spool pneumatic directional control valve / pneumatically-operated / electrically-operated / 5/2-way

Starting from a series of sturdy, reliable valves, such as those to ISO
5599/1, some special features have been added, such as the presence
of a valve status diagnostic system and the creation of a double channel
guaranteeing architecture redundancy.
The simplest version features one electropneumatically-operated 5/2
monostable valve. It is common knowledge that when this type of valve
is in the idle state (coil not energized), port 1 is connected to port 2, and
port 4 relieves. When the valve is operated (coil energized), port 1 is
connected to port 4, and port 2 relieves. When the coil is de-energized
again, the valve is returned to the idle state (so port 4 relieves) by means
of a spring that returns the spool to the home position.
In the event of a failure, the spool may remain in the actuating position,
even with coil de-energized, leaving port 4 pressurized.
To offset this problem, we have added a Hall-effect sensor that reads the
spool position. This means that when the valve is deactivated, the sensor
is on, and when the valve is activated, the sensor is off. A status in which
the sensor is off and the coil de-energized indicates a problem.