Cryogenic pump

A pump for pumping a cryogenic liquid comprising:

• a. a pump housing defining a cylinder;
• b. a piston slidably positioned within the cylinder so that an intermediate fluid chamber that is configured to receive an intermediate fluid is defined within the cylinder adjacent to a first end of the piston and a fluid pumping chamber is defined within the cylinder adjacent to a second end of the piston, said fluid pumping chamber including an inlet and an outlet;
• c. an intermediate fluid seal attached to the piston and configured to engage the cylinder;
• d. a pumped fluid seal attached to the piston and configured to engage the cylinder, said pumped fluid seal spaced from the intermediate fluid seal so that a differential pressure space is defined within the cylinder between the intermediate fluid and pumped fluid seals;
• e. a differential pressure vent valve in fluid communication with the differential pressure space;
• f. a differential pressure switch operatively connected to the differential pressure vent valve and configured to sense a pressure within the differential pressure space and a pressure within the intermediate fluid chamber, compare the pressures sensed in the differential pressure space and the intermediate fluid chamber and to open the differential pressure vent valve when the pressure within the differential pressure space reaches a predetermined pressure level that is below a pressure of the intermediate fluid within the intermediate fluid chamber.