Seal Squeal

[RS82]

We were testing a dual - tandem metal bellows seals (rotating seal heads) on a vertical pump..the outboard seal has a pumping ring for the plan 53B barrier fluid..we had injected the barrier into the seal at the location of 2 O'Clock and piped up the barrier out at 12 O'clock..the seal squealed a lot..and then we switched the piping around and the seal stopped sqealing..we did this twice and the same thing happened..whats the logic behind this?

 

[JJPellin]

The seal drawing should specify which port is supposed to be “in” and which port is to be “out.” If this seal has a pumping ring, it is especially important to get this right. One of these ports could be drilled radially and the other drilled tangentially. I suggest the following:

1. Review the drawings and verify which port is which. The seal gland should also be stamped to indicate BI for Barrier In and BO for Barrier Out.
2. Verify if the ports are radially drilled or tangentially drilled.
3. Review the seal design for pumping ring configuration. If the pumping ring is rotationally specific, is it designed to match the rotation of your pump?
4. Make your connections correct for the drilling (radial or tangential), shaft rotation and pumping ring design.

If it still squeals when piped correctly, then the seal manufacturer may have made a mistake and installed the wrong pumping ring.


Johnny Pellin

 

[flexibox]

i have experienced somthing similar before but never arrived to a conclusion. Not an easy one to pinpoint! however the noise can only come from the faces or rubbing of the pumping ring. have you inspected the OD of the pumping ring? also with bellows seals you can get Slip Stick! see extract from internet

SLIP STICK

A lack of lubrication between the seal faces can cause a destructive form of vibration called "slipstick". Without proper lubrication the lapped seal faces try to stick together, but "slip" when the seal drive mechanism engages the drive lugs and inertia accelerates the faces off of these lugs. The faces then slow down as a result of the poor lubrication.

This alternating "slipping" and "sticking" causes severe vibration, with a resultant "chipping" at the out side diameter of the carbon face, along with drive lug and slot wear.

Mechanical seals that use an o-ring as the secondary seal utilize the o-ring as a vibration damper. Metal bellows seals have a severe problem unless a damper is designed into the product.

It is hard to relate this to your problem but you may not be getting the same flows depending on pumping ring direction. Good Luck!

PS: Do you have sufficient delta P on outboard seal? perhaps insufficient lubrication on outboard seal.

 

[1gibson]

Are you sure it is set correctly? Barrier fluid get on the shaft underneath the set screws and cause it to slip? I've seen a collar "walk" up due to slipping on the shaft, until it was stopped by the faces being smashed together. Squealed like a pig.

Axial position is ok? Shaft can move due to momentary upthrust at startup, and/or downthrust at rated flows.


In at 2, out at 12, so the rotation of the pump is clockwise from above? Is the rotation correct on the seal dwg?