ValvesDOE-HDBK-1018/2-93TYPES OF VALVESGlobeValvesFigure 9 Z-Body Globe ValveA globe valve is a linear motion valveused to stop, start, and regulate fluid flow.A Z-body globe valve is illustrated inFigure 9.As shown in Figure 9, the globe valvedisk can be totally removed from theflowpath or it can completely close theflowpath. The essential principle of globevalve operation is the perpendicularmovement of the disk away from the seat.This causes the annular space between thedisk and seat ring to gradually close as thevalve is closed. This characteristic givesthe globe valve good throttling ability,which permits its use in regulating flow.Therefore, the globe valve may be usedfor both stopping and starting fluid flowand for regulating flow.When compared to a gate valve, a globevalve generally yields much less seatleakage. This is because the disk-to-seatring contact is more at right angles, whichpermits the force of closing to tightly seatthe disk.Globe valves can be arranged so that the disk closes against or in the same direction of fluidflow. When the disk closes against the direction of flow, the kinetic energy of the fluid impedesclosing but aids opening of the valve. When the disk closes in the same direction of flow, thekinetic energy of the fluid aids closing but impedes opening. This characteristic is preferableto other designs when quick-acting stop valves are necessary.Globe valves also have drawbacks. The most evident shortcoming of the simple globe valve isthe high head loss from two or more right angle turns of flowing fluid. Obstructions anddiscontinuities in the flowpath lead to head loss. In a large high pressure line, the fluid dynamiceffects from pulsations, impacts, and pressure drops can damage trim, stem packing, andactuators. In addition, large valve sizes require considerable power to operate and are especiallynoisy in high pressure applications.Other drawbacks of globe valves are the large openings necessary for disk assembly, heavierweight than other valves of the same flow rating, and the cantilevered mounting of the disk tothe stem. Rev. 0ME-04Page 15
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