Reciprocating type liquid pump driven by cam

A reciprocating type liquid pump driven by a cam comprises a shell, four cavities with fixed volumes are distributed in the shell at intervals, the four cavities comprise two liquid inlet cavities and two liquid outlet cavities, the liquid inlet cavities and the liquid outlet cavities are distributed alternately, liquid inlets are formed in the outer circle faces of the liquid inlet cavities, and liquid outlets are formed in the outer circle faces of the liquid outlet cavities; a volume-variable piston cylinder is arranged between the liquid inlet cavity and the liquid outlet cavity, a one-way valve allowing liquid to enter the piston cylinder from the liquid inlet cavity is arranged between the liquid inlet cavity and the piston cylinder, and a one-way valve allowing liquid to enter the liquid outlet cavity from the piston cylinder is arranged between the liquid outlet cavity and the piston cylinder. A driving mechanism capable of achieving volume change of the piston cylinders is arranged in the shell and c