Vacuum cut-off valve

Claim 1

A vacuum cut-off which comprises: a body member member having an inlet port for connection to a vacuum source, an outlet port for connection to a vacuum utilization device, and an air port connected to a source of atmospheric pressure; a flexible diaphragm for dividing the interior of said body member into a first chamber communicating with said outlet port and a second chamber communicating with said air port; first valve means for controlling fluid communication between said inlet port and said first chamber by the movement of said diaphragm; second valve means for controlling fluid communication between said first chamber and said second chamber by the movement of said diaphragm; a pipe associated with said inlet port and provided with a tip end acting as a first seat of said first valve means; a pressure plate made integral with said diaphragm and provided with a projection acting as a second seat of said second valve means and an axial hole within which said pipe is coaxially disposed wherein said pressure plate is provided with a small air chamber continuously communicated to said second chamber through an orifice passageway formed in said air chamber; and regulating means located in said first chamber and operatively connected to said diaphragm whereby said first valve is kept open while said second valve is kept closed before the inlet vacuum reaches a predetermined level, said diaphragm being movable due to the increase of the inlet vacuum whereby said first valve is closed when the inlet vacuum reaches the predetermined level, wherein said second valve is opened when vacuum in said second chamber increases above the predetermined level.