The Different Types of Solenoid Valves and How They Work

Solenoid valves, widely used in various industrial settings, serve as automatic flow control devices. Their popularity stems from a combination of factors: a compact design, resilient fluid handling, low power consumption, and rapid responsiveness. The distinctive performance of these valves is rooted in their specific designs and the electromagnetic functions of their components.

Solenoid valves consist of a valve body housing orifices and a solenoid. This solenoid includes an inductive coil surrounding a ferromagnetic core, often referred to as a plunger. When an electric signal passes through the coil, it generates a magnetic field. This field attracts the plunger, prompting linear motion and moving the plunger within the valve body. This movement either seals or opens various valve orifices, regulating fluid flow. The magnetic force from the energized solenoid is powerful enough to overcome both inertia and opposing spring force, allowing the plunger to reach a secondary position relative to the orifice locations.

These valves are highly adaptable, boasting diverse circuit designs that enable them to control fluid flow by opening or closing, adjusting flow rates, and managing the distribution or blending of fluids in piping systems. They find application in a wide range of industries, including automated process controls, on/off fluid services, hydraulic and pneumatic loops, water and fuel supply, air conditioning systems, and wastewater treatment.

VARIOUS TYPES OF SOLENOID VALVES

Solenoid valves come in various types categorized by their actuation mode and the number of flow paths they possess. These distinguishing characteristics dictate the appropriateness of a specific solenoid valve for a particular industrial application. Engineers and system designers consider additional factors such as valve response time, coil protection, solenoid material, as well as valve and seal materials when assessing or choosing solenoid valves for different piping systems. Below is an overview of the different types of solenoid valves:

DIRECT-ACTING SOLENOID VALVES

These valves rely solely on the electromagnetic field for their operation and do not need external pressure or an additional actuator to function. Direct-acting solenoid valves can open or close even in the absence of a pressure difference across the valves. The movement of the plunger is triggered by the electromagnetic field generated when the solenoid is energized.

One common type is the 2-way valve, available in either the normally open or normally closed configuration. In the normally open setup, a spring maintains the seal away from the orifice seat, ensuring an open flow path when the coils are not energized. Applying electrical power causes an electromagnetic force, pushing the seal towards the seat and stopping the flow in the desired direction. The reverse is true for a normally closed circuit. Energizing the solenoid coil lifts the seal from the orifice seat, allowing fluid flow by opening the flow path.

Direct-acting valves feature a compact design as their actuation mechanism is housed within the valve body. The flow rates and pressure limits for fluids passing through these valves depend on the orifice sizes and the magnetic force supplied by the solenoid. They are suitable for applications requiring relatively low flow rates.

There's a unique variant of direct-acting solenoid valves available in the normally open or normally closed configuration known as "bistable" or "latching solenoids".

PILOT-OPERATED SOLENOID VALVES

These valves rely on the assistance of the service fluid's pressure for their operation. They are commonly found in fluid applications operating within a high-pressure range and with substantial flow rates. Solenoids in these valves generate ample force to control the opening and closing of pilot orifices. When the pilot orifice allows fluid in or out, it affects the top cavity, maintaining the valve diaphragms in their proper positions.

In pilot-operated solenoids, the service media moves through the solenoid's pilot orifice, exerting pressure on the upper side of the diaphragm, keeping it closed. Mechanical springs within the valves press the diaphragms against the main valve orifice, blocking flow paths to prevent fluid passage. Energizing the solenoid expels the service fluids from the top cavity, releasing them into the main pressure line. This creates a pressure difference across the diaphragm's lower and upper sides. The resultant differential pressure surpasses the force of the diaphragm and springs, opening the main valve.

Typically, the pilot valve's orifice is smaller than that of the main valve, allowing small-sized pilot valves to control large valves using minimal energy. However, these valves operate at a slower pace compared to their direct-acting counterparts. They are suitable for high-pressure hydraulic systems, steam facilities, and industrial processes demanding high flow rates.

THREE-WAY SOLENOID VALVES

These solenoid valves go beyond simple on/off fluid control in piping systems, offering additional flow control capabilities. They are suitable for mixing fluids from two different sources or diverting fluids between a common inlet and two destinations. Configurations of these valves can feature one inlet port and two outlets or two inlet ports with a common outlet, providing reliable service for fluid mixing or diversion based on their setup.

In diverting fluid flow, a 3-way solenoid valve typically has a single inlet port and two outlets. Initially, fluid flows from the inlet orifice out through one outlet while the other remains closed. When the solenoid coils are energized, the flow redirects from the initially open orifice to the initially closed outlet. For mixing applications, one inlet is open while the other is closed initially. The open inlet guides fluid through the valve, sending it out through the common outlet. Upon energizing the solenoid coil, the plunger shifts to block the initially open orifice while opening the secondary orifice to allow fluid flow.

CONCLUSION

Solenoid valves offer an affordable means to remotely activate valves, enhancing the reliability of various flow applications. Their adaptable size and design make them suitable for different fluid flow operations. When choosing these valves, it's crucial to ensure they align with the pipeline's flow conditions, the materials used in the valve body, and that the seals are compatible with the service media. This consideration ensures optimal performance and reliability in diverse operational settings.