Howden balance piston/sleeves

[RANGER1]

Started a new WRVi 255 howden screw recently with VFD drive . Have only been able to run it at min speed 1440 rpm .
-33 SST+ 35 deg C SCT NH3
Oil pressure hard to maintain , but oil pump adequately sized with much larger oil flow than expected going into comp .
Thought about it and could only come up with labyrinth seals ( balance piston / sleeve ) not performing at low speeds allowing a lot of oil past them .
Clearances quite large in howden balance piston / sleeve .
Anybody have any thoughts or experience on above ?

[Mongrel]

Hey Ranger1, if this is still a problem I can ask an associate of mine who has extensive experience on Howdens. What say you? regards Mongrel

[Howdensupport]

If this is the newer WRVi (variable Vi) unit it cannot be very old, does the unit have some history?

The balance piston to sleeve max radial clearance is 0.10mm, any increase does have an exponential affect on yjr oil flow. Similarly worn journal bearings can have the same effect.

[RANGER1]

On WRV255 Howdens my information show balance piston clearance 0.13 mm male and 0.17 mm female from a 1971 drawing .
Would assume clearance is same in Vi model .
Problem is fixed but mainly query labrinth seal at low speed 1440 rpm .
I am under the impression that at lower speeds more oil would flow through them even if clearance standard minimum .
Howdens seem to need more oil flow than anything else on market ( not that there is anything wrong with that ).

[RANGER1]

Mongrel ,
Is that a name that most refer to you as ?

Mine I can't write here .

Can you ask your associate on his thoughts on this matter in due course ,
not urgent .

Thanks , for my own interest only .

[Howdensupport]

Can confirm balance piston radial clearance is 0.10mm, balance piston diameters have not changed in 40 years. I suspect your 0.13 and 0.17 numbers are someones guess at which point the clearance becomes a problem with oil flow.

[petrock]

You say the problem is fixed. How?

[RANGER1]

petrock ,

Nothing to serious that would damage a compressor or anything .
Just unexpected oil flow required to to compressor .

I think balance piston clearances are more than 0.1 mm , maybe Howdensupport mean
0.1 mm per side ?