Directional valves affect the start/stop and flow direction of the hydraulic fluid, and thereby control the movement of the actuators in a hydraulic system. Their function is to direct the flow of hydraulic medium in certain directions therefore connecting or disconnecting the relevant connections.
Distinctions are made:
Working method: Switching directional valves (with positive or negative overlap- and continuously adjustable directional valves (with a positive, negative or zero cut overlap).
Construction design: piston or and seated valves.
Task: Valves with 2, 3, 4, sometimes 5 and more lines (ports) and with 2, 3, sometimes 4 switching positions.
The directional valves are identified based on the number of usable connections and switching positions. Thus in hydraulics:
2/2-way directional valves: Valves with two controlled ports and two switching positions (open and closed);
3/2-way directional valves: Valves with three controlled ports and two switching positions (open and closed);single action consumers;
3/3-way directional valves: As above, but with a centre position with different design forms
4/2-way directional valves: Valves with four controlled ports and two switching positions to control a dual action consumer;
4/3-way directional valves: As above, but with a centre position with several design forms;
5/3-way directional valves: As above, but with two separate tank connections. The valve does not match the ISOhole pattern and is therefore rarely still used despite certain advantages.
In addition, there are also special designs with even more ports and/or switching positions (e.g. 4/4 or 6/4 directional valves).