Solenoid valves are control units which, when electrically energized or de-energized, either shut off or allow fluid flow. Three-way valves have three port connections and two valve seats. One valve seal always remains open and the other closed in the de-energized mode. When the coil is energized, the mode reverses. The 3-way valve is designed with a plunger type core. Various valve operations can be obtained according to how the fluid medium is connected to the working ports. The fluid pressure builds up under the valve seat. With the coil de-energized, a conical spring holds the lower core seal tightly against the valve seat and shuts off the fluid flow. When the coil is energized the core is pulled in, the spring-loaded upper core seal seals off the valve seat. The fluid medium now flows through the valves.