Figure 6-6.—Types of globe valve bodies.from the globular shape of the valve body. Othertypes of valves may also have globular-shapedbodies. Thus, it is the internal structure of thevalve that identifies the type of valve.The inlet and outlet openings for globe valvesare arranged in a way to satisfy the flowrequirements. Figure 6-6 shows straight-, angle-,and cross-flow valves.The moving parts of a globe valve consist ofthe disk, the valve stem, and the handwheel. Thestem connects the handwheel and the disk. It isthreaded and fits into the threads in the valvebonnet.The part of the globe valve that controls flowis the disk, which is attached to the valve stem.(Disks are available in various designs.) The valveis closed by turning the valve stem in until the diskis seated into the valve seat. This prevents fluidfrom flowing through the valve (fig. 6-7, view A).The edge of the disk and the seat are veryaccurately machined so that they forma tight sealwhen the valve is closed. When the valve is open(fig. 6-7, view B), the fluid flows through the spacebetween the edge of the disk and the seat. Sincethe fluid flows equally on all sides of the centerof support when the valve is open, there is nounbalanced pressure on the disk to cause unevenwear. The rate at which fluid flows through thevalve is regulated by the position of the disk inrelation to the seat. The valve is commonly usedas a fully open or fully closed valve, but it maybe used as a throttle valve. However, since theseating surface is a relatively large area, it is notsuitable as a throttle valve, where fine adjustmentsare required in controlling the rate of flow.The globe valve should never be jammed inthe open position. After a valve is fully opened,the handwheel should be turned toward the closedposition approximately one-half turn. Unless thisis done, the valve is likely to seize in the openposition, making it difficult, if not impossible, toclose the valve. Many valves are damaged in thisFigure 6-7.—Operation of a globe valve.6-4
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