 |
Double Disc Wedge
In this design the “disc” actually consists of two separate solid discs which are positioned opposite to each other. The disc pair, however, works together. During the valve closure action, the last turn of the handwheel forces the discs apart and forces against the valve seats.
On the other hand, when you are opening the valve, the first opening turn releases the discs and they move slightly away from the valve seat. Once the discs are released, they can be pulled out as the stem moves upward.
There is a very important message in what we’ve been talking about so far. The moving parts in a valve are finely machined components and it is very easy to abuse them. For example, if you continue to apply excessive force after the valve is fully closed, you are liable to permanently damage the valve discs and valve seats. Unfortunately, this is a very common problem. Badly trained operators keep on using excessive force after the valve is fully closed, sometimes they use crowbars in this effort. They do this as a well-meaning gesture to ensure the valve is fully closed.