can you please help me to understand what is thr meaning of "Impact Type Handwheel" for gate valves.An impactor handwheel has a crossarm that is directly coupled to the valve stem. The handwheel pushes against the crossarm to apply the torque. After the valve has been closed to a hand-tight position, the handwheel is backed off a bit (< 1/2 turn) but the crossarm stays in position (i.e. valve remains hand-tight). The handwheel is then spun quickly in the closing direction so that is 'impacts' the crossarm providing the much higher torque required to properly seat the valve. In large or high pressure valves, it may take several men to apply the torque required with a standard handwheel. With the impactor handwheel, the instantaneous torque applied when the handwheel strikes the crossarm can be as much 10 times greater (4000-5000 ft-lbf) than one person could apply with a standard handwheel.

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