+1 The fire pump with a capacity of 500 gallons/minute is usually 50 horsepower. As for the number of "pistons" inside the engine, it depends on the type of pump engine: Diesel engine: It usually comes with 4 pistons (4 cylinders) or 6 pistons (6 cylinders) depending on the engine manufacturer and the required torque. Electric engine: It does not have a piston system, but relies on a "rotor" or rotating member that depends on electromagnetic induction.