Thermal binding is a very serious phenomenon, which can cause a wedge gate valve to become jammed in the closed position. It has two primary causes:
- A relatively cool valve stem is inserted into a hot valve. After closing on torque, the stem then warms up and grows further increasing the seating force.
- As the valve body cools down, the seats contract on the valve wedges, locking them in place.
The reason a wedge gate valve can become thermally locked under either of these conditions is its seating method, which requires wedging the disc into the body. Since the disc is wedged into the valve body it cannot compensate for varying rates of contraction between the large valve body and smaller disc or for the stem growth of a cool stem. This results in an increased amount of torque being required to break the disc away from its seat. The higher required torque can result in either an insufficient amount of torque being available to open the valve or in an over torque of the valve stem disc connection resulting in failure of that connection.
Since our Parallel Slide Gate Valve uses a position-seating method, its design offers protection against thermal binding of a wedge gate valve in the closed position. If a relatively cool valve stem grows after insertion into a hot valve, the growth only moves the discs down slightly, with the seats remaining in firm contact with each other. This prevents an increase in the torque requirement to open the valve.
When a hot valve is closed if the valve body cools, and contracts faster than the valve disc, the body will squeeze in on the discs. The spring between the discs will then compress slightly, allowing the sealing force to remain constant, preventing thermal binding from occurring.
Thus the Parallel Slide Gate Valve with its position-seated design protects against thermal binding.