Solenoid valves

Solenoid valve

A solenoid valve is an electromechanical device in which the solenoid valve uses an electric current to generate a magnetic field and thus activates a mechanism that controls the opening of the liquid flow in a valve.

Solenoid valves differ in the characteristics of the electric current they use, the strength of the magnetic field they generate, the mechanism they use to regulate the fluid, and the type and characteristics of the fluid they control. The mechanism of the solenoid valve varies from linear operation, plunger-powered actuators to rotary armature actuators and rocker actuators. The solenoid valve can use a two-port design to control a flow or use a three- or multi-port design to switch the flows between the ports. Multiple solenoid valves can be placed together on a manifold.

The solenoid valve is the most widely used control element in the fluid industry.

Tasks of a solenoid valve include

• shutting down the mixing of fluids.
• releasing mixing fluids.
• dosing mixing of liquids.
• distributing mixing liquids.

Advantages of solenoid valves

They can be found in many areas of application. Solenoid valves (also called solenoids) offer fast and safe switching, high reliability, long life, good average compatibility of the materials used, low regulating power and compact design.

Operation of solenoid valve

There are many variations in valve design. Solenoid valves can have many ports and fluid paths. For example, a 2-way solenoid valve has 2 ports; when the valve is open, the two ports are connected and fluid can flow between them; when the valve is closed, the ports are insulated. If the valve is open when the solenoid valve is not live, then the valve is normally called open (N.O.). Similarly, if the valve is closed when the solenoid is not activated, then the valve is normally called closed (NC). There are also 3-way and more complicated designs. A 3-way valve has 3 ports; it connects one of the two other ports (usually an inlet port and an outlet port).

Solenoid valves are also characterised by the way they work. A magnet of a solenoid valve can generate a limited force. If this force is sufficient to open and close the valve, it is a direct-acting solenoid valve.

At higher pressures or smaller magnets, high forces are required for operation. To generate these forces, an internally controlled solenoid valve construction can be used which uses the line pressure to generate the high valve forces; a pilot valve (servo) controls how the line pressure is used. servo-controlled valves are used in dishwashers and irrigation systems where the liquid is water and there is always a pre-pressure present.

Actuation

In some solenoid valves, the magnet acts directly on the main valve. Others use a small, complete solenoid valve, known as a pilot, to operate a larger valve. The second type is actually a solenoid valve combined with a pneumatically operated valve, but they are sold and packaged as a single unit, called a solenoid valve. Servo-operated valves require far less power to regulate, but they are noticeably slower. Servo-assisted solenoid valves usually require full power at all times to open and stay open, with a direct-acting solenoid valve requiring only full power for a short period of time to open it, and only low power to hold it.

A direct-acting solenoid valve usually works in 5 to 10 milliseconds. The operating time of a controlled valve depends on its size; typical values are 15 to 150 milliseconds.

The power consumption of the solenoid valves varies per application and is mainly determined by the fluid pressure and the pipe diameter. For example, a popular 3/4" 10 bar sprinkler valve, designed for 24 VAC (50 Hz), has a short-term duty cycle of 7.2 VA, and a required holding capacity of 4.6 VA. An industrial 1/2" 700 bar solenoid valve, designed for 12, 24, or 230 VAC systems in high-pressure liquid and cryogenic systems, has a duty cycle of 300 VA and a holding current of 22 VA.

Although there are several design variants, the following is a detailed breakdown of a typical solenoid valve design.

Solenoid valve parts

A solenoid valve consists of two main parts: the solenoid valve and the valve. The solenoid converts electrical energy into mechanical energy, which in turn opens or closes the valve mechanically. A direct-acting valve has only a small circuit. In this example, a diaphragm control valve multiplies this small control current by using it to control the current through a much larger opening.

Solenoid valves can use metal seals or rubber seals, and can also be equipped with electrical interfaces for easy control. A spring can be used to keep the valve open (normally open) or closed (normally closed) while the valve is not activated.