Control Valve

Various types of Solenoid valves and their schematics

What is a solenoid valve?

This type of valve is used when we need to control the flow of the fluid automatically, these valves are mostly used in many industrial applications. Solenoid valves can be controlled by electric current these valves are called a two-position device due to the fact that they could be either all the way in or all the way off. These valves are capable to be operated in AC or DC voltage. The solenoid valves would utilize the electric power to open and close the orifice in the valve body, and thus the flow can be prevented or allowed according to the need.

How does a solenoid valve operate?

When electric current passes through the solenoid coil then the coil would get energized and a magnetic field will be created and this would pull the armature up. So when the armature moves up then the valve plug would be lifted off the valve seat and thus it would allow the fluid to pass. The weight of the valve stem, disc, and plunger would be useful for the closing action of the control valve.

These valves utilize pneumatic and electrical energy and it can be called an electro-pneumatic converter. So basically these valves would have the electrical switching part called the solenoid and the pneumatic valves as the signal output medium.

What are the types of solenoid valves?

The normally open and normally closed in a solenoid valve indicates the valve’s condition when the power is off.

2-way solenoid valve

2-way solenoid valve operation

In this type of valve, it would have two orifices and it could be normally open or normally closed.

2-way normally closed

This type of valve would have one inlet and one outlet and it would stay in a closed position if not energized. If it is energized then it would open and thus flow would take place, this type of valve is mostly used to permit the flow.

2-way normally open

This type of valve would have one inlet and one outlet, so the valve would stay open if it is not energized. So if the flow must be stopped then it needs to be energized and this valve would allow the flow even when the system power is off.

Schematic of 2-way solenoid valve

2-way solenoid valve schematic

3-way solenoid valve

This type of valve would have three port connections and two valve seats.

3-way solenoid valve operation

3-way normally closed

This type of valve would have an inlet, outlet, and exhaust ports. So when this valve is unenergized the outlet port will be connected to the exhaust port. When they are energized then the inlet port will be connected to the outlet port.

3-way normally open

This type also has the inlet, outlet, and exhaust port. So if this is not energized then the inlet will be connected to the outlet. While these valves are energized then this valve would connect the outlet to the exhaust.

3-way universal

This type of valve would have three ports, one of the ports would act as an inlet or outlet and it would be connected to one of the other two ports when it is energized/unenergized. We can use this type of valve to divert the flows or to select alternating sources.

Schematic of 3-way solenoid valve

3-way solenoid valve schematic

4- way solenoid valves

4-way solenoid valve operation

The four-way solenoid valves are mostly used when double-acting cylinders are required to operate. Mostly these valves would have four or five ports, one pressure, two-cylinder, and one or two exhausts. In the above image when the power is off the flow would take place from the compressor P and it would go out through B. The air would flow back from the cylinder through port A, and out through the exhaust port EA.

When the power is ON, the flow would take place from the compressor to P, and it would go out through A. The air would flow back from the cylinder through port B and out through the exhaust port EB.

Direct-acting solenoid valve

In this type of solenoid valve, all the flow would pass through an orifice which will be opened by an electromagnet or a plunger. In this type of solenoid valve, the seat seal will be attached to the solenoid core. When this valve is energized the seat orifice would open, if it is not energized then the seat orifice would stay close.

Pilot operated solenoid valve

Operation of the pilot of pilot operated solenoid valve

In this type of solenoid valve the actuation is done by using the pressure of the fluid, these valves could be either piston or diaphragm type and it would need differential pressure in order to keep the valve closed. This type of solenoid valve has a quick response time and they are economical too. The solenoid size can be kept minimum by using the pilot control and due to this, there could be two advantages such as reduced power consumption and also the generation of heat. Pneumatically the valve switching would be positive, the electrical signal which is applied to the solenoid would actuate the pilot valve armature. The main valve would be operated by the pilot valve signal.

Double solenoid valve

In this type of solenoid valve, the spring return would be replaced by a second solenoid. The characteristics of this type of valve would be different from the spring return type. The double solenoid valve would remain in its last switching position, even when the power is removed from both the solenoids, till an opposing signal is applied to it.

4/2 way solenoid valve

Proportionating valve

In this type of solenoid, valve we could do complete and continuous fluid control. In order to achieve the full range of valve position, an analog signal will be sent.

What are the major components of a solenoid valve?

Specific parts of proportional solenoid valves

Solenoid valve symbols

Two way Two Position Solenoid valve symbol

2/2 solenoid valve symbol

Three-way Two-position Solenoid valve symbol

3/2 solenoid valve symbol

Four-way Two Position Solenoid valve symbol

4/2 solenoid valve symbol

How to wire a solenoid valve?

The solenoid valve mostly would have three wires, one of them would be the ground wire and the other two are phase and neutral. In order to operate the solenoid, we need to give supply to it. The solenoid could be AC or DC, mostly it would be AC, so connect the solenoid valve to the power supply and we should connect the phase and neutral if it is AC. During certain cases, there won’t be any wire polarity, and so there would be a common and a trigger wire. In case if you have more solenoids then you should take each wire from all the solenoids and link them as common.

The supply should be given according to the coil rating, if it’s 220v then we should give the 220v supply. So if we need to connect the solenoid valve to the controller, then we can see the common and trigger feed section in the controller so connect the solenoid valve cables to it. If we have two solenoids or more than that then, we should take the wires from each of the solenoids and connect as common as we discussed earlier then it can be connected to the controller. We must check if the wires from the solenoid valve are properly put into the terminal strip of the controller.

How to select a solenoid valve?

  • We should consider the valve type like two way, three-way, or four-way
  • Voltage required
  • Pressure and temperature range
  • Response time of the valve
  • The medium which is to be handled must be considered
  • Port size fluid connection
  • De- energized position must be considered like normally open or normally closed.
  • Coil connection type
  • Type of electrical enclosure
  • Duty cycle must be considered like continuous or intermittent
  • Minimum or maximum operating pressure differentials
  • The diameter of the orifice should be considered
  • We must also consider the allowable internal leakage

What are the advantages of a solenoid valve?

  • It can be used to shut release or distribute the fluid
  • Fast and safe switching
  • High reliability
  • Good service life
  • Compact design
  • Low control power

What are the applications of solenoid valves?

  • It is used to control the hydraulic action
  • Compressors and vacuum pumps
  • Plastic molding machinery
  • It can be used for the mixing and distributing of the air
  • Boilers
  • It can be used in an RO purifier
  • Sprinklers and fire fighting systems
  • It is also used in dust collectors


post-graduate in Electronics & communication.

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