Loop seal for knife gate valve

#This invention relates to seals used in valves to control fluid flow and especially to seals useable in knife gate valves.

#Knife gate valves are useful in a wide variety of fluid control applications, for example, in the petroleum and chemical industries, mining, power generation, as well as municipal and industrial water service utilities, wherever there is a need for a valve with a high flow capacity and relatively low head loss to control flows which need not be throttled.

#Knife gate valves are generally understood as comprising a housing, which permits the valve to be positioned in a fluid conduit line, and a movable valve member in the form of a flat plate (the knife gate) that is slidably movable within the housing. The gate is movable transversely to the fluid flow direction between an open position, wherein the gate is removed from the fluid flow path through the housing to allow fluid flow through the valve, and a closed position, wherein the gate is inserted into the fluid flow path to block the fluid flow.

#FIG. 1 is a perspective view of a knife gate valve seal according to the invention;

#FIG. 2 is a cross-sectional view taken at line 2—2 of FIG. 1;

#FIG. 3 is an elevational longitudinal perspective sectional view of a knife gate valve using a seal according to the invention;

#FIG. 1 shows a seal 10 according to the invention. Seal 10 comprises a flexible resilient loop 12 that defines a central bore 14. Loop 12 is preferably substantially circular in shape, but could also be oval, ellipsoidal, polygonal or any other shape defining a closed loop. The loop comprises a flexible, resilient sealing lobe 16 which extends around it. Sealing lobe 16 has a deformable sealing surface 18 that faces in an axial direction as defined by an axis 20 defining a flow path through bore 14 of loop 12. Sealing surface 18 comprises a leading edge 22 projecting in the axial direction. Annular sealing surfaces 24 and 26 extend from the leading edge 22, sealing surface 24 extending inwardly of loop 12 and sealing surface 26 extending outwardly of the loop. Annular sealing surfaces 24 and 26 are preferably angularly oriented with respect to the leading edge 22 for reasons explained below. Preferably, the annular sealing surfaces are substantially flat although other configurations are feasible.

#Loop 12 also has an outwardly facing perimeteral surface 28 in which one or more flat regions 30 are positioned. The flat regions 30 of surface 28 are preferably positioned diametrically opposed from one another and are oriented substantially parallel to respective chord lines 32 through the loop 12. The flat regions 30 are engageable with complementary flat surfaces within a knife gate valve in which the seal 10 is mounted to orient the loop relative to the valve. Such flats provide the advantage of a more compact valve.

#As best shown in FIG. 2, an axially facing channel 34 (called the “axial channel”) is positioned within loop 12 axially opposite to the sealing lobe 16. Axial channel 34 extends around loop 12 and faces away from the sealing lobe 16. Another channel 36, known as the “inner channel”, is positioned adjacent to the sealing lobe 16 and also extends around the loop 12. Inner channel 36 faces inwardly toward the axis 20. Together, the axial and inner channels 34 and 36 provide a free space into which the loop 12 may deform when the sealing lobe 16 is compressed when installed in a knife gate valve and performing its sealing function.