Wp120210b Integral Seats Vs Alloy Seats

Integral Seats

/ Copeland »
Design Considerations /

WP120210b Integral Seats vs Alloy Seats

Definition

A flow control orifice and seat that is an integral part of the valve body or cage. The seat is machined directly out of the valve body and is not replaceable without replacing or repairing the body itself.

Advantage

There is no chance of leakage behind a seat. Non-integral seated valves may use a locking device with a mate lapped seal to lock the body into place with excellent success. The main advantage is an economic one that allows the manufacturer to avoid the expense making a separate seat and locking device.

Disadvantages

When the valve body or end connection needs to be repaired, a whole body must be replaced or repaired instead of one ring. Tolerance concessions are normally made to account for variences in coating thicknesses in manufacturing an integral seated valve. The biggest issue for high temperature valves is the possibility of the the ball and body loosing a seal because the body is made of a dissimilar material and expands at a different rate. Manufacturer bench tests will not detect this issue because most bench tests are performed at ambient temperatures. This problem is made worse when the internals are materials like 316ss that expand and contract much faster than, say, a carbon steel body will.

Alloy Seats

Ball valves made with non-integral seats typically match the seat material to the ball material so that both will expand and contract together. A locking device is recommended when back pressure is a possibility so that material does not get behind the downstream seat and ruin the seal. Alloy seats are the best assurance of maintaining tight seals when temperature is an issue.

Copeland Industries, Inc. / 6841 Ave. U, Houston, Texas 77011 / 713-926-7481