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Nh3orbust
04-08-2016, 12:25 PM
Hi guys I'm new to this just thought I'd ask the question we currently have a grasso Y
That has bad vibrations at around 42-43hz (Vsd driven obviously) amps, pressures are all spot on oil pressure was high when we found her I know they don't like it that way just wondering we did a thrust check recently and male rotor showed a clearance of
0.11mm and female 0.04mm the manual has been converted from German so it's not making a whole lot of sense but from what I see that's 0.01 too close on the female and 0.01 too far on the male is it possible the male has touched the housing?

RANGER1
04-08-2016, 09:22 PM
Hi guys I'm new to this just thought I'd ask the question we currently have a grasso Y
That has bad vibrations at around 42-43hz (Vsd driven obviously) amps, pressures are all spot on oil pressure was high when we found her I know they don't like it that way just wondering we did a thrust check recently and male rotor showed a clearance of
0.11mm and female 0.04mm the manual has been converted from German so it's not making a whole lot of sense but from what I see that's 0.01 too close on the female and 0.01 too far on the male is it possible the male has touched the housing?

NH3orbust,
In manual I get standard factory discharge end clearance 0.07 to 0.1mm maximum 0.25 mm
If female rotor under minimum could be high spot from debris or something giving false reading.
Male rotor is the only one affected by oil pressure above 350kpa, keep 250-300 max
Did bearings look OK, nice & shiny?
How many hours on machine since overhaul?
Sometimes you can skip a frequency that machine does not like.

Nh3orbust
05-08-2016, 02:09 AM
hi ranger 1 thanks for the response,
I agree with the possibility of debris and had already planned to re test, and also have looked at skip frequencies
and hopfully will have them put in soon but just to confirm the method of testing them we have done the following
1.blown down package
2. disconnected coupling
3. loosened shaft seal cover
4. removed thrust covers male and female
5. set up dial indicator on male rotor and pulled male rotor to discharge end.
6. zeroed dial indicator.
7. pushed rotor away (towards suction end of machine and recorded measurement)

this was done 3 times to confirm measurement on both rotors?

RANGER1
05-08-2016, 09:54 AM
hi ranger 1 thanks for the response,
I agree with the possibility of debris and had already planned to re test, and also have looked at skip frequencies
and hopfully will have them put in soon but just to confirm the method of testing them we have done the following
1.blown down package
2. disconnected coupling
3. loosened shaft seal cover
4. removed thrust covers male and female
5. set up dial indicator on male rotor and pulled male rotor to discharge end.
6. zeroed dial indicator.
7. pushed rotor away (towards suction end of machine and recorded measurement)

this was done 3 times to confirm measurement on both rotors?


Sounds good to me.
Best to use metric dial gauge for accuracy.
If compressor has 20 to 25 thousand hours time is probably up for overhaul.
Grasso don't really worry about minimum readings as they are concerned with maximum, showing worn thrust bearings.
Discharge pressure forces rotors to suction end when running, high oil pressure influences balance piston forcing it into discharge end on male drive rotor only.
Of course some situations like starting package with low pressure in it or unloaded operations can effect that as well.
Does not sound like rotors in end housing yet

Nh3orbust
05-08-2016, 11:35 AM
Thanks for the help mate have to keep looking for the issue I guess

RANGER1
05-08-2016, 11:37 AM
Thanks for the help mate have to keep looking for the issue I guess


Check your email for info

RANGER1
09-08-2016, 10:31 PM
Nh3,
I sent some more info, check email

Josip
10-08-2016, 11:59 AM
Hi, Nh3orbust :)

welcome to RE forums .... the best is to start here
http://www.refrigeration-engineer.com/forums/forumdisplay.php?72-New-to-RE

to introduce yourself to us ... but you can do that any time;)


Hi guys I'm new to this just thought I'd ask the question we currently have a grasso Y
That has bad vibrations at around 42-43hz (Vsd driven obviously) amps, pressures are all spot on oil pressure was high when we found her I know they don't like it that way just wondering we did a thrust check recently and male rotor showed a clearance of
0.11mm and female 0.04mm the manual has been converted from German so it's not making a whole lot of sense but from what I see that's 0.01 too close on the female and 0.01 too far on the male is it possible the male has touched the housing?

If I understood you well ... your measures (0,11mm and 0.04mm) are play of axial bearings only (this is not measure of axial clearance) .. i.e. it is time to replace them immediately ...

new axial bearings should not have bigger play then 0,03-0,04 mm or even less depending on bearing size, construction of axial bearings housing and tightening torque which determine play of new axial bearings and that should be noted.



.. to set axial clearance (there must be another set of shims for this purpose) you need to release bolts which are keeping axial bearings assembly then you need to pull rotor/s by hand (one by one) to discharge end (hard touch between rotor and housing) this is your zero position for rotor in question (put dial to zero) ... then tight bolts again by the torque from manual ... this reading will show you how far you are from discharge end i.e. axial clearance ... now, further push of given rotor towards suction will give you play within axial bearings - and this is what you measured ... if you did not touch any other bolt or nut i.e. release any of them ...


Hope this is of some help to you .. if you need more help do not hesitate to ask ... of course it is possible that I misunderstood something ...


Best regards, Josip :)

RANGER1
10-08-2016, 09:32 PM
Josip,
I understand exactly what you describe, as this method determines minimum discharge end clearance, then checks for axial play.
Nothing wrong with that, however Grasso manual & course does not ask to do that, but as how Nh3 describes it.
If you get a new machine a certificate is supplied with factory build sheet giving clearances, which you can then compare when checks are carried out 5-8000 hrs is recommended & how described by Nh3.

Other manufacturers like Mycom are only interested in minimum end clearance & do not ask for axial play.
Howden similar, but suggest check axial play & if more than 0.01mm then replace.

Josip
11-08-2016, 10:11 AM
Hi Ranger1 :),

Grasso procedure and checks are a little bit different from other manufacturers ... there must be some reason behind ... which we do not know now ...

I believe it is time to replace axial bearings (my warm suggestion to Nh3orbust) ... that is quite cheap procedure ... we do not know anything about running hours for that compressor ... high oil pressure is not welcome causing a lot of friction and wear ... and should be adjusted too ...

in practice ... sometimes we need to replace axial bearings far before recommended working hours and sometimes far after recommended working hours because they are still within allowed tolerances ...


Best regards, Josip :)

podik
16-08-2016, 08:16 AM
Hey, try to open / close the valve on the cooling discharge. Sometimes the oil flow creates unpleasant sounds and resonances in the oil pipeline.

Sorry for my English :-)

Nh3orbust
24-08-2016, 05:21 AM
Hey guys sorry been away on honeymoonI really appreciate the replies as with what ranger 1 said the thrust set up is different with the grasso
Mycom, Howden, stal and some others have the nearly exact same set up
from what I can gather correct me if I'm wrong also
the thrust is set by the machining of the Bearings when installing the bearing covers they press the outer of the bearing inwards creating face gap and providing a spring like pressure to them again correct me if I'm wrong ranger1 mentioned this and I may have taken it the wrong way high oil pressure will drive the male rotor against the bearing covers (the big coned out washers found inside the covers bend) and the rotor will touch the discharge end?
We will be looking at swapping out the bearings a precaution Josip as you mentioned this machine is only 15,xxxhrs old
The reason I am worried about this is their is a package of the exact same design installed at the same time next to it without any noise (less hrs though around 13,xxx) I have already checked oil injection thanks podik. The installation is quiet poor wehave noticed the concrete base it was placed on isn't supportive (one whole side was nearly off the ground) we had this all shimmed to correct it, the discharge line ran nearly 3 meters (mouth of machine then UBend under the machine under the motor and into the vertical oil sep) we also noticed the vertical mount Viking oil pump frame was cut and re installed during installation or possibly before And oil sep has been put on the piss using pieces of steel under the flange mounts to help correct it maybe because it wouldnt line up with oil cooler we can tell this because of the different tone of the paint and the massive gap and filler weld used and obviously putting a level on the sep

RANGER1
24-08-2016, 09:20 AM
NH3orbust,
Check your email as describes how to adjust clearance with inner & outer spacer.
Keep in mind if you install new bearings clearance could still be the same if high spot on end of rotor.
If you adjust to give perceived correct end clearance it may be to much in reality.
If only 15000 hrs on bearings it would be very premature to change, especially once you find out price of them if you go genuine.
Vibration analysis could help determine, but that cost money a s well.
A laser alignment would also be recommended, maybe vibration guy could do both if you have no access to one especially from what you describe.
Some machines are noisier than others, just the way it is, hard to determine what's what.
Have a good feel around package for vibration & if every thing tight