3.5.Valve:
The control valve is an “automatic metering solenoid” valve. While most solenoids operate in either the fully open or fully closed state, the automatic metering solenoid valve is designed to control flow (see Figure 3.6). A spring, connected to the plunger assembly, holds a magnetic plunger tightly against an orifice to shut off flow. The magnetic plunger is surrounded by an electrical coil, which when energized with electrical current lifts the plunger off the orifice and allows flow to pass between the orifice and the plunger seat. Controlling the current through the coil controls the distance between the orifice and the plunger seat, thus effectively controlling the flow through the valve. This current is controlled by a feedback loop that matches the transducer output with the command voltage.
Figure 3.6
