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What is a Solenoid Valve and How Does it Work?

Butler & Land Technologies, as a renowned solenoid valve distributor, knows more about how a solenoid valve operates than most. That’s why we’ve set out to address some of the most often asked questions regarding solenoid valves, including how they work, how they’re used, and how to repair them. View our ASCO Valves.

Solenoid Valve Info

Table of Contents

What is a Solenoid Valve?

An electromagnetic actuator (solenoid) and a valve body make up a solenoid valve, which is an on/off electromechanically actuated valve. The valve actuator is the solenoid-plunger assembly, which opens and closes the valve. This actuator can be configured so that the plunger motion is limited to either opening or closing. Because there is no intermediate or in-between position, a solenoid cannot throttle flow. The pressure containing elements in contact with the process fluid make up the valve body.

To control the flow of liquid or gas, a solenoid valve is often used. There are several varieties of solenoid valves, but the two most common are pilot operated and direct acting. The most common type of pilot controlled valve uses system line pressure to open and close the main orifice in the valve body. Directly driven solenoid valves open or close the main valve orifice, which is the valve’s only flow route. They’re used in systems that require low flow rates or have a low pressure difference across the valve orifice.

Related: ASCO Valve Terminology & Functions

Types of Solenoid Valve Operations

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.

Internally Piloted Solenoid Valves

Internally piloted solenoid valves are used for high flow rate and high pressure applications. The pressure across the valve opens or closes this type of valve. An orifice, also known as an equalizing hole, is used to accomplish this. The standard design involves the orifice’s core blocking flow. The fluid passes through the orifice when the valve is closed, and pressure builds on both sides of the diaphragm. Due to the larger effective area on top of the diaphragm, a shut-off force is created as long as fluid flow is blocked. When the valve is opened, the core opens the orifice, releasing pressure from the diaphragm’s top. The valve is then opened by the line pressure.

Externally Piloted Solenoid Valves

The valve is actuated by an independent pilot medium in these types. The valve seat is closed in the unpressurized state. The independent pilot medium is controlled by a 3-way solenoid valve that can be mounted on the actuator. The piston is raised against the action of the spring when the solenoid valve is energized, and the valve opens. If the spring is placed on the opposite side of the actuator piston, a normally-open valve is obtained. The independent pilot medium is connected to the top of the actuator in these cases. There is no spring in the double-acting versions controlled by 4/2-way valves.

Solenoid Valve Components

All materials used in the construction of the valves are carefully selected according to the varying types of applications. Body material, seal material, and solenoid material are chosen to optimize functional reliability, fluid compatibility, service life and cost.

Coil

The coil, which is made up of an insulated copper wire wound tightly around a core tube, is one of the main components of the solenoid. When current is applied, a magnetic field is created, as previously stated.

Core

The core of a solenoid, also known as the armature or plunger, is the moving part. This is a soft magnetic metal, which is a ferromagnetic metal that can be magnetized and demagnetized easily at low magnetic fields. The core is attracted to the coil when it is energized, generating a magnetic field, which opens or closes the valve.

Core Spring

When the magnetic field is removed, the core spring returns the core to its original position. Depending on the valve operation, the core spring design and configuration in the solenoid assembly varies. There are some designs that do not use springs to create a return action, such as latching type solenoid valves.

Core Tube

The coil is wound in the core tube. This also serves as a soft magnetic core, which boosts the coil’s magnetic flux.

Fixed core

This is attached to the core tube’s closed end, which improves the magnetic flux. In addition, the material is a soft magnetic metal.

Diaphragm

The solenoid assembly is isolated from the fluid by the diaphragm, which is a flexible material. The diaphragm’s purpose is to keep the fluid pressure in check.

Stem

The stem is the part of the valve that holds the core or plunger. The stem moves along with the core as it is attracted by the coil, actuating the valve.

Disc

When the valve is closed, the disc stops the flow of fluid. Instead of a disc, diaphragms, bellows, or pinch devices are used to block fluid flow in some solenoid valve designs. The disc is usually made of corrosion and erosion resistant materials like PTFE or stainless steel, depending on the application.

Seat

When the valve is closed, the seat is the orifice that presses against the disc. Depending on the valve design, the seat may or may not be present. Corrosion and erosion-resistant material is also used for the seat. The valve will become passing and unable to stop flow once the seat or disc has been damaged.

Seal

The seal, like the diaphragm, keeps the fluid away from the solenoid assembly and the outside world. Seal materials such as PTFE, FKM, NBR, and EPDM are available depending on the application and the process fluid.

Bonnet

The valve bonnet is attached to the valve body at the top. The stem and core tube of the valve extend through the bonnet.

Body

The diaphragm, disc, seat, and inlet and outlet ports are all housed in the body of the valve.

Bleed Orifice

A bleed orifice is installed on the diaphragm for indirect or semi-direct acting solenoid valves. An equalizing hole is used in some valve designs. The bleed orifice allows the valve to open or close by using line pressure.

Pilot Channel

A pilot channel is built into the valve body for indirect acting solenoid valves. This is the point at which fluid flows from the diaphragm’s top to the downstream side of the valve.

Circuit Functions of Solenoid Valves

Solenoid valves are used to close, open, dose, distribute or mix the flow of gas or liquid in a pipe. The specific purpose of a solenoid valve is expressed by its circuit function.

Two-way Solenoid Valves

This type of solenoid valve is used to block or allow fluid flow and has one upstream and one downstream port. The solenoid valve can be configured as either normally open or normally closed; normal state refers to the state when the solenoid valve is de-energized. When de-energized, a normally open valve opens, and when energized, it closes. In the case of normally closed valves, the opposite is true.

Three-way Solenoid Valves

A 3-way valve has three connection ports. Typically, it has 2 states (positions) it can be in. So, it switches between two different circuits. These are used to apply and exhaust pressure from an actuator or downstream equipment in a controlled manner. With the addition of a universal function, three-way solenoid valves can be configured as normally open and normally closed. Fluid flows from the inlet port to the outlet port when a normally open three-way valve is de-energized, while the exhaust port is closed. The inlet port closes when the device is turned on, and the outlet port connects to the exhaust port. In the case of normally closed valves, the opposite is true. On the other hand, the universal function is used to select the flow direction from one port to another.

Solenoid Valve Materials

Bronze Valves

Bronze is a copper and tin alloy. Bronze is more corrosion resistant than cast iron and has a higher resistance to cracking.

Brass Valves

Brass is a copper and zinc alloy. Compared to bronze, brass is more corrosion resistant, durable, and malleable.

Cast Iron Valves

Cast iron is extremely strong, but due to its low ductility, it is prone to cracking.

Stainless Steal Valves

Even at high operating temperatures, stainless steel offers high corrosion resistance, strength, and durability. However, unless a higher grade of stainless steel is used, chloride ions can corrode stainless steel.

Types of Construction For a Solenoid Valve

Polytetrafluoroethylene (PTFE)

Thermoplastic fluoropolymer polytetrafluoroethylene (PTFE) is chemically inert to most substances. The hydrophobic properties of this material make it ideal for ultra-clean and chemical applications.

Polyamide (PA)

Polyamide (PA) has mechanical properties similar to PVC and is salt water resistant.

Polypropylene (PP)

Polypropylene (PP) is a thermoplastic with mechanical properties similar to steel and brass, but with better acid, salt, and alkali resistance.

Polyphenylene Sulphide (PPS)

PPS (Polyphenylene Sulphide) is a high-temperature polymer with excellent acid and alkali resistance.

Polyvinyl Chloride (PVC)

PVC is suitable for use in seawater, but it lacks the strength and temperature resistance of brass and copper.

Polyvinylidene Fluoride (PVDF)

Molding and welding Polyvinylidene Fluoride (PVDF) is simple. This material is also acid and alkali resistant, but it is not suitable for high-temperature applications.

Where is a Solenoid Valve Used?

To operate and provide control, every valve requires a power source. This power source for a control valve could be a solenoid, a pressure pilot, or an electric pilot if you have an electric actuator.

General on-off control, plant control loops, process control systems, and various original equipment manufacturer applications are just a few of the industrial settings where solenoid valves are used. View more below.

  • Water supply
  • Treatment of drinking water
  • Waste water treatment
  • Purification/ treatment of grey and black water
  • Machine and plant engineering
  • Cooling, lubrication and dosing
  • Building services
  • Large heating systems, climate control
  • Safety engineering
  • Water mains protection and fire extinguishing systems
  • Compressors
  • Pressure relief and drainage
  • Fuel supply
  • Transport and tank facilities
  • Firing systems
  • Oil and gas burner control
  • Gas chromatography
  • Gas mixture regulation
  • Blood analysis instruments
  • Control of cleaning processes

Where To Buy a Solenoid Valve

Contact Butler & Land Technologies 

Solenoid Valve FAQ

Most frequent questions and answers about Solenoid Valves

The definition of a solenoid valve is an electro-mechanical valve that is commonly employed to control the flow of liquid or gas. There are various solenoid valve types, but the main variants are either pilot operated or direct acting.

Solenoid valves are control units which, when electrically energized or de-energized, either shut off or allow fluid flow. The actuator takes the form of an electromagnet. When energized, a magnetic field builds up which pulls a plunger or pivoted armature against the action of a spring.

Solenoid valves are the most frequently used control elements in fluidics. They are commonly used to shut off, release, dose, distribute or mix fluids. For that reason, they are found in many application areas.

Common uses. Solenoid valves are used in fluid power pneumatic and hydraulic systems, to control cylinders, fluid power motors or larger industrial valves. Automatic irrigation sprinkler systems also use solenoid valves with an automatic controller.

A solenoid valve is an electrically controlled valve. The valve features a solenoid, which is an electric coil with a movable ferromagnetic core (plunger) in its center. In the rest position, the plunger closes off a small orifice. An electric current through the coil creates a magnetic field.

Most solenoids unscrew counter-clockwise to remove. If the plunger doesn’t move easily and smoothly, replace the solenoid; it is damaged and can’t be repaired. Do not apply any oil or lubricant to the solenoid plunger, if it is sticking it is not repairable, replace it.

The quickest way to test the solenoid valve is to apply a charge directly to it. There are two wires which cross directly above the valve as it lays in the timer that you will touch with a multimeter. This should send a charge onto the valve, and if it is functioning normally, it will open.