Valve

SOLENOID VALVE

Posted on by ATC

WHAT IS SOLENOID VALVE

A solenoid valve is an electro-mechanical device used to control the flow of fluids. They consist of two main components, the valve body and a solenoid, which has an inductive coil and a movable ferromagnetic core in its center. Solenoid valves are used to control clean fluids as they are sensitive to dirt. They work to either open, close, dose, or mix a fluid medium with two or more inlets/outlets.

At rest position, solenoid valves are either normally open (NO) or normally closed (NC). When there’s no current in the coil, the NO valve is open while the NC valve is closed. Once the coil is energized, a magnetic field is created, exerting an EMF (electromagnetic force) on the plunger, which overcomes the spring force and causes the plunger to either close the orifice for NO valves or open the orifice for the NC valves.

SOLENOID VALVE WORKING PRINCIPLE

How a solenoid valve works is by controlling the flow of liquids or gases in a positive, fully-closed or fully-open mode. They are often used to replace manual valves or for remote control. Solenoid valve function involves either opening or closing an orifice in a valve body, which either allows or prevents flow through the valve. A plunger opens or closes the orifice by raising or lowering within a sleeve tube by energizing the coil.

Solenoid valves consist of a coil, plunger and sleeve assembly. In normally closed valves, a plunger return spring holds the plunger against the orifice and prevents flow. Once the solenoid coil is energized, the resultant magnetic field raises the plunger, enabling flow. When the solenoid coil is energized in a normally open valve, the plunger seals off the orifice, which in turn prevents flow.

SOLENOID VALVE COMPONENT

  1. Coil: This is the electrical part of the valve consisting of a wound of the insulated copper wire creating a magnetic flux when energized. This coil is placed on the tube with retaining clips.
  2. Solenoid Enclosure: Metal housing around the coil for electrical or mechanical protection is call solenoid enclosure. This protects the coil against the entrance of water or duct.
  3. Core Tube: Stainless steel tube that is closed at one end is installed to improve the magnetic flux of the coil upon energization.
  4. Retainer Clip: This is the clip anchoring the coil to the YOKE.
  5. Plugnut:  This is the stationary part of the solenoid valve that helps to press the core tube in the closed-end to improve magnetic flux.
  6. Core: This is the soft magnetic plunger part of the valve that moves by magnetic force.
  7. Core Spring: This is a retractable part of the Solenoid valve which helps the core to keep in a fixed position when the coil is not energized.
  8. Rocker: This is the moving part serving to open and close the ORIFICE for the passage of fluid.
  9. Body: This is the main part of the valve with all ports and main seats fitted inside it.
  10. Manual Operator: This for the manual operation of the solenoid valve to open or close the orifice. This acts as a solenoid valve manual override button to control the flow.
  11. Diaphragm: This is isolating the fluid from the control system with help of seal-tight assembly.
  12. Cover: This is mounted on the valve body and incorporating a  number of Orifices.

      13+ 14 . Orifice: This is the flow path of fluid transmission in the valve body.

  1. Manual Operator Spring: This is actually the part of the Solenoid    valve that helps to ensure the drawback of the spring to its initial position.

TYPES OF SOLENOID VALVE 

Direct Acting Solenoid Valves

The components of direct acting (direct operated) solenoid valves have a simple working principle. With no power, the plunger blocks the orifice with the valve seal for a normally closed valve. This closure is being forced by the arrival of a spring. When power is applied to the coil, an electromagnetic field is created, which attracts the plunger upward and overcomes the spring force. This allows the media to flow freely through the orifice. A normally open valve has the same components as a normally closed valve, but it operates in the opposite direction.

The orifice diameter and magnetic force of the solenoid valve are directly related to the maximum operating pressure and flow rate. As a result, direct acting solenoid valves are typically used for low flow rates. Direct-operated solenoid valves do not require a minimum operating pressure or pressure difference, so they can be used at any pressure from 0 to the maximum allowable pressure.

Pilot Operated Solenoid Valves

In the Pilot solenoid valve, the plunger act according to differential pressure. Pilot-operated directional control valves require less electrical energy to work to keep up full power with specific flow control. This type of valve performs at a slower rate than a direct-acting solenoid valve.

This uses a solenoid diaphragm for flow control with pilot control using a small chamber directly above the diaphragm that helps in the operation of the valve. Process fluid is allowed to enter the chamber through a small orifice that compresses against the diaphragm and forces the seat to maintain the closing seal.

Once current is applied to the pilot solenoid, the diaphragm is being pulled upwards against the spring force. The process fluid in the chamber is forced back through the orifice towards the inlet port where it merges with the main flow through the vale body.

Main Features of Pilot Operated Solenoid Valve

  • The valve is sealed by the diaphragm.
  • It utilizes the energy of the streaming fluid to open and close.
  • This type of valve needs opening and closing with minimal differential pressure known as “minimum working pressure”. This pressure varies from 0.1 to 1 bar, depending on the dimension of the valve.
  • The same size of the coil can be used for the operation of valves with different dimensions because the diameter of the pilot seat remains the same for different dimensions of valves
  • The flow direction for the valve is given.

SOLENOID VALVE BASIC DESIGN AND FUNCTION

Solenoid valves have a control unit which is when electrically energized or de-energized this acts either to shut off or allows fluid flow. The actuator of a solenoid valve acts as an electromagnet. When energized, a magnetic field is generated which pulls the plunger against the action of the spring while the de-energized plunger returns to its original position.

The basic design of a solenoid valve can be divided into two categories:

  1. Solenoid Operator and
  2. Valve body part

The solenoid Operator part of the valve is basically an electrical circuit that helps to move the plunger of the valve by generating a magnetic field when an electrical current is passing through this. There are basically 06 parts of this complete circuit

  • Core
  • Solenoid Coil
  • Solenoid encloser
  • Core tube
  • Plugnut and
  • Retainer clip

The valve body is basically the operation part of the valve that controls the fluid flow according to the application of electrical current in the solenoid operator. This part of the valve contains 08 sections to act together for flow control

  • Rocker
  • Core
  • Core spring
  • Manual operator
  • Diaphragm
  • Cover
  • Orifice and
  • Manual Operator spring

The function of each part is covered in the above section (Parts Name and Terminology for Solenoid valves) of this article.

ADVANTAGES AND DISADVANTAGES OF SOLENOID VALVE

Solenoid valves are used in every industry due to their versatility of this valve. The solenoid valve can be used for either Liquid or gas transportation in the piping system. Its electromechanical magnetic nature makes the valve a reliable option for pneumatic and hydraulic systems.

Advantages of the Solenoid valve

Solenoid valves have a large number of advantages that are gained by improved design over the years that makes the valve safer and efficient. The solenoid valve can adapt and be installed in a number of locations making the valve versatile for many applications. some advantages of solenoid valve are as described below:

  • Quick responsive
  • Low power consumption
  • Remote operation
  • Fits in a variety of machinery and applications
  • Cheap replacement parts
  • Compatible with both AC and DC power supply
  • Low and High-temperature usage
  • Safety external leakage block
  • Can be installed vertically or horizontally
  • Disadvantages of the Solenoid valve

Disadvantages of Solenoid valve

Like every other valve solenoid valve also have some disadvantages that make this valve with some error.

 disadvantages of solenoid valve are as follows:

  • Sensitive to voltage change
  • The valve can partly close if the magnetic field isn’t set up correctly
  • The coil may need to be replaced over the lifetime of the valve
  • Control signal must stay on during operation
  • Valve fluid can be affected by the flow (pre-valve flow is always greater than the backflow of the valve)
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