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What are the Parts of Solenoid Valves: Full Guide
A solenoid valve is an electromechanical device used to control the flow of liquids or gases in a system. It works by converting electrical energy into mechanical movement through an electromagnetic actuator called a solenoid. When electric current passes through the coil, it generates a magnetic field that moves a plunger, which opens or closes the valve’s internal flow path.
Structurally, a solenoid valve consists of two major assemblies:
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The solenoid actuator converts electrical energy into motion.
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The valve body controls the fluid flow.
Inside these assemblies are several internal components that work together to ensure precise and reliable operation. Understanding these components helps engineers select the right valve, diagnose faults, and maintain long service life.
This article will focus on the main components of solenoid valves. Keep reading
Components of Solenoid Valves
Although solenoid valve designs may vary depending on the valve type, most share a similar internal structure. The main components include the coil, plunger, springs, diaphragm, valve body, seals, and orifice, along with several supporting parts that ensure smooth operation and reliable sealing.
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Coil (A)
The coil is the electromagnetic component that powers the solenoid valve. It is typically made from insulated copper wire wound around the outer section of the solenoid tube or magnetic core. When an electrical current passes through the coil, it generates a magnetic field that creates an attractive force on the plunger inside the valve. This electromagnetic force converts electrical energy into linear mechanical motion, allowing the valve to open or close automatically.
Coils are designed to operate on either AC or DC power, depending on the valve specification. To protect the windings and improve durability, the coil is usually encapsulated in insulating materials such as epoxy resin or thermoplastic housing. This protects the coil from environmental factors such as moisture, vibration, and temperature fluctuations. Because the coil is responsible for generating the magnetic force needed to move the plunger, its design directly influences the valve’s response speed, reliability, and energy consumption.
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Spring (B) and Plunger (C)
The plunger, sometimes called the armature or piston, is the main moving component of the solenoid valve. It is typically a cylindrical piece made from ferromagnetic material, such as magnetic stainless steel or soft iron, allowing it to respond to the magnetic field generated by the coil. The plunger moves vertically inside the solenoid tube and directly controls the opening or closing of the valve.
Working together with the plunger is the return spring, which provides a mechanical force that determines the valve’s default position. When the coil is not energized, the spring pushes the plunger back to its original position.
In a normally closed solenoid valve, the spring pushes the plunger downward to seal the orifice and stop fluid flow. In contrast, a normally open valve uses the spring to hold the plunger upward, allowing fluid to pass when the coil is not powered.
The interaction between the spring force and the magnetic force generated by the coil ensures precise valve switching. This balance allows the valve to operate reliably and return to its safe default position whenever power is removed.
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Diaphragm Return Spring (D)
The diaphragm return spring is used primarily in diaphragm-type or pilot-operated solenoid valves. It connects the diaphragm to the plunger assembly and helps restore the diaphragm to its original position after the valve closes. This spring ensures that the diaphragm maintains proper tension and sealing performance during operation.
In pilot-operated valves, the diaphragm controls the main fluid passage while the solenoid controls a smaller pilot port. The diaphragm return spring helps stabilize the movement of the diaphragm so that the valve can close quickly and maintain consistent pressure control. Without this spring, the diaphragm might respond slowly or fail to reseal properly, which could cause leakage or unstable valve operation.
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Valve Cover and Body (E)
The valve body is the main structural and pressure-bearing component of the solenoid valve. It houses the inlet and outlet ports, the internal flow passages, the diaphragm, and other sealing components. The valve body is responsible for directing fluid through the valve and maintaining pressure integrity within the system.
The valve cover, located above the body, protects the internal mechanical components from environmental exposure and mechanical damage. Together, the valve cover and body form the main enclosure of the valve assembly.
Valve bodies are manufactured from different materials depending on the application and fluid type. Brass is commonly used for water and air systems, stainless steel is preferred for corrosive or sanitary environments, and engineering plastics may be used for lightweight or chemical-resistant applications.
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Solenoid Tube (F)
The solenoid tube, also known as the core tube or armature tube, is a hollow cylindrical component that houses and guides the plunger during operation. It provides a smooth path for the plunger’s vertical movement when the magnetic field pulls it toward the coil.
This tube also plays an important protective role by separating the electrical components of the solenoid from the process fluid inside the valve body. In most designs, the solenoid tube is made from non-magnetic materials as these prevent interference with the magnetic field and allow the plunger to respond more efficiently to the coil’s electromagnetic force.
Proper alignment and cleanliness of the solenoid tube are essential for reliable valve operation. If debris, corrosion, or surface damage occurs inside the tube, the plunger may stick or move unevenly, which can cause overheating or valve failure.
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Shading Ring (G)
The shading ring is a small loop or ring made from conductive materials such as copper or aluminum. It is installed within the magnetic assembly of AC-operated solenoid valves. Its purpose is to stabilize the magnetic field produced by alternating current.
In AC systems, the magnetic field generated by the coil periodically drops to zero during each electrical cycle. Without additional stabilization, this could cause the plunger to vibrate or chatter.
The shading ring solves this problem by creating a secondary magnetic field with a slight phase delay. This delayed magnetic flux maintains a small magnetic force even when the main magnetic field temporarily collapses.
By smoothing the magnetic force, the shading ring significantly reduces vibration, noise, and mechanical wear. This improves the overall stability and lifespan.
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Seal (H)
The seal is the component responsible for closing the valve seat and preventing fluid leakage. It is typically mounted on the plunger or valve seat and forms a tight sealing surface against the orifice when the valve is closed.
When the coil energizes and the plunger moves, the seal lifts away from the valve seat, allowing fluid to flow through the orifice. When the valve de-energizes, the spring pushes the plunger back into place, pressing the seal firmly against the seat to block the flow.
Seals are usually made from elastomeric or polymer materials that provide both flexibility and chemical resistance. Common sealing materials include NBR (nitrile rubber), EPDM, FKM (Viton), and PTFE. The correct seal material must be selected based on factors such as fluid type, temperature, and chemical compatibility to ensure long service life and reliable sealing performance.
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Diaphragm and Pilot Hole (I)
The diaphragm is a flexible membrane used in many pilot-operated solenoid valves. It acts as a pressure-sensitive barrier that separates the upper control chamber from the main fluid flow passage. The diaphragm works together with the pilot hole, which is a small pressure-balancing opening that helps regulate the pressure above and below the diaphragm.
When the solenoid activates, the plunger opens the pilot hole, allowing pressure in the control chamber to drop. This pressure difference allows the diaphragm to lift upward, opening the main valve passage and allowing fluid to flow. When the solenoid de-energizes, the pilot hole closes, pressure equalizes, and the diaphragm returns to its sealing position.
This design allows a relatively small electromagnetic force to control a much larger flow capacity. As a result, pilot-operated solenoid valves can handle higher flow rates while consuming less electrical power compared with direct-acting valves.
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Orifice (J)
The orifice is the opening that connects the inlet port and outlet port within the valve body. It is the primary passage through which fluid flows when the valve is open. The plunger, seal, or diaphragm moves to either block or expose this opening, thereby controlling the fluid flow. The orifice’s size and shape are critical factors that affect the valve’s flow capacity, pressure drop, and how quickly it responds during operation.
Depending on the valve design, there may be one or multiple orifices. In direct-acting valves, the plunger directly opens or closes the orifice. In pilot-operated valves, the orifice works together with the diaphragm and pilot system to regulate the main flow passage.
QUEEN Solenoid Valves: Built for Reliable Fluid Control
Understanding the key parts of a solenoid valve helps explain how these devices achieve precise and reliable fluid control. Choosing the right valve, however, is just as important as understanding its internal structure.
At KUHNWAY, we provide high-quality solenoid valves designed for stable performance in a wide range of applications. Our lineup includes
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MD Series direct-acting diaphragm solenoid valves for air, water, and light oil systems
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MT Series pilot-operated piston solenoid valves for high-temperature and high-pressure environments such as steam systems.
Contact us today to find the right solenoid valve for your application and improve your system efficiency.
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What are the Parts of Solenoid Valves: Full Guide
Explore key solenoid valve parts, including the coil, spring, body, shading ring, and orifice, and learn how each supports the working of a solenoid valve.