| ▲ Vacuum |
I eventually decided to try and make a proper, leak-proof manifold for the vacuum pump so I can evacuate a system and fill it to any desired pressure with gas. The photos below show what I ended up with.
The pump is a 2-stage Alcatel unit. The pump isolation valve (brass with the black knob) is oriented so the stem packing is on the vacuum pump side, not the system side, so any leaks are taken care of. After that, the rest of the pipework uses VCR connections with aluminium gaskets, because I had a box of miscellaneous VCR stuff. Coming in from the left is the gas inlet, through a stainless Nupro needle valve. Again, the stem packing is on the gas side, not the vacuum side.
On the right we have a pressure gauge and the connection to the device to be evacuated. The gauge is just a -1 to +2 bar dial gauge, and is really just to tell me whether the system is at vacuum or atmosphere. Fine control of the pressure is done looking at a glow discharge in the device. Interestingly, the first vacuum gauges I tried actually leaked! The connection to the device is with a little O-ring gland - I made it to fit a 6mm glass tube, since most of the things I'll be making will have that on them.
It works beautifully, and is completely leak-free. The pump can actually take the pressure down so far that a discharge can't be obtained and, even if the valves are shut, the pressure remains this low showing there are no leaks.
 Overall view |
 Gas inlet via needle valve on left. Pump valve at bottom. To system on right. |
 Vacuum gauge on left, system connection on right. |
 Gland for 6mm glass tubing. |
24/02/11 New knob. Put a better, bigger knob on the vacuum valve. Had to make a little extension bit since the existing valve stem was so short. Now it's really solid!
 Closeup of knob |
| ▲ Vacuum |