Patent ID: 7574863

Claim:
A fluid pump provided with: a fluid vessel in which a fluid is sealed in a flowable manner, a heater heating and vaporizing the fluid in the fluid vessel to produce steam, a cooler arranged below said heater, the cooler cooling and liquefying steam obtained by vaporization by the heating by said heater in said fluid vessel, a discharge side fluid passage discharging liquid in said fluid vessel to the outside, a suction side fluid passage sucking liquid into a fluid vessel from the outside, a piston provided movably in a pipe connecting said fluid vessel and said discharge side fluid passage and said suction side fluid passage, means for storing part of the expansion energy received by said piston at a time of said expansion of the steam and using the stored energy to compress the steam and liquid when said steam liquefies, a first passage formed in said piston and communicating said fluid vessel and said discharge side fluid passage when said piston moves to said fluid vessel side, and a second passage formed in said piston together with said first passage and communicating said fluid vessel and said suction side fluid passage when said piston moves to the opposite side from said fluid vessel.