Page 476 - Mechatronics with Experiments

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FIGURE 7.44: Valve categories: (a) number of ports (also called ways): two port (or two-way),
three port, four port valves, (b) two, three, and four port valves with two, three, and four
position configurations, (c) same valves with proportional flow metering capability
(proportional valves), (d) normally closed, normally open conditions, that is the flow condition
of the valve, when it is in default condition, (e) three port valve with various discrete positions,
(f) various flow conditions when a four port valve is in the center position (closed center,
tandem center, open center, float center), (g) actuation method of the valve: manual, pilot,
solenoid or the combinations of them.

Most proportional valve geometries are designed so that the flow is approximately propor-
tional to the spool displacement under a constant pressure drop across the valve.
Valves can be categorized according to the following:

1. number of ports, that is two, three, four ports,
2. number of discrete positions of the spool, that is one, two, or three discrete positions
or ability to position the spool proportionally within its travel range,
3. flow condition of the valve at the center position, that is open center, closed center,
4. actuation method of valve, that is manual, electric actuator, pilot actuated, or a
combination of them.
5. metering element type: sliding spool, rotary spool, poppet (or ball),