A submersible pneumatic canister pump system for pumping liquid from a tank or underground location by incorporating a valve inside the pump for preventing air from exiting with the liquid discharge. The floating-ball valve is located near the lower end of the pump and communicates with the discharge pipe. When liquid level approaches the lower end of the pump, a ball of lighter density than the liquid rests on a seat and prevents further discharge of liquid and the passage of air out of the pump. Also various pump control arrangements can be used to operate the pump and a quick-passage check valve can be used to enhance operation.