MKS HPS LPV1-25-AC Series, Operation And Maintenance Manual

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Figure 3 - Limit switch operation
4.1.2 Limit Switch Actuation
When a valve is equipped with limit switches, they are mounted on top of
the cylinder as shown in Figure 3. When the valve is closed, the lever of the
closed position switch (18) is depressed by the cam extension (17) on the
top of the stem (6). When the valve is fully opened, the cam extension
activates the lever of the open position switch (16).
Observing that the closed position limit switch is actuated does not
necessarily verify that the valve is sealed leak tight, as contamination or
damage to the seal or seat could affect seal integrity. It does confirm,
however, that the valve, and its control, obeyed the command to move to
the closed position.