On non-bonneted knife gate valves, multiple rows of packing material are placed around a gate and then compressed with a packing gland. This configuration forms a substantially liquid tight seal in order to hinder fluid leakage. Current packing glands are configured as a single piece structure that surrounds the gate. However, when a knife gate valve sized for a relatively large pipe is used, the packing area substantially increases. Further, typical manufacturing and assembly tolerances cause the geometry of a packing box to vary thus causing corresponding variations in packing height.
As a result, current packing glands have several disadvantages when used with relatively large valves. A disadvantage is that the packing gland has to be relatively large and structurally robust and heavy in order to be able to accommodate the increased size of the packing area and the forces required to suitably compress the packing material. In addition, the packing gland cannot be removed for maintenance operations, such as re-packing the valve, without disconnecting a valve actuator system. Further, the packing gland is not able to provide uniform pressure on the packing material if the packing height varies. In use, the packing material is compressed by tightening the packing gland until no leakage occurs. However, this leads to over tightening in some locations, thus reducing the life of the packing material and increasing valve thrust.
USPTO Backgrounds
USPTO Backgrounds