Abstract: Disclosed herein is an on-demand fluid pump having a solenoid actuated reciprocating piston. The pump's electrical circuit comprises an oscillator generating at predetermined intervals short duty cycle sample signals which are applied to the solenoid. The reciprocating piston is nonresponsive to the applied sample signals, however, the sample signals induce a signal in a position sensor. The value of the signal induced in the position sensor is a function of the piston's position. A detector circuit generates a signal switching a bi-stable electronic switch to a SET state in response to an induced signal having a value indicative of the piston being at the end of its spring actuated pump stroke. The bi-stable switch in the SET state activates the solenoid to retract the piston against the force of the spring. The next sequential sample signal resets the bi-stable switch to its RESET state deactivating the solenoid.