ValvesDOE-HDBK-1018/2-93TYPES OF VALVESSolidWedgeFigure 5 Solid Wedge Gate ValveThe solid wedge gate valve shown in Figure 5 is the mostcommonly used disk because of its simplicity and strength.A valve with this type of wedge may be installed in anyposition and it is suitable for almost all fluids. It is practicalfor turbulent flow.FlexibleWedgeThe flexible wedge gate valve illustrated in Figure 6 is aone-piece disk with a cut around the perimeter to improvethe ability to match error or change in the angle between theseats. The cut varies in size, shape, and depth. A shallow,narrow cut gives little flexibility but retains strength. Adeeper and wider cut, or cast-in recess, leaves little materialat the center, which allows more flexibility but compromisesstrength.A correct profile of the disk half in theFigure 6 Flexible Wedge Gate Valveflexible wedge design can give uniformdeflection properties at the disk edge,so that the wedging force applied inseating will force the disk seatingsurface uniformly and tightly against the seat.Gate valves used in steam systems have flexible wedges. Thereason for using a flexible gate is to prevent binding of the gatewithin the valve when the valve is in the closed position. Whensteam lines are heated, they expand and cause some distortion ofvalve bodies. If a solid gate fits snugly between the seat of a valvein a cold steam system, when the system is heated and pipeselongate, the seats will compress against the gate and clamp thevalve shut. This problem is overcome by using a flexible gate,whose design allows the gate to flex as the valve seat compresses it.The major problem associated with flexible gates is that water tendsto collect in the body neck. Under certain conditions, the admissionof steam may cause the valve body neck to rupture, the bonnet to liftoff, or the seat ring to collapse. Following correct warmingprocedures prevent these problems.Rev. 0ME-04Page 11
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