Sold Out- The pump operates only when there is an adequate supply of syrup. Vacuum produced by the pump evacuates the syrup within the bag. Once the preset vacuum point is achieved and held, the gas supply to the pump is shut off, causing the pump to stop. When a new BIB is installed, the pump automatically starts and pressurizes the system. The benefit of the sold-out feature is that the outlet line to the dispenser always remains full of syrup.