US Patent 6892899 Passive syrup delivery system

A pump transfers syrup through a supply line and through a valve assembly for mixing with ice cream in a mixing chamber to form a frozen dessert or milkshake. When the syrup flows through the passive valve, the pressure along the supply line increases. When syrup delivery is complete, a first timer is initiated to dispense ice cream into the mixing chamber for 0.4 seconds to flush out any remaining syrup. A second timer is also initiated when the syrup delivery is complete to reverse the pump for 0.2 seconds to remove the residual pressure in the supply line. By removing the residuals pressure, syrup in the supply line is prevented from oozing out of the valve apparatus and into the mixing chamber.