Gas seal failure

[Reifleman2]

Just looking for brainstorming:

What could cause a dual pressurized set of gas seals on a split case pump (7 impellers) to fail the seals, touch off on only one part of the gland plate (shaft rub of about 90 - 180 degrees) and shear off some dog-point set screws. (3 failures in less than a month, 1 drive end 2 thrust end)

Lots of things have already been ruled out: Push bearings are unaffected (not even damaged), shaft is true, alignment is dead on, vibrations are low. The shaft is a softer material, 4".

This is becoming a "look for the unicorn" problem, so any ideas or suppositions are welcome.

Thanks.

 

[MikeHalloran]

Figure out why the 'push bearings' (thrust bearings?) are apparently not carrying any load.


Mike Halloran
Pembroke Pines, FL, USA

 

[Reifleman2]

Excellent idea. I inquired about the thrust bearings and the drive end bearings, supposedly everything is within clearance and tolerance. They performed a float test, took measurments and show it all to be within tolerance.

This part doesnt make any sense. It seems impossible that a 3.25" shaft could touch off, run a wear pattern and blue up the gland plate when a set of bearings 10" away are unaffected and show no damage.

 

[hydtools]

Is there a matching wear pattern on the shaft?
The gland plate moved out of alignment?

Ted

 

[Reifleman2]

There is a matching wear pattern on the sleave. Everything seems to be in alignment, and the gland plate is an incredibly snug fit into the stuffing box.

Most probable cause of wear: Gland plate movement (of .022 or more to surpass clearances) to touch off on the shaft/sleave.

Why we dont think thats it: Tight gland fit, good alignment, no bearing wear, no bolt degredation etc. None of the other things that would be wrong if it had shifted.

It LOOKS like a gland plate shift, but no other effects of somthing like that happening.