Elements of Electric Valves for Refrigerant Control
Solenoid valves are commonly used as shutoff valves and are simple in design. When a coil surrounding a plunger is energized, the magnetic field lifts the plunger (Figure 1). The valves are designed to have the plunger. This type of valve is either open or closed and has no ability to modulate flow.
To be successful as a modulation valve, a solenoid must be opened and shut rapidly in response to a signal generated by a controller. The term pulse width modulation (PWM), or simply pulse, is used for this design. Mechanical limits of the design confine the load following ability, or resolution, to a very narrow range.