Two-stage volumetric pump for liquefied petroleum gases in liquid phase

A positive displacement pump having at least two stages for pumping liquefied petroleum gases in substantially a liquid form, said pump comprising:

• a housing;
• at least two separate chambers formed in said housing, each chamber have one wall that is formed by a diaphragm, said diaphragm being freely deformable in a direction to increase the volume of each chamber and deformable in the opposite direction under the action of actuating means;
• a passageway connecting said chambers, said passageway having a non-return valve positioned therein for allowing flow from a first one of said chambers to the other of said chambers while preventing flow from the other chamber to the first chamber;
• an inlet means for said first one of said chambers, said inlet means having a non-return valve positioned therein to allow fluid to flow into said first one of said chambers;
• an outlet means for said other of said chambers, said outlet means having a non-return valve positioned therein to allow fluid to flow out of said other chamber of said chambers;
• a double ended piston disposed in said housing, each end of said piston contacting one of said diaphragms, said piston being sealed in said housing to isolate said chambers from the outside;
• a driving means coupled to said piston to reciprocate said piston;
• and
• a passageway disposed to connect the spaces on the side of said diaphragm opposite said pump chambers to equalize the pressures in said spaces.