground and into a pipeline to a gas processing plant. This overhaul was sent to another shop and they did the start up after. We will be doing yearly checks to it or so I was told.

[danod]

Grizzly we have customers that will run compressors till they crater and become boat anchors and others that spare no expense to maintain the equipment. They are all large industrial plants one in particular has a mycom 320 and a 250 screw on one chiller that both compressors run 100% loaded all the time. (Only for 6 to 7 months of the year. the rest of the time mother nature provides the cooling.) On the other hand we have a customer that every year we replace the thrust bearing and the seal on a 12cyl mycom r-22 system. It only runs for maybe 1500/2000 hrs a year. They are not interested in letting us do the investigation as to why it keeps failing.

[danod]

PaulZ, this compressor was a mycom 400. It would have tilting pad thrust bearings if that is the same as stuffed thrusts. The overhaul went to another company so I did not see what damage was there. I will ask as I know the the guys who did it. I have had mycoms with 1.1/4 to 1.1/2 thous. end play where they have been run for another year before being overhauled. That can be risky but the customer makes the final call.

[Grizzly]

Good interesting answers Danod.
Thanks Grizzly

[sgull]

Hi Danod
When you are measuring the float on rotor without removing the shaft seal cover you are really only measuring the bearing clearance and not the clearance between the rotor and the discharge end housing. This is only useful if you know what the original bearing clearance was for comparison. With the Gram and Frick screw for example you have a very strong thrust plate pushing the rotor and bearing assembly away from the discharge end cover. To properly measure the end play you need to remove the pressure of this plate. Of course you are only checking the drive rotor with this method.

[RANGER1]

Hi Danod
When you are measuring the float on rotor without removing the shaft seal cover you are really only measuring the bearing clearance and not the clearance between the rotor and the discharge end housing. This is only useful if you know what the original bearing clearance was for comparison. With the Gram and Frick screw for example you have a very strong thrust plate pushing the rotor and bearing assembly away from the discharge end cover. To properly measure the end play you need to remove the pressure of this plate. Of course you are only checking the drive rotor with this method.

sgull,

Would it be correct to say a Frick/Gram has approx 0.002" - 0.005" thrust bearing end float.
In that case you would have to ideally know what it was from new.

[sgull]

sgull,

Would it be correct to say a Frick/Gram has approx 0.002" - 0.005" thrust bearing end float.
In that case you would have to ideally know what it was from new.

Hi Ranger
Maybe I am mixing up bearing float and shaft end clearance.
The Gram/Frick end clearance is slightly higher than the the likes of Howden since they only have a single thrust bearing on each rotor. depending on the compressor size the smaller unit (gram GSV50/ Frick TDSH163) would have an end clearance between the rotor and the discharge cover of approx, 0.15 to 0.18mm. as the compressor size goes up the allowable clearance goes up. For example the Gram GSV 147 (TDSH233s) would have a clearance of 0.18 to 0.21mm. The measurements taken by not removing the shaft seal cover will not measure this but will measure the bearing clearance.While this is useful you are only measuring one rotor and would need to know the clearance of a new bearing to determine if any wear has taken place.

[RANGER1]

Hi Ranger
Maybe I am mixing up bearing float and shaft end clearance.
The Gram/Frick end clearance is slightly higher than the the likes of Howden since they only have a single thrust bearing on each rotor. depending on the compressor size the smaller unit (gram GSV50/ Frick TDSH163) would have an end clearance between the rotor and the discharge cover of approx, 0.15 to 0.18mm. as the compressor size goes up the allowable clearance goes up. For example the Gram GSV 147 (TDSH233s) would have a clearance of 0.18 to 0.21mm. The measurements taken by not removing the shaft seal cover will not measure this but will measure the bearing clearance.While this is useful you are only measuring one rotor and would need to know the clearance of a new bearing to determine if any wear has taken place.

Sgull Grasso is interesting as it checks discharge end clearance & bearing wear, as
they give what was factory assembly clearance.
If clearance is higher than factory measurement, then this is the amount of wear.
If there is a high spot on discharge end faces, then it all means nothing!.
When assembling a Frick it states in manual bearing play & all are a bit different, which can also effect
discharge end clearance to a minor degree.
Frick you use their special jacking tool which draws rotor towards suction end, giving maximum DEC,
then bearing play can be checked to give minimum DEC
Kobelco is same story.

PS not trying to tell you anything, just discussing the general points, as nothing much happening in Industrial these days.

We run Mycom boosters to 50000 hrs before recommend service with no problems at all, high side 30-40000.
Check nothing except filters & coupling alignment.
Just did a 320 L high side with more than 60000 hrs.
Interesting damage to both main & side bearings, female rotor only.
It was overdue but no damage to speak of.
We also have a 6WB on R22 with constant damage to thrust face running against crank end face.
You can get a special thrust roller for this face, but Mycom suggest different crank for this application (suction 400 kpa to much load on bearing). Basically we are stuck with it as well!

[sgull]

Hi Ranger
We would normally carry out a service based on running hours or if something indicated that we should take more immediate action. This would be things such as increased discharge temperature, result of an oil analysis or change in noise levels. If the compressor is a female drive or if the customer is mad enough to use liquid injection oil cooling than we would reduce the frequency of the service intervals. Compressors such as Mycom, Howden , Stal or some older Dunham Bush units are work horses with double thrust bearings and would probably be ok for 60,000 hours (not promoting any particular units, there are probably many more). The likes of Frick or Gram have single thrust bearings. If you leave these for 60,000 hours you have nothing left. Compressors such as the Vilter mono-screw have a 15 year bearing warranty but that is another issue.

[Tycho]

Excuse my ignorance, but how to you even check the end play without removing the bearing covers, thus opening the compressor/system to gods free nature and refrigerant unless you depressurize and remove refrigerant first by AT LEAST closing the suction valve

[RANGER1]

Excuse my ignorance, but how to you even check the end play without removing the bearing covers, thus opening the compressor/system to gods free nature and refrigerant unless you depressurize and remove refrigerant first by AT LEAST closing the suction valve

Tyco,
The way i understand it you would isolate electrically, remove coupling guard & coupling centre.
Using a lever, say a piece of timber or some sort of lever, push pull drive rotor in & out recording with dial indicator any movement.
To me it's a half job so would not normally do it.
If you were say changing a shaft seal of something, then may be incorporate it check while doing it & coupling alignment.
To just move rotor in & out on some compressors like Frick, may even disturb shaft seal & make it leak.
Grasso suggest check thrust clearance every 5000 hrs, that's confidence for you!

[sterl]

I don't see much purpose to knowing the extent of movement Ranger describes, I believe the only thing you are checking is bearing play on one rotor, and in one direction unless you can set up to put a serious pull on the driven shaft.

I've seen (just once...) this done with a pneumatic sleeve on each side and a big plate on the shaft end so the shaft can be both pushed and pulled....Machine at no pressure but still stinking. It stunk a wee bit when the shifting was being done; when it was put back together and the discharge valve opened the seal did leak....Got to believe one caused the other, though I was not there long enough to see the seal internals come out.

[Tycho]

Thank you Ranger1 for your reply, and thank you for saying you consider it half a job

English is my second language, so excuse me if I am misunderstanding...

"end play" translated to Norwegian is "end clearance" meaning the clearance between the discharge side of the rotors and the body of the compressor, and I am disturbed in so many ways that someone thinks they can do this without opening the compressor... because usually the thrust bearings are, for some reason, on the opposite side of the compressor from the drive end... and most screw compressors have "end covers" that have been precisely machined or have been shimmed to give the compressor it's "end clearance" and while it's fully possible on a screw compressor to do this on the male drive end, since the o-ring on the thrust bearing cover is so far in that you can release the tension on the thrust bearings and check the end clearance on that side...

Excuse me, I'm just writing out of pure disbelief here, just ignore it... it's just so far beyond my belief what kind of professional service technician would do a half botched job on a compressor... is it to get a total overhaul job 3 months after he said that the compressor was "good to go for another 6 years" or was it to see them a new compressor 6 months after he said "naaah, the manufacturer says three years, but it can run for 10 mate" and then when it suffers a catastrophic breakdown in 5, the same guy comes back and says "Yeah mate, I told ya, three years is the max on these machines, five at the max if you push them" it just boggles my mind that some of these people are still in business, I'm sorry if I'm ranting... I really am, but how do these people keep in business

[PaulZ]

Hi Tycho
I have to agree with what you have said.
I refer danod back to my second post regarding the .016" rotor end float. the term "stuffed" means the bearings are totally worn out.
If you are only checking the drive rotor without dismantling how do you know whats happening inside teh compressor.
I still maintain that if you are getting 16 thou movement laterally on the rotor you have a major problem and that compressor should be dismantled and inspected. With that amount of end float / movement I would suggest the rotor has been making contact with the casing and this can only be determined by dismantling the compressor.
As has been stated this is only half a job and I am amazed that this could be done by a qualified trades person.
Regards
Paul

[RANGER1]

I think thing may be taken out of context.
The initial statement indicated it was a simple check on drive shaft & whether pressure or no pressure.
If you carried out an annual coupling & alignment check which I don"t think is over servicing, then if possible lever male or driven rotor in & out if practical,

Each country & Region do different things based on their experience & knowledge.
The large end clearance found on the Mycom was a good outcome from this check in that case.
Other people on this forum rave about condition monitoring, oil analysis, vibration etc.
There are good & bad clients, some have money, some don't, some are lucky, some are not.

[Tycho]

I think thing may be taken out of context.
The initial statement indicated it was a simple check on drive shaft & whether pressure or no pressure.
If you carried out an annual coupling & alignment check which I don"t think is over servicing, then if possible lever male or driven rotor in & out if practical,

Each country & Region do different things based on their experience & knowledge.
The large end clearance found on the Mycom was a good outcome from this check in that case.
Other people on this forum rave about condition monitoring, oil analysis, vibration etc.
There are good & bad clients, some have money, some don't, some are lucky, some are not.

As I agree with that Ranger, there are "service technicians" and Service Technicians.
The ones that do a bodge job on the 10.000 hour service may save the client the 15.000 hour service, but they dont save the client replacing the whole compressor at 17.000 hours...
It's gonna happen, don't deny it