Metering pump

A metering pump comprising a pair of positive displacement pumping chambers having different displacement volumes, liquid supply passage means having an inlet and in communication with both of said pumping chambers, inlet check valve means for permitting liquid flow into said pumping chambers during expansion thereof from said liquid supply passage means, liquid discharge passage means having an outlet and in communication with both of said pumping chambers, outlet check valve means for permitting the discharge of metered liquid from said pumping chambers upon contraction of the same into said discharge passage means, power means for expanding and contracting said respective chambers automatically through a preselected number of repetitive identical pumping cycles, and means independently controllable for each of said pumping chambers for automatically and selectively interconnecting of disconnecting said power means and a respective pumping chamber for operating each pumping chamber for a required number of cycles corresponding to said preselected number to automatically meter a precise volume of liquid into said discharge passage means.