User manual

Instructions for Use
To Use as a Roughing Valve
1
Variable Leak Valve User Manual / 87-400-085-01 (D) 19/36
Bakeout in Closed Position
a The valve must be overdriven three turns past closure (normal
setting is two turns) to compensate for differential expansion of
materials during bakeout.
b To prepare the valve for bakeout, follow the procedure described
in para. “To establish a new stop position” with the following
exceptions: in steps 5 and 6, substitute "three turns" for the "two
turns" specified.
Operation After Bakeout
a Bakeout in the closed position to 250 °C and above will increase
the size of leak for a given setting of the knobs. A full three turns
may not be required to open a leak after bakeout. Length of
bakeout and elapsed time at temperature will both affect the
amount of change.
b If the stops are to be readjusted, follow the procedure described
in steps "a" and "b" above.
CAUTION!
After each bakeout cycle, before opening or closing the valve, tighten the outer
knob against the inner one and lubricate the threads of the fine drive screw
with Fel-Pro C-100. After every three bakeouts over 300°C, disassemble and
lubricate the drive mechanism as described in the following para. “Lubrication
instructions”.
To Use as a Roughing Valve
The variable leak valve can be used as a roughing valve when
pumping small vacuum systems (some litres volume). The valve must
be opened to its maximum conductance for this operation.
Connect a roughing pump to the inlet gas fitting. Where available,
install a molecular sieve or liquid nitrogen trap in the line between
the pump and valve to reduce contamination from mechanical pump
oil vapours.