The solenoid valve converts electrical energy into mechanical energy, causing a magnetic response. Through the wire coil, an electrical current activates the solenoid. During a fluid power system’s operation, solenoids control the flow of fluid in hydraulic valves and pneumatic valves. Direct-acting and pilot-operated solenoid valves are the two main types of solenoid valves available. It is important to look at the application before selecting a solenoid valve and to ensure you are choosing the correct valve.
Solenoids had been used as a triggering mechanism for quite some time, but it wasn’t until the Industrial Revolution where they became more prevalent as a real-world tool. In the past, they were very costly and difficult to produce, but as technology progressed, this has allowed them to become more affordable and widely available. The first known use for a solenoid valve was invented in 1824 by Joseph B. Taylor who devised a magnetically powered valve that was used with a combination of HVAC and a steam-powered piston engine.
Types of solenoid valves:
I) Direct-acting valves
Due to their direct mechanism, solenoids in direct-acting valves open the valve with magnetic force. During electrical operation, the coil pushes and pulls a shaft, causing the valve seat to shift. The coil of the spring returns to its default position if there is no electricity to power it. In order to operate a direct-acting valve, the entire power supply must be applied. It depends on the application whether the position is normally open or closed.
A normally closed valve with an energized solenoid coil allows fluid to pass through its outlet when the coil retracts, thus releasing the inlet pressure. As compared to pilot operated valves, direct acting valves usually have larger solenoids.
II) Pilot-operated valves
In pilot operated valves, the fluid pressure in the line opens the valve. A benefit of using a smaller coil is the lower cost and ability to utilize a smaller coil. Despite using less electricity, pilot-operated valves also require adequate pressure to operate.
Type of Valve
There are three types of solenoid valves: two-way, three-way, and four-way. You should choose solenoid valves based on the application.
I) Two-Way Valves
Two-way valves are used in On/Off applications that require quick response times and high flow. To automate an operation, two-way valves can replace levers. Valve actuators are used in venting applications to relieve excess pressure on fluids.
II) Three-Way Valves
There are three ports on a three-way valve. A circuit may be in any of two states. A three-way valve can be opened, closed, conveyed, distributed, or combined.
III) Four-Way Valves
By default, all ports of a four-way valve are in the off position. Each of them creates two states and has two exhaust ports. By attaching flow control valves to each exhaust port, you can regulate the speed of each action.
Operation: Normally Closed vs. Normally Open
If the valve is de-energized, it remains in the “Closed” position, which is the most common form of operation. In On/Off and venting applications, normally closed valves are used because when power is lost, the process should stop. During a power outage, the valve closes, and the fluid does not exhaust.
If the valve is de-energized, it remains in the “Open” position. A normally open valve’s most common application is in safety applications where there is a loss of power when the process runs out.
According to the way the valve is piped, it can either be Normally Closed or Normally Open. This is most common in 3- and 4-way valves since any port of the valve can be put under pressure. A 3-way valve, for example, would have supply ports, exhaust ports, and delivery ports. It provides flexibility in application and allows you to customize it however you see fit.
Solenoid Valve Uses
Solenoids are used in fluid power pneumatic and hydraulic systems, to control cylinders, motors, and larger industrial valves. A solenoid valve with an automatic controller is also used in automatic irrigation sprinkler systems. To control water flow into washing machines and dishwashers, solenoid valves are used. They are also commonly used in paintball guns for actuating the CO2 hammer valve. Solenoids are often referred to as solenoid valves.
There is no end to the applications of solenoid valves in the industry, including general on-off control, calibration and test stands, process control loops, and a variety of OEM applications.
How to choose an AC or DC solenoid valve coil
Essentially, DC solenoids work by allowing magnetic force generated by the solenoid to overcome spring resistance and move the armature toward the coil’s center, or by de-energizing the solenoid and allowing its spring force to return it to its starting position.
AC solenoids have a slightly more complex theory of operation. We can approximate AC current using a sinusoidal waveform. The result is that twice per period, the current has a zero-crossing, meaning the current flowing through the coil is equal to zero at that time.
The spring force will overcome the solenoid force for a short period of time, twice per period, because the magnetic force generated by the solenoid is proportional to the current flowing through its coil. This problem manifests as a vibration of the armature, resulting in a humming sound and causing stress on the solenoid valve. The coil around the armature is shielded with a simple conductive ring called a shading ring to avoid this problem. Copper is usually used for this purpose. Shade rings store magnetic field energy and release it with a 90° phase difference.
As the primary coil’s magnetic field decreases towards zero, the shading ring’s magnetic field increases, covering the gap between the amplitudes of magnetic fields during zero crossings and preventing vibrations. Shade rings are built into most solenoid valves that can be used with various coil voltages.
It is possible that the shading ring will be ineffective if dirt accumulates around the armature. One solution is to use an electronic circuit that filters the solenoid current so that there are no zero-crossings. External circuitry can be built on top of the solenoid valve coil, or the circuitry can be embedded into it. Typically, it is implemented using rectifier diodes and a filtering capacitor in a full-wave rectifier topology.
There are so many solenoid valve manufacturers are present in the valve market. Be careful while selecting an accurate solenoid valve manufacturer who offers a huge range of solenoid valves. The aira Euro automation is one of the well-known and trusted solenoid valve manufacturers and exporters.