Gear Pump Seal Failures 1

[JRLAKE]

Hello everyone,

I have been stumped by a series of mechanical seal failures on a gear pump.

Fluid:
Printing Ink
200 Degrees F Max
200 cps max
No solids present

Pump:
Gorman Rupp Internal Gear
Model GHA3NM3-B
Driven at 205 RPM with 5 HP Gearmotor
30 GPM @ 100 PSI

Mechanical Seal:
Single Internal Unbalanced Pusher
316SS spring and carrier
Stationary Face: Silicone Carbide / Viton oring
Rotating Face: Silicone Carbide / Viton boot
Seal assy cut sheet:

System:
Truck Loading
500 Gal Tank feeds suction with 2' run of 3" pipe directly to suction. No elbows. Discharge through filter assy to truck.

Problem:
Viton boot is shearing between rotational face and carrier. It appears that the seal faces are sticking together. The boot and carrier are rotating as they should, but the face doesn't want to rotate and the resulting torque is shearing the viton boot. This failure has occured five times on five different pumps. There is no sign of abrasion anywhere. There is no sign of chemical attack. There is no sign of excessive heat.

Manufacturer has no answer. My mechanical seal vendor has no answer. I think a positive drive is needed between carrier and seal face, maybe by means of a pin. Right now, the arrangement is a friction drive, in which torque is transmitted to the rotating face via a compression fit between carrier and viton boot.

Any ideas? Pictures below:

Failed Boot

New Seal Showing Carrier / Face Arrangement

 

[MikeHalloran]

It seems odd that both faces of the seal would be made of the exact same material. Not that I know much about mechanical seals.

If the product could withstand a tiny bit of contamination, a fingerprint of silicone grease on the seal faces might keep them from sticking until they've become accustomed to each other. Again, not that I know much about mechanical seals...





Mike Halloran
Pembroke Pines, FL, USA

 

[hydtools]

Just observing from the parts arrangement I see a spring guide. If it is not there, the spring would contact the stationary housing and not rotate with the bellows it is supposed to preload and rotate with. Maybe the spring or spring guide is the problem.

Ted

 

[JRLAKE]

Thanks for the responses. I won't say it is extremely common but I frequently use like faces on mechanical seals, depending on the application.

Ted, I don't think this is happening but I will check, interesting point. The clearances are very tight within the seal chamber so it is a possibility, but I saw zero signs of wear on the shaft. If it was contacting the seal chamber wall it would also be contacting the shaft.

Perhaps I should have posted this in the mechanical seal engineering forum.

 

[bk19702]

Is the 200 cps viscosity at operating temperature? What is the viscosity at ambient conditions? Also, is there a drive device between the cage and bellows? If so, do the tabs on that band appear worn? Since this is apparently an intermittent process, the torque at startup is most likely the culprit as you have guessed. The idle periods are allowing the process fluid to set up at the face and therefore increasing the breakaway torque required. The face finish applied to the hard faces will have a lot to do with this as well; more often than not hard face materials will have an affinity to 'bond' to one another during idle periods. One suggestion would be to try a matte finish on both face surfaces (increasing the roughness of the face and therefore reducing the potential for high startup torque). Is there any way to warm / insulate the seal area between operations? If you can keep the seal cavity warm, you may keep the fluid viscosity down to the point where it doesn't set up between the faces, which again, sounds like what is occurring.

 

[FACS]

Is there a reason you can't try a standard Viton Lip seal instead of the mechanical seal?

The only reason we put mechanical seals in our paint pigment pumps was because of the abrasive solids. If the ink has no solids, see if there anything preventing you from experimenting with a lip seal or two.

Charlie

http://www.facsco.com

 

[JRLAKE]

Thanks Charlie, I am actually considering that option with a Teflon triple lip seal. A triple lip seal is the only option the vendor has available as far as lip seals are concerned.

 

[chief]

Unusual to have similar materials on the rotating and fixed seal. Normally have a ceramic or stainless fixed seal face with the silicon carbide rotating.
A spray of light oil or WD40 on the faces before @first run' will help to 'bed' the faces in.

Offshore Engineering&Design