Movable end plate for a vacuum pump

In a pump having a housing with an operational cavity therein, a rotor having vanes located in the operational cavity and an input member for moving the rotor in said cavity to move a fluid from an inlet port to an outlet port through the cavity and thereby to create a fluid pressure differential between the inlet port and the outlet port, the improvement comprising:

• by-pass means for connecting the outlet port to the inlet port when the fluid pressure differential reaches a predetermined level to substantially reduce the resistance to movement of the rotor in the operational cavity;
• a control cavity located in the housing;
• an end plate located in said housing to separate the control cavity into a by-pass chamber and a control chamber, said by-pass chamber being connected to a series of chambers between the vanes, and said control chamber being connected to said inlet port;
• and
• first resilient means located in said control cavity for urging said end plate toward the vanes to attenuate fluid communication through said by-pass chamber, said fluid pressure differential acting across said end plate and overcoming said first resilient means when the predetermined level is reached to move the end plate and allow communication from the inlet port to the outlet port through the by-pass chamber;
• a diaphragm for separating the control chamber from a sensing chamber, said sensing chamber being connected to said inlet port and said control chamber, said control chamber being connected to said surrounding environment;
• a valve carried by said diaphragm having a poppet assembly therein for controlling communication between said control chamber and said sensing chamber;
• and
• second resilient means located in said sensing chamber urging said diaphragm toward the control chamber, said diaphragm responding to a sensed pressure differential created by air from the environment on one side of the diaphragm and the fluid pressure at the inlet port in the sensing chamber by overcoming said second resilient means to move said valve to interrupt fluid communication between the control chamber and the surrounding environment while initiating fluid communication between said sensing chamber and the control chamber to develop said fluid pressure differential across said end plate.