A 4-way solenoid valve is a device that controls flow of gases or liquids in multiple directions. Sometimes referred to as a "5-port valve," this device can be powered by air or electricity, with air pressure control being the most common. The reason there are five ports, or connection points, is to permit air pressure to move an actuator or rod back and forth inside the valve to control where a fluid goes.
One common design of a 4-way solenoid is one liquid inlet and two outlets, with the flow direction controlled by the position of the internal actuator. The other two ports, one on each end, are for the air pressure connections. As air pressure is introduced at one end, the rod moves and internal channels permit the fluid to flow in one direction. If air pressure is introduced at the other end, the rod moves in the opposite direction, exposing a different flow channel that permits fluid to go in another direction.
These valves are useful because they allow one device to control flow in different directions. They also can be an advantage when a control system has only a minimum of connections available, so one valve can be used for more than one control task. A 4-way solenoid is a simple device with minimum parts, and manufacturers test them for thousands of operating cycles to confirm their dependability.
Another type of 4-way solenoid is a stepper valve that uses a ratchet system to advance the valve each time it is activated. Gears inside the valve move the actuator to a different position each time air pressure or an electrical signal is sent. This valve can be used to turn flow off and on in a set order, or to activate different systems connected to the valve.
Stepper valves have some limitations. As long as the valve is operating, each signal turns the valve to a new position, without the ability to return to a previous position. When a signal is lost or the valve cycle is complete, it will return to its original position, allowing the cycle to begin again. These valves are best suited for operations that occur in order, called sequential positioning, without the need to go back or jump to a different position. Typical uses are lawn sprinklers, water softener regeneration, and pool chemical treatment.
With the development of computer-controlled systems in the late 20th century, 4-way solenoid valves became "intelligent" systems, which could use sensor readings. As signals were sent from various points in a chemical process, as an example, the solenoid could make decisions on how to operate. These valves contained software programming that allowed them to make operating choices, without requiring a connection to a central control circuit.