Seats may be machined into the body, hardfaced with a cobalt or nickel alloy, threaded or welded in as a renewable ring, or made of a polymer such as PTFE, reinforced PTFE or PEEK in soft-seated valves. Seat condition decides shutoff tightness, and seat leakage is measured against a class or an allowable rate during the seat test. In ball valves, the seats are separate rings that the ball rotates against.
We lapped the seat on that globe and it's still passing, the steam cut must be too deep to lap out.
Also heard as
- seat ring
- valve seat
Related terms
Disc
The movable closure element that seats to stop flow in globe, check, safety and butterfly valves.
Wedge
The tapered closure member of a gate valve that is driven down between two inclined seats to seal.
Shutoff class
A rating of how much seat leakage a closed control valve is allowed, from Class I to Class VI.
Wire drawing
Erosion of thin grooves across a valve seat by a high-velocity jet leaking through a tiny gap.
Passing
Leaking through the seat while closed, so fluid still gets past a valve that is supposed to be shut.