Stal S51 Rotor damage

[Scott B]

We have just pulled down a Stal S51 (R22) compressor for inspection. The machine looks to have had a pretty tough life, very dirty for a ***** machine.
The thing that has us a bit puzzled is the male rotor. The wear strip is present on about 1/4 the length of the rotor then disappears completely, the rest of the rotor has no strip whats so ever. The 3/4 of the rotor with out the strips looks like it has been machined that way, no sharp feathered edges but if you did not no better you would say the slide valve has hit it.
When you put the slide valve next to it it does sort of line up but the other rotor has no signs of damage and the casing is fine. Does anyone have any theories on the missing wear strip?

[Sandro Baptista]

Maybe something had happen when it run at beginning and then the wear did a kind of sharp disappear...

[CHIEF DELPAC]

Scott B Years ago when I was a rookie in refrigeration I saw a Dunham and Bush NH3 comp. that had severe rotor damage simular to the Stal comp. The damage was so bad that the comp. was not pumping it was just free wheeling. The cause was atributed to bearing wear that changed the clearances and allowed the rotors to grind away on each other and the end plate of the comp. The comp. was sent back to the factory for a rebuild. The rotors had to be recast as they were not repairable. C.D.

[Sandro Baptista]

We have just pulled down a Stal S51 (R22) compressor for inspection. The machine looks to have had a pretty tough life, very dirty for a ***** machine.
The thing that has us a bit puzzled is the male rotor. The wear strip is present on about 1/4 the length of the rotor then disappears completely, the rest of the rotor has no strip whats so ever. The 3/4 of the rotor with out the strips looks like it has been machined that way, no sharp feathered edges but if you did not no better you would say the slide valve has hit it.
When you put the slide valve next to it it does sort of line up but the other rotor has no signs of damage and the casing is fine. Does anyone have any theories on the missing wear strip?

Was it a routine inspection or do you have detected something wrong?

[RANGER1]

Have a look at guide block & rail , is it worn.
Also can you see contact or shiny surfaces on top of slide valve .

Rotor bearing clearance should also be about 0.004" whats there journal / bearing condition & clearance ?

Slide valve & housing clearance should be about 0.002-0.004" clearance as slide can also lift this clearance is excessive causing contact .

Would say you have combination of all the above .

Unworn part would be at inlet end of compressor where there is no slide valve travel .
I know of at least 2 complete S51 packages for sale going cheap if your interested .

[RANGER1]

What Vi have you got ?

[Scott B]

Hi Ranger1
This machine was sent to us and we don't have any history on it but we now think it has been rebuilt at some stage and the damaged rotor was cleaned up. The journals and mains are in good nick the slide valve has some feathering on top but not the worst I've seen, but is a bit sloppy in the housing. Would be interested in the used machines you mentioned this one is 2.6 VI, I maybe able to help you out with some Sullair info.
Can I contact you via email or phone?
Cheers Scott

[CanadianIce]

Recently had a Howden XRV204 with the same problem. The slide valve and guide block were worn allowing the slide valve to rotate slightly in its bore. Once the slide valve and rotor rubbed for awhile, the wear was great enough to allow the oil pressure to lift the slide valve into the rotor and continue grinding away. Compressor was replaced.

C Ice

[Magoo]

Scottie.
the screw is screwed, looking at pics the rotors are suffering from hot oil, the lip seals are gone, which means the mains are worn beyond tollerance, the thrusts are out to lunch as well.

[Scott B]

Hey Magoo,
Thats the weird thing the mains and journals are fine, thrusts in good condition. It appears that the machine has been overhauled even though the rotor and slide valve were cactus. Yes the oil is very dirty and been running very hot.
Thanks for your feedback.
Regards Scott

[dwrefrigeration]

is the compressor economised,those are not wear strips they are designed to slot into the female rotor to give a good seal,If the compressor is economised something may of entered through to eco port and damaged the rotors from the eco port onwards

[RANGER1]

Scott chech your private messages .