Piston operated pumps for liquid carbon dioxide

Claim 1

A PISTON PUMP APPARATUS ADAPTED TO PUMP LIQUID CARBON DIOXIDE, COMPRISING A CYLINDER MEMBER HAVING A PUMPING CHAMBER THEREIN, A PISTON MEMBER RECIPROCALLY SLIDABLE WITHIN THE CYLINDER MEMBER TO PUMP FLUID FROM THE PUMPING CHAMBER, THE MEMBERS BEING SIZES SUCH THAT LIQUID CARBON DIOXIDE LEAKS FROM THE CHAMBER BETWEEN THE MEMBERS, AT LEAST ONE OF SAID MEMBERS HAVING A CAVITY THEREIN OPENING LATERALLY AGAINST THE OTHER MEMBER, A SOURCE OF GAS UNDER A PRESSURE GREATER THAN THE TRIPLE POINT PRESSURE OF THE CARBON DIOXIDE BEING PUMPED, AND CONDUIT MEANS COUPLING SAID SOURCE OF GAS AND SAID CAVITY FOR APPLYING THE GAS UNDER SAID GREATER PRESSURE TO THE SPACE BETWEEN THE PISTON MEMBER AND THE CYLINDER MEMBER WALL, WHEREBY WHEN SAID GAS IS SUPPLIED TO THE CAVITY AND APPLIED TO THE LIQUID CARBON DIOXIDE WHICH LEAKS FROM THE PUMPING CHAMBER BETWEEN THE PISTON MEMBER AND THE CYLINDER MEMBER WALL, IT WILL PREVENT LIQUID CARBON DIOXIDE FROM SOLIDIFYING BETWEEN THE PISTON MEMBER AND CYLINDER MEMBER WALL.