Cryogenic pump for liquid gases

A cryogenic pump for liquid gases, comprising a housing, a cylinder within the housing, a piston reciprocable in the cylinder and dividing the cylinder into a suction chamber and an evacuation chamber on opposite sides of the piston, a one-way valve for admitting liquefied gas into said suction chamber, an overflow duct for exhausting fluid from said evacuation chamber, said overflow duct being permanently and directly connected to said evacuation chamber, said suction chamber being permanently connected to an inlet duct through said one-way valve, a piston rigidly fixed to the housing and extending into said evacuation chamber, a high pressure outlet of said pump extending through said piston, a one-way valve permitting flow of liquefied gas through said outlet only in an outlet direction, a skirt carried by said movable piston and cooperating with said fixed piston to define a compression chamber, a one-way valve permitting flow of liquefied gas through said piston from said suction chamber into said compression chamber, another one-way valve that connects the suction chamber to the overflow duct for evacuation from the suction chamber of that fluid which is in excess of the liquefied gas necessary to fill said compression chamber, and means directly interconnecting said suction chamber with said outlet duct when said piston is adjacent the end of its movement into he evacuation chamber, thereby to exhaust from said suction chamber any said gas which is in vapor phase.