Your Complete Guide to Everything About Solenoid Control Valve

A solenoid control valve is an electromechanical valve for use with liquid or gas. The valve is controlled by an electrical current through a solenoid coil. Solenoid control valves may have two or more ports: in the case of a two-port valve, the flow is turned on or off; in the case of a three-port valve, the outflow is switched between the two outlet ports. Multiple solenoid valves can be placed together on a manifold.

A solenoid control valve opens fully when the solenoid control is energized and closes tightly when the power is removed from it. The solenoid control valve introduces control water into the diaphragm chamber of the main valve for closing and discharges control water from the diaphragm chamber to the open valve. The control fluid is usually water from the pipeline; however, a separate source of higher pressure may be used if desired.

Solenoid Control Valves for Water

Solenoid valves for water are among the most widely used control elements in the fluid industry. Their function is to stop, release, dose, dispense or mix fluids. They are found in many application areas. Solenoid valves provide fast and safe switching, high reliability, long service life, good compatibility with materials used, low control force and compact design.

Video explaining how a solenoid control valve works

Types of solenoid valves

Normal Closed Solenoid Valve

For a normally closed (NC) solenoid valve, the valve closes when power is removed from it, preventing the flow of media through it. When current is sent to the coil, it creates an electromagnetic field that forces the piston to rise, overcoming the spring force. This causes the seal to break and the orifice to open, allowing media to flow through the valve.

A normally closed solenoid valve is ideal for applications that require the valve to be closed for extended periods of time because this is more energy efficient. It can also be used for safety reasons, if the application requires the valve to be closed without power for safety reasons (e.g. gas appliances).

Operating Principle of a Normally Closed Solenoid Valve: Inactive (left) and Energized (right).

Normally Open Solenoid Valve

For a normally open (NO) solenoid valve, the valve is open when power is removed from it, allowing media to flow through it. When current is sent to the coil, it creates an electromagnetic field that forces the piston down to overcome the spring force. A seal sits in the opening and closes it, preventing media from flowing through the valve.

A normally open solenoid valve is ideal for applications that require the valve to be open for extended periods of time as this is more energy efficient. It can also be used for safety reasons, if the application requires the valve to be open.

Biostable Solenoid Valve

A biostable or lockable solenoid valve can be switched by a momentary power supply. When power is removed, the valve remains in the switched position. Therefore, it is neither normally open nor normally closed as it remains in the current position when no power is applied. This is achieved by using a permanent magnet, rather than a spring. This gives the benefit of reduced power consumption.

Materials used in the manufacture of solenoid control valves

All materials used in the manufacture of valves are carefully selected according to the different types of applications. The body material, seal material and solenoid material are selected to optimize functional reliability, fluid compatibility, service life and cost.

Body Materials

The bodies of neutral fluid valves are made of brass and bronze. For high-temperature fluids, such as steam, corrosion-resistant steel is available. In addition, polyamide is used for economic reasons in various plastic valves.

Solenoid Materials

All parts of the solenoid actuator that come into contact with the fluid are made of austenitic corrosion-resistant steel. In this way, resistance to corrosive attack from neutral or slightly aggressive media is ensured.

Seal Materials

The specific mechanical, thermal and chemical conditions of the application affect the choice of seal material. The standard material for neutral fluids at temperatures up to 194 °F is usually FKM. For higher temperatures, EPDM and PTFE are used. PTFE is universally resistant to nearly all technically significant fluids.

Flow Rate Values

The flow rate through a valve is determined by the nature of the design and the type of flow. The valve size required for a particular application is generally determined by the Cv rating. This number is then developed for standard units and conditions, i.e., flow rate in gallons per minute and water use at a temperature between 40°F and 86°F at a pressure drop of 1 psi. Cv ratings are given for each valve. A standardized system of flow rate values is also used for pneumatic systems. In this case, the standard square foot air flow upstream and pressure drop is 15 psi at a temperature of 68°F.

Special Solenoid Valve Characteristics

Electrical Power Reduction:

The rated voltage is supplied to the valve for a short period of time to actuate the valve, then reduced to a holding voltage strong enough to hold the valve in that position while minimizing power consumption.

Latch:

The lock or pulse coil version provides a solution for low-frequency switching applications. The valve is activated by a short electrical pulse to move the piston. A permanent magnet is then used to hold the piston in this position without an additional spring or magnetic field. This reduces energy consumption and heat development in the valve.

High pressure:

The high pressure versions are designed for pressure requirements up to 250 bar.

Manual override:

The optional manual override feature provides improved safety and comfort during operation, testing, maintenance and in the event of a power failure. In some versions, the valve cannot be operated electrically when the manual control is locked.

Media separation:

The media separation design allows the media to be isolated from the working parts of the valve, making it a good solution for aggressive or slightly contaminated media.

Vacuum:

Valves that do not require a minimum differential pressure valves are suitable for rough vacuums. Direct or semi-direct acting universal solenoid valves are suitable for these applications. For more stringent leakage rate requirements, special vacuum versions are available.

Adjustable response time:

The time it takes for the valve to open or close can be adjusted, usually by turning the screws on the valve body. This feature can help prevent water hammer.

Positional Feedback:

The switching status of the solenoid valve can be indicated by electrical or optical positional feedback as a binary signal or NAMUR signal. NAMUR is a sensor output that indicates the on or off status of the valve.

Low Noise:

The valves have a dampening design to reduce noise during valve closing.

Choosing Criteria

It is essential to understand your application before selecting a solenoid valve. Here are some important selection criteria:

Sheath Material:

Select the valve sheath material based on the chemical properties and temperature of the media, but also the environment in which the valve will be located. Common choices are brass, stainless steel, PVC, aluminum, and cast iron. See Selecting the Right Sheath Material for Your Solenoid Valve for more information.

Connection Size:

Make sure the solenoid valve port sizes are the same as those to which the valve will connect.

Connector:

A solenoid connector is a device that connects to the solenoid valve to supply electricity, and helps protect the connections from dirt and water.

Voltage:

Determine the voltage of the power supply and select a solenoid valve with the corresponding solenoid.

Seal Material:

The seal material should be selected based on the chemical properties and temperature of the media. NBR, EPDM, FKM (Viton), and PTFE (Teflon) are common choices. See Selecting the Proper Seal Material for Your Solenoid Valve for a quick reference on the chemical resistance of seal materials.

Deactivation Condition:

Determine whether the application requires a normally open, normally closed, or bistable valve.

Circuit Function:

Determine whether the application requires a two-way or three-way solenoid valve.

Pressure:

The valve must be able to withstand the maximum pressure required for the application. It is equally important to note the minimum pressure as high pressure differentials can cause valve failure.

Temperature:

Ensure that the valve material can withstand the minimum and maximum temperature requirements for the application. Temperature consideration is also essential for determining valve capacity as it affects viscosity and fluid flow.

Response Time:

The response time of a valve is the time required to go from open to closed or vice versa. Small direct-acting solenoid valves react much faster than semi-direct or indirect valves.

Approvals:

Ensure that the valve is properly approved for the application.

Degree of Protection:

Make sure the valve has the appropriate IP rating for protection against dust, liquids, moisture and contact.