Agilent Technologies VPI Series, Instruction Manual

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Vacuum Pump Isolation (VPI) Valve
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2.3 Mechanical
The VPI valve is installed between the mechanical pump and vacuum chamber or high
vacuum pump (Figure 5). The flow arrows on the unit’s label point from the vacuum system
to the mechanical pump.
Figure 5 Installation Diagram
While it is preferable to mount it directly onto the mechanical pump, it may be located
remotely. For best performance, the maximum volume should be on the vacuum system
side, and the minimum volume on the mechanical pump side of the VPI valve. Operation is
position independent and standard ISO-KF centering ring assemblies and clamps are used to
connect the VPI valve. The valve body can operate in ambient temperatures up to 100° C,
but the solenoid is limited to about 50° C because of the heat generated by the coil. This
should be kept in mind when selecting a mounting location.
The body of the VPI valve is very rugged, and it is difficult to deform it in any normal piping
arrangement used in vacuum systems. It is possible, however, that tremendous forces could
result from thermal expansion or from a long run of pipe cantilevered from a fixed valve.
Where this possibility exists, provide stress relief for the valve by installing a short bellows
and support the attached piping other than with the valve.
Valves are shipped with plastic snap-on covers over the ports to protect the delicate seal
surfaces and to keep the valve clean. These covers should be left in place until the moment
when the valve is to be installed in the piping. A single fiber or bit of lint on an O-ring seal
is enough to prevent leak-tight sealing. The usual cleaning techniques in vacuum practice
should be observed in installing the valve.
When installing the valve, adequate clearance should be allowed between adjacent
components so there is no sliding of seal surfaces against each other. Flanges that have been
assembled for some time may stick together. They should be separated gently.
CAUTION
Don’t set the valve down on unprotected seal surfaces.