For many years, it has been known to dispense liquids, such as soaps, sanitizers, cleansers, disinfectants, and the like from a dispenser housing maintaining a refill unit that holds the liquid and provides the pump mechanisms for dispensing the liquid. The pump mechanism employed with such dispensers has typically been a liquid pump, simply dispensing a predetermined quantity of the liquid upon movement of an actuator. Recently, for purposes of effectiveness and economy, it has become desirable to dispense the liquids in the form of foam generated by the interjection of air into the liquid. Accordingly, the standard liquid pump has given way to a foam generating pump, which necessarily requires means for combining the air and liquid in such a manner as to generate the desired foam.
Typically foam dispensers generate foam by pumping a foamable liquid stream and an air stream to a mixing area and forcing the mixture through a screen to better disperse the air as bubbles within the foamable liquid and create a more uniform foam product. The more minute and numerous the air bubbles the thicker and softer the foam, although too much or too little air can cause the foam to be of poor quality. The key to a desirable foam product is violent mixing of the foamable liquid and air to disperse the air bubbles within the liquid. Many existing foam pump designs employ a piston type mechanism, which results in a fixed volume of foam generated by each activation of the foam pump, without any ability to adjust. Thus, there is a need for a foam pump providing the ability to adjust the volume of foam provided by each activation of the foam pump.