Discussion on triple offset valve 2

A triple offset valve is a rotary, butterfly-style valve. A standard butterfly has no offset: THe shaft and vane are coincident with the centerline of the pipe. A double-offset butterfly has the shaft offset back from the centerline of the seating surface, and offset to one side of the centerline. This helops the disc "cam" into the seat but the seat must still be resilient to accept the edge of the vane in the last degrees of seating.

A triple-offset valve is like a double-offset, with the addition that the edge of the seating surface is generated as the surface of a cone, which itself is offset so that one of its sides is parallel to the wall of the pipe. This makes the seating surface slightly elliptical, but it meets the seat without needing to be distorted. Metal seats are possible, eliminating the limitations of elastomer seats. A slightly flexible laminated stainless/graphite seat seal is used to conform to the small irregularities in the seating surfaces, but the seating torque is necessarily high.Triple offset valves can survive higher temperatures and higher pressures than other types.

This forum does not support pictures so I imagine you are well confused by this at this point. A diagram will help.

Tyco Keystone Vanessa and Adams Tricentric are prominent triple-offset valves.

Thanks JimCasey,

I know the picture that you mention. I just am doing some research on triple offset. It seems it is great compared with double offset. But, I know some tripe offsets are not bubble-tight? Why? Their torque is not strong enough? Are you the designer in the butterfly valve. You are so powerful and knowlegable. Thanks.

SamHui,
if you want to display the products mentioned by JimCasey, take a look at the following web-pages (more links and information on Thread408-64692 within this Forum...):



In addition, you can find a tipycal scheme explaining the tripple-offset principle in page 5 of the .pdf document at the address:

About design philosophy and seating mechanism, it must be noticed that some Manufacturers use the seal on the seat (i.e. integral to the valve body), some Others put the seal (the above mentione lamellar seal ring in steel and graphite) on the rotating disc.

Depending on the application, of course, good tightness performances can also be reached with a proper selection of design parameters, materials and torques to apply (may be the major problem is unseating, more than seating, sometimes...!).

Hope this helps, 'NGL