TYPES OF VALVESDOE-HDBK-1018/2-93ValvesIn a common, nonlubricated, plug valve having an elastomer sleeve, a sleeve of TFE completelysurrounds the plug. It is retained and locked in place by a metal body. This design results ina primary seal being maintained between the sleeve and the plug at all times regardless ofposition. The TFE sleeve is durable and inert to all but a few rarely encountered chemicals. Italso has a low coefficient of friction and is, therefore, self-lubricating.ManuallyOperatedPlugValveInstallationWhen installing plug valves, care should be taken to allow room for the operation of the handle,lever, or wrench. The manual operator is usually longer than the valve, and it rotates to aposition parallel to the pipe from a position 90 to the pipe.PlugValveGlandsThe gland of the plug valve is equivalent to the bonnet of a gate or globe valve. The glandsecures the stem assembly to the valve body. There are three general types of glands: singlegland, screwed gland, and bolted gland.To ensure a tight valve, the plug must be seated at all times. Gland adjustment should be kepttight enough to prevent the plug from becoming unseated and exposing the seating surfaces tothe live fluid. Care should be exercised to not overtighten the gland, which will result in ametal-to-metal contact between the body and the plug. Such a metal-to-metal contact creates anadditional force which will require extreme effort to operate the valve.DiaphragmValvesA diaphragm valve is a linear motion valve that is used to start, regulate, and stop fluid flow.The name is derived from its flexible disk, which mates with a seat located in the open area atthe top of the valve body to form a seal. A diaphragm valve is illustrated in Figure 14.Figure 14 Straight Through Diaphragm ValveME-04Rev. 0Page 24
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