[beheada]

So I have a vacuum distillation set up using an actual rotary vane pump, yet the vacuum is designed for physics experiments at extremely low atmosphere. I'm trying to figure out a way to put in a valve from the pump to the water trap (or after the water trap?) so that I can adjust the vacuum, but it seems if I expose the line to the outside atmosphere, that I lose the vacuum in the system? Do I need a variable pressure regulator (if they make such a thing?) Any suggestions on how this could be accomplished would be great.

[hmx9123]

Not exactly sure how your pump is set up, but many of them have a ballast you can open, thus bleeding in atmosphere and dropping your vacuum enough to be useable.  One of our rotovap pumps is so good that we have to crank the ballast open when we use it or it will *Ignore me, I am impatient* even high-boiling solvents like toluene.

[beheada]

Well... I've solved the problem. For anyone else who uses a vacuum pump which creates too little pressure in the system, simply attach any type of plumbing valve that will open slightly to atmosphere as a method of decreasing the vacuum pressure. I took hose adapters and threaded them to a three-way adapter, then atop the T of the adapter I attached a throttle valve (it's like a valve with a knob which adjusts the opening). You can probably use any valve as long as it doesn't open TOO much. What I'm ideally looking for, since I know this works, is a valve that "clicks" and locks into place at its various positions so that I can record the vacuum pull of each position by recording the BP of water in it and gauge the pull of each position.

Thanks for the response HMX

[hmx9123]

That's generally how a rotovap works--there's a stopcock that you can slowly open to bleed in atmospheric pressure.  It's kind of crude, but it does work.  Glad to hear it works for your purposes.