BF Water Pumps, leaky seal

[v7042800]

I have a customer with a few BF water pumps (1000 psi, 540 F). These pumps are 1-stage, dbl-suction impeller, horiz-split case. THey they keep trashing the seal on the coupling side after a few months run. Seal comes out with dynamic gasket blown and heavy rubbing marks on the ID of the gland plate on one side only. The seal pumping ring has a corresponding rub on one side only.

The other seal on the other end is in good condition. Can someone give me an indication of what may be going on?
I dont have any info on how the customer warms up the pump or when they align the coupling.
thank you.

 

[flexibox]

Need to ask a few questions first.

How old is the pump?
How long has the this been happening?
How many times have you seen this occurrence?
Do you have high vibration in operation?
I would start by inspecting the pump. Check that the pump shaft is in centre line perhaps someone did some machining. Doing this needs time!
Check shaft is straight and not bent. Is the pump cavitating causing the shaft to deflect and picking up on the pumping ring OD.
Perhaps a solution may be to open up the clearances to the pumping ring! Do you know what the clearances are? If this is too tight then the pump may be operating ok but the clearance may need to open up a little to eliminate contact. This will affect pumping ring efficiency but may solve the contact problem.


Trust this helps

 

[JJPellin]

I don't understand how these pumps develop 1000 psi in a single stage. I assume these are circulating pumps, not feed pumps. I would look for diferential thermal expansion betrween case and shaft. A 410 SS shaft can result in axial intereferences in a carbon steel case at high temperatures.

If that is not the problem, then poor concentricity could be an issue. This is described as multiple pumps with the same failure mode. One event of poor machining would not result in this problem.

Johnny Pellin

 

[v7042800]

The SUCTION presure on this pump is 1000 pai and the seals are at this presure. Have had this ocurrence two times; one on each pump. Not sure about the vibes but will ask. No cavitation reported. Pumps are in a remote site in a different country and I have not visited the site.
I have physically inspected one seal that the user sent me, the seal on the coupling side. Faces exhibit some flashing, dynamic gasket has large chunk torn off and is blistered, hard-coated surface on the sleeve does not exhibit much fretting.
End user reports normal temperatures for the plan-23 product and coolant IN/OUT legs. Metal hardware disclored in a dark hue...not quite as dark as gun metal)

The fact that the same side of both pumps (coupling side)are having seal issues makes me wonder. Free end of the pump appears to be working well...
I have seen pictures of one other failure with the dynamic gasket damaged in the same way; big chunk torn off, blistered and exhibiting minute tears along the surface.
What would cause a bent shaft or excessive runout on the coupling end only..?
thank you for your responses..!!!!!

 

[JJPellin]

That is why I mentioned differential thermal expansion. If the shaft was 410 SS and the case was carbon steel, the shaft would grow relative to the case. It would be fixed at the thrust bearing (which I assume is on the non-drive end). One seal (closest to the thrust bearing) would see very little shaft growth. The opposite end seal would be severely over-compressed as the shaft grew through the seal chamber. If the free float of the radial bearing was not sufficient for the thermal growth, the shaft would go into compression and could buckle.

Even if the shaft and case were both carbon steel, this could occur during a start-up transient if the pump was started up without being warmed up. If you hit a cold pump with 600°F product, the shaft will grow much faster than the casing and this can over-compress one seal or drive the shaft into compression before the case growth catches up. I would make sure that the shaft and case materials are correct and verify that they have a proper warm up procedure before start-up.

Johnny Pellin

 

[v7042800]

Thanks again