I have my rudimentary vacuum system in operation. It is a Welch 1400, connected to a Hastings KF25 pneumatic valve, connected to a micromaze, connected to a Hastings KF15 pneumatic Valve,connected to a vacuum chamber. I have rigged it so that the valves are controlled by solenoids. If there is a loss of power they close automatically.
The chamber consists of an aluminium base plate (with four of its original holes potted closed), 6 inch OD, 1/2 inch thick, 8 inch long cast plexiglass tube with O-Ring grooves in each end and a one inch thick plexiglas disk for a cover. I also have connections in the base plate for a TC vacuum guage and Nupron pneumatic valve connected to a Nupron needle valve, (all cajon fittings) for venting the chamber or eventually bleeding in D2.
The problem is that although the Welch 1400 is good for 20 to 25 microns at the pump head, when the valve to the chamber is open, the pressure increases to 45 to 50 microns as measured in the chamber and the pump head. This is after a good micromaze bakeout and pumping all weekend. The foreline pressure will go down to 25 microns and the chamber pressure will rise five to ten microns per minute, up to about 500 microns, with the chamber valve closed. I assume that this is due to outgassing of the plexiglass and potting material used to close off some holes in the base plate. Is this type of virtual leak the sort of thing that lasts forever, (or until all the potting material and plexiglass are vaporized), or can I expect it to improve with time?
I have looked at Richard Hester's fusor budget for the vacuum chamber v.1 and v.2.
On Friday, I fixed a few cut finger tendons on a guy who owns a custom bike frame shop in Minneapolis. He can do the machining and TIG welding for me (when the cast on his hand comes off), if I decide to go stainless all the way. I have all the fittings except the 2.75" conflat viewport, hemispheres, weld flanges, claw clamps, and centering ring. I would like to build a 6" chamber (Parts cost $354.90), or 8" chamber (Parts cost $492.90), with as few welds in it as possible. A KF25 port for pumpdown, KF25 for high voltage feed through and 2.75" conflat for a combined viewport, TC guage port, and gas bleed port (I have a 3/4" inch thick 2.75" conflat spacer block with 1/8" NPT and 1/4" NPT tapped holes in the side). I also have the KF16 nipples for individual ports (all this stuff came with the Hummer V package). The question is, does anyone see a problem with having a viewport, pressure tap and gas bleed that close together in one port? Or should I go with individual ports?
Created on Sunday, April 08, 2001 5:18 PM EDT by Thomas D Dressel