TYPES OF VALVESDOE-HDBK-1018/2-93ValvesNon-variable reducing valves eliminate the need for the intermediate auxiliary valve found invariable reducing valves by having the opposing forces react directly on the diaphragm.Therefore, non-variable reducing valves are more responsive to large pressure variations and areless susceptible to failure than are variable reducing valves. PinchValvesThe relatively inexpensive pinch valve,Figure 18 Pinch Valvesillustrated in Figure 18, is the simplestin any valve design. It is simply anindustrial version of the pinch cockused in the laboratory to control theflow of fluids through rubber tubing.Pinch valves are suitable for on-offand throttling services. However, theeffective throttling range is usuallybetween 10% and 95% of the ratedflow capacity.Pinch valves are ideally suited for thehandling of slurries, liquids with largeamounts of suspended solids, andsystems that convey solidspneumatically. Because the operatingmechanism is completely isolated fromthe fluid, these valves also findapplication where corrosion or metalcontamination of the fluid might be aproblem.The pinch control valve consists of a sleeve molded of rubber or other synthetic material anda pinching mechanism. All of the operating portions are completely external to the valve. Themolded sleeve is referred to as the valve body.Pinch valve bodies are manufactured of natural and synthetic rubbers and plastics which havegood abrasion resistance properties. These properties permit little damage to the valve sleeve,thereby providing virtually unimpeded flow. Sleeves are available with either extended hubs andclamps designed to slip over a pipe end, or with a flanged end having standard dimensions.ME-04Rev.0Page 30
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