Juryrigging a Vacuum Controller

07 May 2016 at 13:04

Rotary evaporator setups can get fairly expensive fairly quickly. While a benchtop rotary evaporator itself can be a relatively inexpensive device (at least as far as lab equipment goes), a complete setup may require additional glassware, a vacuum pump, vacuum controller, and water chiller. When all these items are included, the cost can easily double or triple.

LabTech VC1000 Vacuum Controller

 

Vacuum controllers can be an expensive component in a benchtop rotary evaporator setup, yet if using a vacuum pump, use of a vacuum controller is critical. Without it, there is no control over vacuum pressure and therefore no control of the solvent boiling point, which is generally the whole point of applying a vacuum in the first place. Without a vacuum controller, you'll end up at the pump's minimum pressure, which may leave you with a solvent boiling point near or below room temperature, especially for volatile solvents with already low boiling points at standard atmospheric pressure. While manual vacuum regulators are less expensive than electronic ones, even they can still cost over $500.

Luckily, a vacuum controller is something that you can juryrig with a number of relatively available parts and a bit of plumbing. You can easily do it for under $100.

Hook up your pump to a T-fitting, with one line going to the condenser (with the pressure gauge on that line) and the other to the ambient environment. The line to the ambient air should have a good quality shutoff valve that allows fairly fine control. With a "dry" run using only solvent, run the system as you normally would with the valve open. Turn on the vacuum pump and then very slowly close the shutoff valve until you start pulling less and less air. Stop when you reach your desired pressure. Bingo - you now have a system running at your desired pressure, and you've just built your own rudimentary vacuum controller!


Schematic of juryrigged vacuum controller. The pressure gauge may be connected inline or via a second T-fitting.