US Patent 8459509 Fluid dispensing apparatus

A fluid dispensing apparatus includes a fluid reservoir and a dispensing assembly. The dispensing assembly includes a housing and a deformable member that define a metering chamber that is configured to receive a predetermined volume of fluid from the fluid reservoir. The deformable member is deformed from a rest position to an eject position and the deformation causes the volume of the metering chamber to change which results in a change in fluid pressure within the metering chamber. An increase in the fluid pressure within metering chamber causes a predetermined volume of fluid within the metering chamber to be ejected and a decrease in the fluid pressure within the metering chamber causes fluid to be drawn into the metering chamber from the reservoir.