I visited a neon sign shop today, to get some high voltage wire. I must say that this is a MUST DO activity for any neophite like me. This guy had a power line transformer (It was the size of two five gallon cans one on top of the other) hooked up in reverse to provide 30kv AC. The insulators were covered with four inch PVC pipe with an AC ammeter mounted in a T in one of the pipes. All of the vacuum connections were glass. He even had a hand blown glass diffusion pump.
Well anyway, he had a Welch 1400, with a ballast valve, and the valve was mounted in the LOWER hole and the valve inlet was BELOW the top of the oil.
I also drove into St. Paul to visit with a guy who rebuilds and sells vacuum pumps. He was a STRONG supporter of the use of the ballast valve to help keep the pump oil clean. He claimed that you can leave the pump running for about three days with the valve open and actually "refine" the pump oil. I bought a valve assembly from him for $10.00. The valve assembly is actually quite complex, the tip of the plunger is hinged on a small pin and has a ball at the very tip. The actual vent in the thumb screw head is drilled with a #42 drill (0.093 inch) hole, and there is a small spring loaded ball valve in the head. Probably to keep oil from leaking out if the pump is shut off with the valve open. I will post a picture of the valve here for a few days and then delete it to save server disk space.
The only thing I need now is the nipple. He told me that it has straignt threads on both ends, and I can make one by just drilling out a bolt and cutting off the head.
He also told me that to do a proper total rebuild on Welch pumps you need special jigs to get the proper clearences on the rotors and vanes, But replacing seals and gaskets should be no problem for the neophite.
When I asked him if he had any diffusion pumps, he replied "your in luck", then walked over to his garbage can and pulled out two used diffusion pumps and gave them to me with four ounces of Cambridg pump fluid!
I have some questions about the pumps, which I will post on a new thread.
Created on Friday, April 13, 2001 3:21 PM EDT by Thomas D Dressel Last Modified on Wednesday, April 18, 2001 11:35 AM EDT by Thomas D Dressel