What is a solenoid valve?

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Solenoid valves are vital components wherever the flow of a fluid needs to be controlled automatically. The basic design may have evolved since Bürkert introduced the first plastic-moulded body solenoid valves in the 1950s, but the general principles remain the same. Only now there is a solenoid valve for every application. Kelly Booth, solenoid valve specialist at Bürkert UK, explains how to select the right solenoid valve for your application.

 

You would think that selecting a solenoid valve was a straightforward process. However, in actual fact, it’s a decision that calls for in-depth knowledge of the process under control. Not to mention a good understanding of the materials and designs available. Matching the most applicable solenoid valve design to your application will ultimately save you a great deal of time, money and headaches in the long run.

 

What is a solenoid valve?

 

A solenoid valve is an electro-mechanical valve used to control the flow of liquid or gas. Solenoid valves convert an electrical signal into a mechanical movement. The signal is sent to a coil and the movement occurs inside the valve. Solenoid valves can be categorised into two main types: pilot operated or direct acting.

 

Pilot operated solenoid valves

 

Two-way pilot operated solenoid valves have two chambers separated by a diaphragm. “In this design, there is a pilot and bleed orifice that uses line pressure to operate the main valve,” says Kelly Booth, solenoid valve specialist at Bürkert UK. “When the solenoid is energised, the coil opens the pilot orifice and relieves pressure from the top of the valve piston or diaphragm to the outlet side of the valve. 

 

“This results in an unbalanced pressure, lifting the piston or diaphragm off the main orifice. When the solenoid is de-energised, the pilot orifice is closed and full line pressure is applied to the top of the piston or diaphragm, which together with spring assistance, closes the valve.

 

“Pilot operated solenoid valves require a minimum pressure differential across the valve to keep them open or closed and therefore they can only operate with a suitable upstream pressure differential and do not operate at zero pressure. Pilot operated solenoid valves can provide high flow rates at high pressures, with lower power consumption,” adds Kelly.

 

Direct acting solenoid valves

 

Direct acting solenoid valves don’t use a diaphragm, their seal is part of the moving core. “The first and most obvious characteristic of a solenoid valve is to determine whether it is direct acting or pilot operated,” says Kelly. “With a direct acting solenoid valve, the action of the solenoid plunger directly opens or closes the orifice. This type of solenoid is required when there is no line pressure to maintain the valve in the desired position.

 

“A normally closed (NC) version will use a spring to keep the valve closed until the solenoid is energised and the coil will lift the plunger against the spring force to open the valve. Conversely, a normally open (NO) design uses the spring to keep the valve open, allowing the media to flow until the solenoid is energised,” she adds.

 

Pivots, rockers and flippers

 

The armature design of the valve should be carefully considered in relation to the media being controlled. “Pivoted armatures allow the use of a media separating diaphragm, which enables the valve to be used in applications involving corrosive, contaminated or aggressive fluids,” says Kelly. “This style of valve can be mounted in a manifold and, unlike the plunger type, the 3/2-way version has all three ports in the same plane.

 

“An alternative design is the rocker armature which is often used in microfluidic applications where small dead volumes and flush-ability are of prime importance. The compact design, combined with the small and efficient coil, enhance the suitability for aggressive or ultra-pure media. These attributes also make the design suitable as a pilot for pneumatic control valves in both hazardous and non-hazardous areas.”

 

A further alternative is the flipper design. “The flipper design uses a vertical armature that moves a flexible sealing system between two opposing seats. Bürkert has developed this principle for microfluidics with the possibility of using a valve that is only 4.5 mm wide. Again the compact design and encapsulated sealing make this type of solenoid valve suitable for applications involving both aggressive and ultra-pure media.”

 

The solenoid valve reigns supreme in fluid control systems. Although, care must be taken to specify the right solenoid for the job  to achieve reliable and efficient service. Regardless of whether you’re designing a new system, or replacing an existing component, Bürkert has the expertise and experience to guide your selection process. Whether your application is filling, level, flow, pressure or temperature, we have the ideal solution.

 

For more information, please visit Bürkert.

Bürkert is a world-leading manufacturer of control and measuring systems for fluids and gases. With a wide range of solenoid valves and other control instrumentation, they have the facility to adapt and develop existing technology to suit customer needs. Their products are suitable for a wide range of applications, including renewables, food and beverage, pharmaceuticals, water treatment, gas handling and microfluidics. For more information, contact the Bürkert sales team on +44 (0)1285 648 720.

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