Samson 3251 Mounting And Operating Instructions

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Samson 3251 Mounting And Operating Instructions Manual pdf 14 page image

14 EB 8052 ENDesign and principle of operation3 Design and principle of oper-ationThe single-seated Type 3251 Globe Valve ispreferably combined with a SAMSONType 3271 or Type 3277 Pneumatic Actuator(see Fig. 3). It can also be combined withother actuators.The seat (4) and plug with plug stem (5) areinstalled in the body (1). The plug stem isconnected to the actuator stem (A7) by thestem connector clamps (A26) and is sealedby a spring-loaded V-ring packing (15). Thesprings in the pneumatic actuator (A) are lo-cated either above or below the diaphragm(A4) depending on the selected fail-safe ac-tion (see section 3.1). A change in the signalpressure acting on the diaphragm causes theplug to move. The actuator size is deter-mined by the diaphragm area.The medium flows through the valve in thedirection indicated by the arrow. A rise insignal pressure causes the force acting onthe diaphragm in the actuator to increase.The springs are compressed. Depending onthe selected direction of action, the actuatorstem retracts or extends. As a result, the plugposition in the seat changes and determinesthe flow rate through the valve.3.1 Fail-safe positionsThe fail-safe position depends on the mount-ed actuator.Depending on how the compression springsare arranged in the pneumatic actuator, thevalve has two different fail-safe positions:Actuator stem extends (FA)When the signal pressure is reduced or theair supply fails, the springs move the actua-tor stem downward and close the valve. Thevalve opens when the signal pressure is in-creased enough to overcome the force exert-ed by the springs.Actuator stem retracts (FE)When the signal pressure is reduced or theair supply fails, the springs move the actua-tor stem upwards and open the valve. Thevalve closes when the signal pressure is in-creased enough to overcome the force exert-ed by the springs.The actuator's direction of action can be re-versed, if required. Refer to the mountingand operating instructions of the pneumaticactuator:u EB 8310‑X for Type 3271 and Type 3277Tip