When a solenoid coil voltage (DC or AC voltages such as 230V, 110V, 24V, 12V) is applied, the coil becomes an electromagnet and generates a magnetic force. This force allows the core inside the valve to move. According to this action, the valve opens or closes. If the fluid does not pass while there is no energy, the shape is normally closed, When the fluid passes without energy, the shape is normally open.

Read More: Types of Solenoid Valves

As shown in the figure, when the coil is energized, the orifice through which the fluid flows is directly closed or opened directly. Take the name of the direct acting here.

As can be seen, opening and closing of Pilot Operated solenoid valves is done using line pressure with a control panel. The fluid in the line fills the upper section of the diaphragm, closing down the main hole with the line pressure and spring pushing downwards. When the solenoid coil is energized, it pulls the core upward to open the control hole and the fluid is transferred to the outlet of the line via the fluid discharge hole on the diaphragm. The diaphragm lifts upward as pressure on the diaphragm is lifted.

Solenoid valve is divided into 2 main groups in terms of working principle in general.

  • Direct acting solenoid valves
  • Pilot operated solenoid valves

How do direct acting solenoid valves work?

Direct acting solenoid solenoid valve consists of valve body, tube, core, coil, o-ring, knurled nut and socket.

The direct acting solenoid valve body is first connected to the pipeline in the direction of flow of the fluid (in the direction of the arrow on the body). Sealing is provided by the o-ring in the sleeve fitting part and the sealing element in the core under the core.

Read More: Applications of Solenoid Valves

If the solenoid valve connected to the pipeline is normally closed (N.C.) type (does not pass the fluid without electricity), the valve position must be changed so that the fluid flows to the other outlet side. So N.C must be N.O. (normally open). The only requirement is that the coil on the solenoid valve is powered by electrical energy in the voltage range written on it. When the coil is energized with the correct energy (+/- 10.15% fault), it will pull the nucleus (core) in the tube. When the core which pressing the orifice in the valve body moves upwards, the fluid that is waiting at the entrance of the orifice will be opened. Then, the fluid that opens will continue to pass through the outlet of the valve. This continues until the electricity on the coil is cut off. When the electricity supply is cut off, the coil releases the core. The core closes with its own weight and the spring force on it again by pressing the orifice on the body. Fluid flow is stopped. The solenoid valve returns to its first position in the N.C (normally closed) position.

In the direct draw solenoid valve, the diameter of the orifice in the valve body is very important. It can be opened up to a diameter that will drain as much as it needs. But it can be up to 9 mm, at least 1 mm diameter. The diameter of this orifice also affects the valve working pressure. While orifice grows as the coil power is the same, the valve working pressure drops.

How do pilot operated solenoid valves work?

Pilot operated solenoid valves can also be called diaphragm solenoid valves. Valves with large orifice diameter in valve body. They are manufactured in 3/8 “, 1/2”, 3/4 “, 1”, 11/4 “, 11/2”, 2 “, 3” dimensions as the connection size. The diameter of the orifice starting from min. 12 mm can be up to 80 mm. We can not provide the sealing of this large orifice with the “sealing element on the core”. The solution is to provide leakproofness with diaphragm.

How will you lift the diaphragm and the orifice will open and the fluid will pass to the exit side? The answer to this question is the most important point of pilot controlled solenoid valve operating principle.

Pilot control means that the equal pressure existing on the diaphragm that provides valve sealing creates a differential pressure in a certain way and this differential pressure moves the diaphragm upwards. Thus, the orifice will open, the valve will change position and the fluid valve will pass to the outlet side.

Differential pressure is usually min. expected 0.5 bar, 0.3 bar. It is expected that the fluid which will pass through the valve for the formation of the differential pressure should be like the input pressure min.0.5 bar and max.10 bar, 16 bar, 30 bar, 40 bar, 70 bar.

So how is the “differential pressure force” that the solenoid valve needs to change its position?

In the solenoid valve, the diaphragm closes the solenoid valve orifice to trap the fluid between the solenoid valve body cap and the body. (There is a 1mm diameter hole in the center of the diaphragm, which fills the bottom of the diaphragm, from above this opening into the top of the diaphragm and into the barrel, and presses on the upper surface of the core, closing the hole of the small bypass orifice on the chamber lid). When the diaphragm is filled with liquid at the top and bottom, the diaphragm remains in a balanced pressure environment.

When the solenoid valve coil acting on the tube-core group on the cap is energized, the core in the tube will move up. When moving upward, liquid between the diaphragm and the cap flushes through the orifice through the 1mm hole on the diaphragm, through the valve in the cap on the valve body, and discharges to the valve outlet side. The pressure on the diaphragm drops as the fluid above the diaphragm moves to the outlet side of the valve. The pressure under the diaphragm is still the same fluid pressure. Since the hole on the diaphragm is small, liquid flows through this hole and fills up on the diaphragm, which takes time to compensate the pressure. If the pressure balance on the diaphragm deteriorates before this time period, the pressure under the diaphragm will push the diaphragm upward easily and adhere to the ceiling of the lid. In this case, the orifice will be opened and the valve will change position, so the fluid will move smoothly through the orifice and towards the exit side.

This is where the pressure should be min. 0.5 bar to lift the diaphragm so that the valve position changes. This is how the valve works with differential pressure.

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