Gate valves, typically designed to be fully opened or closed, are primarily used to permit or prevent the flow of liquids with minimal pressure drop through the valve. There are four principal designs for gate valves, but all are characterized by having either a rising or a nonrising stem. It is helpful to consider stem construction when choosing the proper gate valve for your application.
Nonrising Stems - Inside Screw are threaded into the upper end of the gate. The wedge travels up and down the threads of the stem without any vertical movement of the handwheel or the stem. Nonrising stems are ideal for use underground or in applications where minimum clearance is required for its operation. Packing wear is also reduced due to the stem not traveling vertically. Care must be taken to protect the stem threads inside the valve from erosion, solids in the fluid, or excessive heat.
Rising Stems - Inside Screw are attached directly to the gate such that the wedge, handwheel, and stem rise and lower together as the valve is operated. The position of the disc or wedge inside the valve is easily indicated by the stem and handwheel position. This is a very common stem design and is readily found in bronze gate valves. Rising stem construction requires ample room for operation, so the amount of available clearance must be considered before selecting a rising stem gate valve. When a rising stem is in the open position the internal back seat protects the stem threads, but steps should be taken to protect the stem externally.
Rising Stems - Outside Screw and Yoke (OS&Y) are constructed to keep the stem threads outside the valve. As the handwheel is rotated, the yoke bushing engages the stem threads allowing the stem to rise while the handwheel remains in the same location. OS&Y construction is recommended for high temperature applications, or where corrosive liquids and liquids containing solid particles might damage stem threads located inside the valve. Another benefit to OS&Y construction is that the external threads make for easy lubrication. Care should be exercised to protect these external threads from damage. Keeping exposed valve stems clean and lubricated ensures ease of operation and prevents wear caused by dirt or rust. Minor precautions like these will save you time, money, and ensure the long life of the valve.
Milwaukee Valve is committed to quality and service. We welcome the opportunity to assist you in determining the valve most suited to your service conditions.
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