A injection pump includes a needle valve which is disposed in the pump body cap. An air actuator valve is disposed in the pump piston head. The amount of air fed is controlled by the gap between the needle valve and a needle valve seat which is also located in the pump body cap. At the end of the pumping stroke, a spring on the air actuator valve contacts the bottom surface of the body cylinder chamber to cause the air actuator valve to open and release the trapped air from the body cylinder chamber through the air actuator valve so that the air can exit the pump. This action allows the spring around the piston and plunger to release and return the piston and plunger to the starting position.