TYPES OF VALVESDOE-HDBK-1018/2-93ValvesNeedleValveBodyDesignsOne type of body design for a needle valve is the bar stock body. Bar stock bodies arecommon, and, in globe types, a ball swiveling in the stem provides the necessary rotation forseating without damage. The bar stock body is illustrated in Figure 21.Figure 21 Bar-Stock Instrument ValveNeedle valves are frequently used as metering valves. Metering valves are used for extremelyfine flow control. The thin disk or orifice allows for linear flow characteristics. Therefore, thenumber of handwheel turns can be directly correlated to the amount of flow. A typical meteringvalve has a stem with 40 threads per inch. Needle valves generally use one of two styles of stem packing: an O-ring with TFE backingrings or a TFE packing cylinder. Needle valves are often equipped with replaceable seats forease of maintenance.ME-04Rev.0Page 34
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