The most common replacement parts on the Fastek Solenoid Valves are the coils.  We offer a wide range of valve coils which are usually interchangeable with other manufacturers also.  When selecting the proper coil, please note the valve series for the size along with the voltage and wattage which is usually stamped on the side of the coil.  The 100 Series coils have the voltage molded into end of the coil.  Generally 4-way valve coils will work at about 3 watts of power while small 2-way valves need at least 4.8 watts to work reliably.