high pressure piston seals

[raheeli]

What are the leak paths involved in this kind of high pressure piston seals. trying to understand the sealing mechanim in this kinda high pressure liquid seal. We have three seals. on a test pump middle seal have more wear than the first one and third one. What does that mean? First seal didnt energize? Can somebdy explain how these seals work. Please see the attachment for picture.

 

[MikeHalloran]

The picture is of a stepped joint backup ring, which is not a seal at all.
Its sole mission is to prevent an immediately adjacent seal from extruding itself between the piston and the cylinder.
The seal should be in the middle of the groove, surrounded by backup rings.

Consider the possibility that your pump is assembled incorrectly.




Mike Halloran
Pembroke Pines, FL, USA

 

[hydtools]

May be one like this?

http://www.allsealsinc.com/Piston-Rings.html

Or this one?

http://www.kolbenringindia.com/piston-ring-gaps.html

Or this one?

http://www.grovercorp.com/rings-and-seals/step-cut.html

If the middle seal is worn more, the outer two must be working well and the middle seal lacked lubrication, was very dry.

Ted

 

[raheeli]

Thanks for the replies. We use a energizer behind the seals. Seal material is UHMW. what i am trying to understand is the mechanism. Does all the seal energizes (unlikely becuase of pressure drop in the first ones). in case of gas yes but in liquids pressure drop across first seal should be big. I always thought first seal does the job first. when its warn out second seal takes over and then third. Thefore to increase pump life one way is to increase number of seals. but looks like its not that simple.

 

[Cockroach]

Actually, you expect the fist seal to leak a bit, metal-to-metal mating surfaces require high pressure to seal. So at lower pressures there is fluid bypass, which is used to energize the second, and so forth.

I have had your experiences a lot with Chevron Packing or vee seals. They are good at high pressures, but experience fluid bypass before their surfaces flex to energize. Sometimes I just put a soft seat I between the packing. Three up, o-ring then three down is my arrangement.

Maybe. You could do the same? Good luck with it.

Regards,
Cockroach

 

[hydtools]

If the first seal leaks at all the second seal will, in time depending on the first seal leak rate, see nearly full pressure. Nearly full pressure at the second seal because if it also leaks there will be leakage flow to the third seal. The intent is to provide a series of pressure drops or leakage flow resistance so that little or no leakage passes the seal series compared to a single seal.

Ted

 

[EdDanzer]

Without more application information one can only guess. What is your definition of high pressure?
Stepped rings leak through the steps in most cases it gets worse as the pressure expands the housing.
UHMW is possibly the worst material choice you could make for high pressure.

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com