User manual

Instructions for Use
To Set Stop Position at any Leak Rate
1
Variable Leak Valve User Manual / 87-400-085-01 (D) 17/36
To Set Stop Position at any Leak Rate
The stop position can be adjusted to provide any desired leak rate.
1. Open the valve to the desired leak rate as determined by a leak
detector, vacuum gauge, or other experimental means.
2. Loosen the knobs from each other without allowing the fine-drive
screw to turn.
3. Turn the inner knob clockwise until the collar stops against the
handle. Turn the outer knob clockwise until it locks against the
inner knob.
4. The valve can now be opened to larger leak rates and when
returned to the stop position will provide a leak of this pre-set
rate.
NOTE
The valve cannot be closed leak-tight with the stop set in this manner. To close
the valve, follow the procedure outlined in the preceding paragraph.
Operating at Low Leak Rates
When the valve operates with leak rates of 1 x 10
-9
Torr-litres/sec and smaller, condensable vapours and contaminants
reduce the leak opening. The valve must be baked to 250° in the open
position and under vacuum for 30 minutes to drive off these
internally adsorbed vapours. See the paragraph "Bakeout procedure".
For operation at leak rates of 3 x 10
-10
Torr-litres/sec and lower, in
addition to the bakeout described above, the inlet gas must be free of
condensable vapours. Use a dry gas or pass the inlet gas through a
drying agent such as a liquid nitrogen cold trap. A molecular sieve
trap can be used for drying the gas but a filter must be employed to
assure that no particles of sieve enter the valve.