Abstract: An improvement in an apparatus for carrying out chemical reactions is disclosed. The apparatus includes a housing defining a vacuum chamber, with a reactor located within the vacuum chamber. The improvement comprises a device disposed within the housing having a high-pressure outlet tube for engagement with the reactor, a bypass for placing the high-pressure outlet tube in fluid communication with the outside of the vacuum chamber, an orifice for placing the high-pressure outlet tube in fluid communication with the vacuum chamber and at least one valve for selectively opening or closing the bypass and the orifice. The device may be engaged and disengaged with the reactor by a manual shaft and gear arrangement for operating the reactor at higher pressures relative to the normal vacuum operation.