Abstract: An apparatus and method for injecting a liquid product or chemical into a main water supply line used for agricultural or industrial purposes. A pressure regulating bypass valve has an inlet side connected to an outlet line of a multi-ganged, diaphragm pump. The pump is run at a constant speed and produces a non-pulsatile flow of product. The bypass line of the valve is connected to an inlet line of the pump. The bypass valve is set at a predetermined pressure, discharging any excess product into the bypass line. The product line at the outlet side of the bypass valve progresses in serial fashion to an electronic control valve, a product flow meter, and a check valve. The output side of the check valve is interconnected to the main water supply line for injection of product therein. A water flow meter is also provided in the main water supply line.