Oring in Bearing Isolators for Pumps

[ETS2012]

Hi,

Please share some light on the usage of twin O-rings in bearing isolators/ Inpro seal for pump bearing housing.
The standard design is one O-ring in rotating member.Is it possible to have 2 O-rings in rotating member?.
What would be its Pros & Cons. considering that already single O-ring is able to do the job of sealing.

Thanks...

 

[GPRnD]

The only benefit I'd see to having 2 O rings is it increases the frictional driving force.

Inpro also have an O ring between the static and rotating parts (in their Vbxxd model), that is supposed to help seal it vapor tight when stationary (there has been some disagreement on the long term effectiveness of this however). Is it possible you are referring to this O ring ?

 

[Compositepro]

Twin o-rings did not help the Space Shuttle. Twin o-rings are generally not a good idea because o-rings pressure are activated, and the pressure in the gap between rings is undefined, if both rings seal. If you pressurize or vent the space between them then they can improved isolation of one side from the other.

 

[JJPellin]

I believe two o-rings would be useful to keep the rotor running true to the shaft. A single o-ring may be enough to drive the rotor. And, since there should be no significant pressure, the indeterminate pressure between the rings should not be a problem. But, two points defines a line. Adding the second o-ring may help to keep the rotor turning perpendicular to the shaft center-line. At some point, they changed this design from two o-rings to just one. I would prefer two. As shown in the attached sketch, I think some of the designs may still have two o-rings on the shaft.



Johnny Pellin

 

[ETS2012]

Thanks GPRnD, Compositepro & JJPellin.

*GPRnd--- Yes I was referring the VBXXD model.

*JJPellin--- Can you share the any details(model) of such 2 O-rings rotor seals. It shall be more helpful.

 

[JJPellin]

The only ones I am aware of that still use two o-rings are the ones designed for steam turbines. They have one large and one small o-ring on the shaft, as shown in the sketch I attached above. Full details on all of their designs should be available on-line.

Johnny Pellin