Understanding Solenoid Valve Operation and Their Types

Valves are indispensable components of fluid systems, allowing for the regulation and control of fluid flow and pressure. Solenoid valves in particular are a type of electrically controlled valve, allowing for remote control for opening and closing. Solenoid valves are extremely useful, allowing for more complex piping systems that can utilize automatic control to both create an ease of operation, as well as increase safety of workers for plumbing systems that are in hazardous areas.

A typical solenoid valve consists of two parts, those being the valve body and the solenoid. The solenoid is a type of electromagnet, and an inductive coil is wrapped around an iron core at the plunger. When not induced with electricity, the solenoid valve will remain in a de-energized state in which it will remain open or closed based on its default configuration. When an electrical current is passed through the solenoid, the coil begins to produce a magnetic field. With the magnetic field, the valve plunger begins to be attracted, and it overcomes the force of the spring that maintains its default positioning. If the valve is a closed solenoid valve, the valve plunger is lifted to open up the seal of the orifice. On the other hand, energizing the solenoid may also be used to close open solenoid valves by forcing the plunger down through magnetism.

Due to their ability, solenoid valves are utilized in a diverse set of applications ranging from low to high pressure systems, as well as small and large flow rate systems. Depending on the need, different powered valves may be implemented, each providing the ability to open, close, dose, distribute, or mix fluids within a piping system. Across different powered valve components, the two most common solenoid valve types are 2-way and 3-way valves. The 2-way solenoid valve contains two ports which serve as the inlet and outlet. To ensure that the valve is installed correctly, most will display a visual that indicates the direction of flow. 3-way solenoid valves feature a third connection port, generally allowing for two states or positions for operation. By energizing a 3-way valve, fluids can be switched between two separate circuits to either open, close, distribute, or mix fluids.

Beyond the physical configuration of solenoid valves, there are also various working principle types. Direct acting solenoid valves are the most simple, and they often come in the form of 2-way valves that allow for opening and closing of orifices by energizing the solenoid. The maximum amount of flow and pressure through the valve is dictated by the diameter of the valve orifice as well as the amount of magnetic force generated by the solenoid. Because of this, most direct acting solenoid valves are reserved for applications in which there is a small flow rate.

Indirect acting solenoid valves, often referred to as servo or pilot operated, are those that use a pressure differential of the medium in order to open and close the valve orifice. Within such valves, a rubber membrane acts as a diaphragm, and a small hole within the membrane allows for the medium to enter the upper compartment of the valve. When the solenoid of the valve is energized, the orifice of the pilot is opened, and the pressure above the membrane begins to decrease. Once a pressure difference on each side of the membrane increases to a certain limit, the membrane lifts and the flow of fluids is permitted.

Semi-direct acting solenoid valves utilize principles of both indirect and direct acting valves, permitting a high flow rate and operation from zero bar. While the valve features a membrane as well, the solenoid plunger is directly attached to the membrane, allowing for it to be lifted when the solenoid is energized. As the membrane is lifted, a second orifice is also opened by a plunger, providing a larger orifice to increase pressure for optimal flow.

The last major type of valve is the 3-way direct acting solenoid valve, and they feature three ports for mixing and diverting fluids. Within such solenoid valves, one port is open and one is closed by a plunger, forcing fluids to flow only in the desired direction. Once energized, the plunger forces the change of blockage, allowing for a diversion of fluid direction. Depending on the configuration and need, a 3-way direct acting solenoid valve may be for diverting, mixing, or universal direction.


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