MKS HPS Two-Stage Manual De Servicio página 19

Disassembly of the bypass valve Chapter Two: Servicing an HPS Products Two-Stage
Valve
4-Unscrew piston nut while holding the spanner on the nosepiece. Remove the piston nut, warning
washer, piston, and the piston bushing. Inspect the piston U-cup and Teflon wear ring for excessive
wear.
5-Relax the puller, allowing the closing spring to expand. Hold onto the assembly to prevent its
falling from the puller when the spring is fully relaxed.
6-Remove the bellows assembly from puller. Withdraw the stem guide, closing spring, and spring
bushing.
7-Inspect stem for wear. Slight abrasion of the stem is acceptable as it will not cause failure of the
U-cup stem seal.
8-The bellows assembly can be leak tested while outside the valve, but care must be taken to limit
the compression of the bellows from atmospheric load.
9-To disassemble the upper stem guide assembly, 1) remove the two 6-32 x 0.25 pan head screws,
2) remove the seal retainer, 3) remove the stem seal. Inspect for wear.
Disassembly of the bypass valve
1-Vent both sides of valve
2-Turn off electrical power to the valve
3-Disconnect the air supply to the valve
4-Remove the four screws holding the actuator cap to the body flange. Note the position of the
micrometer head (if so equipped) so it can be replaced in the same orientation.
5-The actuator cap, compression spring, outer Ultem spacer, and internal assembly are now free to
be removed from the valve body. Contaminant buildup may stop the assembly from sliding out
easily. Care should be taken not to dent the bellows when pulling the internal assembly away from
the body. The actuator seal and bonnet seal O-rings may also be loose and should be removed.
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