Pump with back suction phase

Abstract

The present invention provides a pump for pumping fluids, especially highly viscous fluids such as shampoo, from a main fluid container through a nozzle without unwanted dripping, plugging, or mess. A piston reciprocates in a pump chamber, creating positive and negative pressure alternately in the pump chamber. Positive pressure in the pump chamber initiates a discharge phase of operation, wherein the fluid in the pump chamber is forced from the pump chamber through a discharge valve. Negative pressure in the pump chamber causes both a back-suction phase and a suction phase of operation. Back-suction occurs in the pump chamber immediately following the discharge phase, drawing any fluid remaining in an exit passage back through the discharge valve into the pump chamber. The suction phase starts immediately after the discharge valve closes at the end of the back-suction phase. During the suction phase, the negative pressure in the pump chamber draws fluid from the main fluid container through the suction valve and into the pump chamber. A resilient spring member biases the suction valve into a closed position during periods of non-use, especially when the pressure in the main fluid container increases due to an increase in temperature. The strength of the resilient spring member is established at a value which maintains the suction valve closed until a predetermined negative pressure is established across it.