Control Valve

What is a solenoid valve and what are its types

What is a solenoid valve and what are they used for

A solenoid is a coil that would create a magnetic field, only if it is covered by a core or any magnetic object. The solenoid controls the solenoid valve and this valve is used to control the flow of water or air as a switch. The opening of the valve would take place if the solenoid is active and if the solenoid is inactive the valve would stay close. These valves are electromechanical and they have been used to control the gas and liquid flow. Solenoid valves are found in many applications and are commonly used in refrigeration and air conditioning systems, their function is very simple to turn the refrigerant flow on and off. These valves can be considered as electro-pneumatic relays. The pneumatic output is based on electrical input. Solenoid valves are the interface between the electronic control system and pneumatic power. Electric current is used to control the solenoid valve. They are called a two-position device because either they are all the way on or all the way off. The operation of these valves can take place either in AC or DC voltage.

What are the parts of the solenoid valve

A solenoid valve consists of a valve body, a magnetic core that is attached to the stem and disc, and a solenoid coil. A spring is used to release and close the valve.

Solenoid – it is an electric coil and has a plunger or core in its center and the core is coaxial with the solenoid. This coil is of copper wire

Core – Core is called as a plunger and it is a magnetic component that moves when the solenoid is energized

Valve body – The valve body is selected so that it must be compatible with the fluid, it is mostly made up of brass, stainless steel, and aluminum.

Spring – In order to release and close the valve spring is used

Bonnet – A threaded nut or square flange that secures the magnetic operator assembly to the valve body

Seat seals – Usually it is mounted on the MP, it is used to close the orifice of the valve or pilot

Why do we need solenoid valves

These valves are used if we need to control the flow of fluid automatically. Solenoid valves are widely used in many chemical processing industries. Solenoid valves are devices that can convert electrical power to mechanical force and motion. They are also used in many hydraulic circuits as the solenoid-operated direct control valves and they are used to change the flow direction in a hydraulic system. Solenoid valves are mostly used for on-off operations that need very high speed of response, solenoid valves are capable to open or close in 8-12 milliseconds.

What is called a solenoid

A solenoid is an electric coil and in its center, there will be a movable electromagnetic core. This core is known as a plunger in the rest position the plunger closes off a small orifice. If we pass an electric current through the coil then it would create the magnetic field and a force will be exerted in the plunger by the magnetic field, because of this the plunger will be pulled towards the center of the coil and the orifice will open. This principle is used in the solenoid valve. This device is capable of linear motion and they can also be considered as an actuator. A liner force will be produced by the solenoid if energy is given to it.

How solenoid valves are constructed

The coil of the solenoid valve is made up of copper wire. An insulation layer is used to separate the layers of wire and varnish is used in the coil so that it won’t be affected by solvents or other moisture. Laminated sheets are used to make the frame of the solenoid and it would be magnetized when the current pass through it. Solenoid plunger is not a stator device it is behind the mover mechanism of the solenoid the plunger is made up of steel laminations. In a solenoid valve there would be cover it could be either over the solenoid or the entire valve.

How does a solenoid valve work

An electric current will be passed through the solenoid coil and it would create a magnetic field this field would pull the plunger close to the center of the coil and this would make the orifice open. That’s how the solenoid valves convert electrical energy into mechanical energy and this mechanical energy is used to open or close the valve. Metal or rubber seals are used, and it could also have an electrical interface for easy control. Spring is also used in a solenoid valve to keep the valve in an open or closed position while the valve is in the closed position. Constant current is needed for the valve operation so that it can remain open. If there is no current then the valve would return to its original position.

What are the types of a solenoid valve

Pilot operated valve

In this type a pilot control is used, so the size of the solenoid can be kept minimum and because of this the power consumption is decreased, this will also reduce the heat generation. In pilot operated solenoid valve, the electrical signal is applied to the solenoid, this would actuate the pilot valve and the pilot actuates the main valve. Pilot operated valves can be piston or diaphragm type and to keep the valve closed it needs differential pressure. These valves have quick response time and they are not costlier.

Direct-acting solenoid valve

In a direct-acting solenoid valve, a plunger will open and close the valve. These valves have low flow rates and high differential pressure drops. The direct operated type has a quicker response than a pilot operated type.

Two-way solenoid valves

In two way solenoid valves it has one inlet and one outlet pipe connection. They are either closed construction valve, so they would be closed when de-energized and opens when energized or it could be normally open construction valve, so it would close when energized and open’s when de-energize

Three-way solenoid valves

In this type of solenoid valve, it has three pipe connections and two orifices, so if one is open the other one is closed. These valves have three modes of operation the first one is normally closed construction in this type the pressure port is closed and the exhaust port is connected to the cylinder port with the valve energized, the pressure port is connected to the cylinder port and the exhaust port is closed.

In normally open construction if the valve is de-energized then the pressure port is connected to the cylinder port and the exhaust port is closed. The pressure port is closed if the valve is energized and the cylinder port is connected to the exhaust port. The next type is universal construction and this would allow the valve to be connected in either normally closed or normally open position.

Four-way solenoid valves

These valves are mostly used to operate double-acting cylinders. These valves have four or five pipe connections one pressure, two-cylinder, and one or two exhausts. In one valve position, the pressure is connected to one single port and the other is connected to the exhaust. In other valve position pressure and exhaust are reversed at the cylinder connection.

How to select a solenoid valve

  • Valve type must be determined as if it is two, three or four-way
  • Voltage and pressure
  • Medium handled
  • Materials that are used for construction like brass, plastic…
  • Port size fluid connection
  • De-energized position as if it is normally open or close
  • Coil and connection type
  • Current draw limitations
  • Electrical enclosure type
  • Duty cycle and life expectancy
  • Life expectancy
  • Maximum and minimum operating pressure differentials
  • Orifice diameter
  • Allowable internal leakage

What are the advantages of solenoid valves

  • Solenoid valves can do the quick operation, these valves can open and close very quick
  • Solenoid valves have high reliability
  • Automatic fluid flow control
  • Solenoid valves have a good service life
  • These valves are compact in design and have limited pressure drop

What are the disadvantages of solenoid valves

Durability is very low when it is compared to an electric motor

What are the applications of the solenoid valve

  • Solenoid valves are widely used in many industrial and civil applications, they are chosen in the field that needs compressed air and liquid
  • These valves are built for remote control, because of this they are used in automatic irrigation control system
  • Solenoid valves are used in many chemical industries, construction works, and air conditioning facilities
  • Solenoid valves are used in certain household types of equipment like washing machines, refrigerator, and in water supply
  • Food processing machinery
  • Dentist equipment
  • Coffee machines and boilers
  • Sprinklers and fire-fighting systems
  • Compressors and vacuum pump
  • Suction applications
  • Temperature control of separate units in multiple systems

What are the specifications of the solenoid valve

  • Valve type – 2 way
  • Action – Direct acting
  • Orifice – 5.0mm
  • Operating pressure – vacuum to 50PSI
  • Port size – 3/8OD tube, 3/8 push-in fitting, 3/8 female NTP
  • Voltage – 12-24V DC, 220-240V AC (50/60Hz)
  • Voltage tolerance – +/-10% of specified voltage
  • Coil power – 20W
  • Electrical connections – Molded cable, ATEX explosion proof
  • Service – Air, water, liquid

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post-graduate in Electronics & communication.

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