A pressurized gas cartridge drives a dispensing device for viscous product cartridges. The dispensing device and the viscous product cartridge form a gas enclosure separated from a product enclosure by a movable wall. A valve is driven by a rack and pinion valve drive mechanism between an open position and a closed position upon rotation of the pinion. The rack rotates the pinion upon linear movement thereof. A trigger is adapted to impart linear movement to the rack upon manual actuation of the trigger. The open position of the nozzle valve permits viscous product to flow through the dispensing passage, and the closed position of the nozzle valve prevents viscous product from flowing through the dispensing passage. The interface between the trigger and rack is designed to operationally disengage rather than transmit a force therebetween that is capable of damaging the device.