Two stage scroll vacuum pump with improved pressure ratio and performance

A scroll vacuum pump having:

• a first stage including a first stage fixed plate having a spiral involute, a first stage orbiting plate having a spiral involute wrap, a first stage inlet, and a first stage outlet;
• said spiral involute wraps meshing with each other to define chambers, said chambers increasing in size from said first stage inlet to said first stage outlet;
• said first stage having an expansion ratio greater than or equal to one;
• a second stage including a second stage fixed plate having a spiral involute wrap, a second stage orbiting plate having a spiral involute, a second stage inlet in fluid communication with said first stage outlet, and a second stage outlet;
• said second stage spiral involute wraps meshing with each other to define chambers, said chambers decreasing in size from said second stage inlet to said second stage outlet;
• and said second stage having a compression ratio greater than or equal to one;
• an upper housing;
• said upper housing having an end surface spaced from said second stage fixed plate to define an exit chamber;
• said second stage exit being in fluid communication with said exit chamber;
• said upper housing including an outlet from said exit chamber;
• and
• a motor which drives said orbiting involute wraps;
• said motor being mounted to an outer surface of said upper housing and including an output shaft which extend through said exit chamber and said second stage fixed plate;
• said first and second stage orbiting scroll plates being operatively connected to said output shaft to be driven thereby;
• said output shaft being at atmospheric pressure;
• said scroll vacuum pump lacking any sealing which would seal said shaft from ambient atmosphere.

A scroll vacuum pump having:

• a first stage including a first stage fixed plate having a spiral involute, a first stage orbiting plate having a spiral involute wrap, a first stage inlet, and a first stage outlet;
• said spiral involute wraps meshing with each other to define chambers, said chambers increasing in size from said first stage inlet to said first stage outlet;
• and
• a second stage including a second stage fixed plate having a spiral involute wrap, a second stage orbiting plate having a spiral involute, a second stage inlet in fluid communication with said first stage outlet, and a second stage outlet;
• said second stage spiral involute wraps meshing with each other to define chambers, said chambers decreasing in size from said second stage inlet to said second stage outlet;
• said first stage having an expansion ratio greater than or equal to one and said second stage having a compression ratio greater than or equal to one;
• the involute spirals being provided with tip seals;
• said tip seals being extended as close as possible to the center of the involute to delay porting of gas by 180° of rotation.

A scroll pump having:

• a first stage including a first stage fixed plate having a spiral involute, a first stage orbiting plate having a spiral involute wrap, a first stage inlet, and a first stage outlet;
• said spiral involute wraps meshing with each other to define chambers, said chambers increasing in size from said first stage inlet to said first stage outlet;
• and
• a second stage including a second stage fixed plate having a spiral involute wrap, a second stage orbiting plate having a spiral involute, a second stage inlet in fluid communication with said first stage outlet, and a second stage outlet;
• said second stage spiral involute wraps meshing with each other to define chambers, said chambers decreasing in size from said first stage inlet to said first stage outlet;
• said first stage involute wraps having a central portion and an peripheral portion;
• the central portion and peripheral portions having different heights;
• the central portion of the fixed and orbiting involutes wraps being taller than the peripheral portion of the fixed and orbiting involutes.