I have posted complete details on this in the old BBS.
The two valves act to isolate the maze. These valves are always fully closed if the pump is not on!
When first pumping or renewing a pump down, the valve closest to the mechanical pump (between pump and maze) is opened once the fore line is in transition or molecular flow. let this run a bit to pump out the maze for 60 seconds or so.
Next open the valve between the maze and the fusor.
Now when shuting the pump down, but while it is still running, reclose the valve between fusor and the maze. finally reclose the foreline valve. Turn off the pump and let the foreline up to air. This way, the maze is isolated, pumped down and will remain dry and safe, until next pump down cycle.
to bake out with internal maze heater........
start mechanical pump and open the gas ballast wide open and leave it open for the entire bake out with the pump never stopping. turn on the internal maze heater. pump until the maze has been thoroughly baked out (often 3 hours). Also make sure the oil in the pump is clean through the sight glass.
If all the above conditions are met, then turn off the heater and walk away with the pump still on. after the maze has cooled for about 1 hour, return and shut the foreline valve. Isolating the maze once again. Close the mechanical pump's gas ballast, turn off the pump and let the foreline up to air and you are done. This can take an entire afternoon and leave yourpump motor red hot!!
Notice that during the entire bakeout we never,ever touched or opened the maze to fusor isolation valve.
Richard Hull
Created on Friday, March 16, 2001 1:39 PM EDT by Richard Hull