oil seals

[TonyCro]

Hi chaps,

I'm in a struggle - we have a large vertical pump/storage unit and the bottom guide bearing is loosing oil out of the upper seal, by how much no-one knows but the feeling is quite a lot - technical reporting at its best!

We're going to re-set the seals clearance back to design ~0.15 to 0.3 on 1126mm dia and ~600 to 750rpm. the upper seal chamber is pressurised and I'm going to look if I can boost the pressure to increase the sealing effect.

But I'm tempted to fit an additional PTFE seal at the bottom at a tighter clearance of 0.08mmm (guide pad clearance is 0.0875mm max) to limit the amount of oil that can creep up the rotor.

All these are simple steps but the owners engineer has asked for calculations to prove the effectiveness of the new seal and here I'm at a loss - are there any calculations, ideally fairly straightforward, to demonstrate that this is an improvement ?

many thanks
tony

 

[Tmoose]

Is this a standard design?
I'm having trouble visualizing it.

Air purge type sealing to supplement non-contact/labyrinth seals can be tricky. Horizontal shaft applications (precision spindles) require some degree of careful internal air flow management to avoid being pumps or just having big unprotected voids.

http://www.setcousa.com/files/Literature/S_0006_1_AirShield_Broch.pdf