This article will take an in-depth look at 3-Way solenoid valves.
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A solenoid valve is an electro-mechanical valve for the control of the flow of liquid or gas. There are many solenoid valves, but the two most common are direct-acting (or direct-driven) and pilot-driven (or pilot-controlled). The primary orifice in the valve body is opened and closed by pilot-controlled valves. Pilot-driven valves are the most popular type of solenoid valves. While direct-driven solenoid valves are the only flow path in the valve, they directly open or close the primary valve orifice. Direct-driven solenoid valves are utilized in applications or systems that call for modest flow rates or low-pressure differentials across the valve orifice. There are various kinds of solenoid valves. This article focuses on 3-way solenoid valves.
A 3-way solenoid valve features three ports: an orifice, a cavity, and a stop port, which are used for directional control. The term "3-way" (or "3-port") solenoid valve describes a valve with three ports, making it ideal for switching the direction of flow. There are three functional types of 3-way valves: normally-closed (NC), normally-open (NO), and universal. Normally-closed valves block the path between the intake and outlet ports until the coil is energized. Normally-open valves allow fluid to flow from the intake to the outlet while blocking the exhaust port when the coil is de-energized. Universal valves can handle flow in any direction and can be configured as either NC or NO, making them versatile for choosing or diverting flow.
The 3-way solenoid valve features two distinct orifices: the stop orifice and the body orifice, with the latter remaining constantly open. This configuration allows for two separate flow paths. When the valve is activated, the plunger moves either up or down. Raising the plunger seals the stop orifice while opening the body orifice, thus enabling flow through the valve’s body. Conversely, when the plunger is lowered, it seals off the body orifice, opens the stop orifice, and redirects the flow through the stop port.
Gas or liquid flow in a pipe can be closed, opened, dosed, distributed, or mixed using 3-way solenoid valves. A solenoid valve's circuit function communicates the precise purpose of the device. These solenoid valves use different operating principles most suited for an application. All solenoid valves, however, operate according to the same fundamental principle. A 3-way solenoid valve is operated electrically. The valve has a solenoid, an electric coil with a rotating ferromagnetic core (plunger) in the middle. The plunger seals off a tiny opening when it is resting. The coil produces a magnetic flux when an electric current flows through it.
The magnetic field generated by the coil moves the plunger, thereby opening the orifice. This is the basic principle behind the operation of solenoid valves. The key components of a solenoid valve are the solenoid and the valve body. The solenoid features an iron core (plunger) encircled by an electromagnetically inductive coil, which is housed in a casing, typically made of iron or steel, to focus the magnetic field produced by the coil.
A 3-way solenoid valve can be either normally-open (NO) or normally-closed (NC) when not energized. In a normally-closed valve, the orifice remains closed, while a normally-open valve has the orifice open when de-energized. The coil is composed of multiple turns of tightly-wound copper wire, through which an electrical current flows to create a strong magnetic field. When current flows through the coil, it generates a magnetic flux that overcomes a small spring attached to one end of the plunger, causing the plunger to move. A solenoid converts electrical energy into mechanical force. For normally-closed valves, lifting the plunger opens the orifice, allowing fluid to pass through. For normally-open valves, lowering the plunger closes the orifice and stops the flow. The shading ring or shading coil prevents AC (alternating current) coils from vibrating and buzzing. It consists of a few turns of an electrical conductor, such as copper or aluminum, and helps in creating a phase-shifted magnetic field to reduce noise, prevent mechanical damage, and protect power contacts.
Solenoid valves can be constructed from various materials, including bronze, aluminum, steel, and plastic. The chemical properties of these materials affect their resistance to corrosion, making material compatibility with the medium a key factor in selecting a solenoid valve. The choice of material for the valve housing should be based on the chemical composition and temperature of the media being controlled.
Plastic is known for its ability to handle a wide range of media but may not perform well with excessively hot fluids. For high-temperature applications, metal solenoid valves are generally preferred. Additionally, the valve material must be compatible with the fluid’s acidic or alkaline properties. For fluids intended for human consumption, stainless steel valves are highly recommended due to their suitability for such applications.
Three-way solenoid valves come in various types, each with distinct operating principles: direct, semi-direct, and indirect (or pilot-acting). It is important to determine whether a direct, indirect, or semi-direct valve is needed for a specific application. Direct-operated valves are ideal for simple on/off control with minimal closing force requirements. Pilot-operated valves are best suited for large flow lines and applications where strong closing forces are necessary. If the valve is intended to remain open most of the time, a normally open solenoid valve is generally the most appropriate choice.
Solenoid coils are available in various voltages for both direct current (DC) and alternating current (AC). The choice of a 3-way solenoid valve depends on safety considerations and the power requirements of the application. DC valves, particularly those with lower voltages, are generally safer compared to AC valves, but they tend to be less powerful. For most applications, simple 12V DC solenoid valves are sufficient unless significant closing forces are needed.
Depending on the application, a solenoid valve may be subjected to either harsh or mild environmental conditions. For example, irrigation solenoid valves used in agricultural settings must be made from climate-resistant materials to withstand harsh external elements. In contrast, in environments where external conditions are less severe, a solenoid valve made of durable materials like metal may be appropriate. Additionally, for environments prone to explosions, an explosion-proof valve is necessary, while a dust-proof valve is required for dusty conditions.
The response time of a valve is the duration required to transition from the open to the closed position, or vice versa. Response times can vary between solenoid valves and are influenced by factors such as the valve's design, the characteristics of the coil, air pressure, and the viscosity of the medium. DC valves generally have slightly slower response times compared to AC valves. Typically, direct-operated valves respond faster than indirect ones. However, fast response valves are not ideal for all applications, particularly where water hammer is a concern—this is a phenomenon where a sudden change in fluid flow creates a pressure surge in the piping system, potentially damaging the system and its pipes.
Choosing a 3-way solenoid valve depends on the operating pressure of the system. Exceeding the valve's specified maximum pressure can lead to bursting or damage, potentially creating unsafe conditions. Therefore, it is essential to select a valve that can withstand the maximum pressure required for the application. Additionally, different fluids have varying pressure requirements, so it is important to consider both the system pressure and the type of medium when determining the appropriate valve pressure ratings.
It is crucial to ensure that the valve materials can handle both the minimum and maximum temperatures required by the application. Temperature affects the fluid's viscosity and flow, which in turn impacts the valve's performance. Exceeding the specified temperature limits is not recommended, as high temperatures can damage the valve’s coil and other components.
The IP rating, or “Ingress Protection” code, indicates the level of protection a solenoid valve provides against the ingress of water, dust, and contact with hazardous parts. This globally recognized standard is typically expressed with two digits. The first digit denotes the degree of protection against solid objects and access to potentially dangerous components, while the second digit indicates the level of moisture protection.
Threading is essential for installing and securely fastening the valve to the piping system. It is important to select the correct threading and valve size for the system. The valve size must be compatible with the system's flow capacity and should not only meet normal flow requirements but also accommodate emergency situations. However, an excessively large valve capacity can be wasteful and unnecessary.
Stroke refers to the distance a plunger travels before stopping. Typically, the solenoid's initial force is related to the stroke length: a longer stroke generally results in less force. Therefore, understanding the relationship between force and stroke is crucial before using any solenoid.
Ethylene propylene diene monomer (EPDM) rubber, nitrile butadiene rubber (NBR), and fluoroelastomer are three types of seal or diaphragm materials that can be used depending on the chemical properties and temperature of the media. However, seals can obstruct the flow of media and may pose risks, particularly if the media is intended for consumption.
The choice between a normally open or normally closed valve depends on the operational requirements. A normally closed valve is generally preferred if the valve needs to open quickly or remain closed for longer periods, while a normally open valve is suitable for situations requiring longer opening times or quicker closure.
The solenoid assembly is attached to this section of the valve. The circuit carrying the fluid to be controlled connects to the valve body. The body also includes three ports that link to the solenoid valve. It is essential for the valve body to handle the fluid without damage, which is why manufacturers typically use high-quality materials for this component.
The solenoid valve coil is made of wire wound around a magnetic core. This coil acts as the actuator assembly for the solenoid valve, creating the movement needed to shift a disc or seal and control the flow of media through the 3-way solenoid valve. Factors such as the coil's size affect the valve's strength and closing power.
The plunger is the moving part of a three-way solenoid valve that opens or closes the valve. Typically made of ferromagnetic material, the cylindrical plunger moves up or down when the solenoid coil is energized, creating a magnetic field. The plunger's movement controls the flow of media through the valve based on the desired action and valve mechanism. It can allow fluid to pass, block it, or regulate the flow. The plunger houses a seal, often made of rubber or metal, with rubber being the most common.
The inlet port is where the media enters the solenoid valve. This opening allows fluid to enter the valve before interacting with the seal or disc that controls the flow. Depending on its function, a 3-way solenoid valve may have one or more inlet ports.
The outlet port provides an exit for the controlled fluid. It is where the media exits the valve after being partially or fully allowed through. Similar to the inlet port, a 3-way solenoid valve may have multiple outlet ports depending on its design.
The third port in a three-way solenoid valve is often called the stop port due to its role in regulating the flow of gas or liquid. It may also serve as a safety valve to connect to the external environment in situations of pressure increases, such as in a boiler.
The solenoid coil functions as a switch in 3-way solenoid valves. It acts like a magnet, drawing the solenoid’s body when current flows through it.
The solenoid spring provides the necessary tension to hold the plunger in place. After the coil's current stops, residual magnetism may cause the plunger to remain stuck in the up or down position. The spring pulls the plunger back to its original position, preventing the current from continuing to flow and stopping the plunger from moving down due to gravity.
An electric actuator operates the solenoid valve, requiring lead wires for current transmission. These wires connect to the power supply on one end and the valve’s electrical circuitry on the other, ensuring current flows through the solenoid valve to actuate the plunger as needed.
The orifice is the passage between the input and output ports, controlled by the plunger to regulate media flow into and out of the valve. Depending on the valve's function and operating principle, a 3-way solenoid valve may have one or more orifices.
The sealing disc, or gasket, is the component that closes the valve and must be made from high-quality materials to resist corrosion. It should be kept clean to ensure that the valve does not partially close due to debris.
The diaphragm, used in pilot-operated solenoid valves, utilizes pressure differences to close the main orifice. It is a moving component that must be kept clean to ensure proper valve function.
The armature tube guides the plunger and must be free of defects to prevent jamming due to tight clearances. Dirt can also affect the plunger's movement, potentially causing heat and damage to the valve.
The material chosen for the valve body should be compatible with the fluid. Solenoid valve bodies are typically made from stainless steel, aluminum, brass, or plastic. Seals must also match the fluid type. Components like the core, plug nut, and shading ring need to be fluid-compatible for effective sealing. The core tube should be non-magnetic to allow the solenoid’s field to pass through, with materials like iron and stainless steel commonly used due to their magnetic properties and resistance to corrosion.
The manufacturing process for 3-way solenoid valves is intricate. Each major component is produced separately, often following a checklist of spare parts and materials. Below is an overview of the common manufacturing steps for 3-way solenoid valves.
3-way solenoid valves enable design engineers to switch or divert flows or to discharge unnecessary flows, expanding the capabilities of fixed displacement pumps. Actuation can be achieved through electronics, manual methods, solenoid coils, or hydraulic oil, with some systems combining multiple methods to optimize performance.
After selecting the material, it is cut into required sizes. Components are then partially heated to a specific temperature for forging. Excess material or burrs are trimmed, and the body is flashed into the valve shape. Sandblasting smooths and cleans the valve body according to the required specifications.
Following sandblasting, the valves are sorted to remove any defective ones. Machining is used to refine the sizes and shapes of threads and holes based on design and customer needs. Surface treatments with acids may be applied to finalize the valve.
Correct assembly techniques are critical in manufacturing. During assembly, workers connect each valve component, often assembling by hand. The main parts of the valve are cleaned and assembled individually, with the valve body typically used as a reference during the assembly process.
Pressure testing involves checking for leaks under pressure to ensure the valve's functionality. Air at 6 to 8 bars (87 to 116 psi) may be used to test the closed valve for a set period, ranging from two hours to a day, depending on the valve size. The applied pressure must meet or exceed the valve's rated working pressure, and the sealing surface must remain leak-free. Valves that fail this test are repaired; those that pass proceed to the next stage.
Inspection and quality control are the final steps in valve production, where each valve is examined to ensure it meets standards and is free from leaks or defects.
Direct-acting solenoid valves function by using the armature's movement to directly open or close the valve. The design includes a seal disc and a solenoid plunger that quickly operates the orifice.
These 3-way direct-acting solenoid valves are often affordable, featuring a compact coil that reduces power usage and minimizes heat. They are well-suited for controlling actuators and cylinders and do not require a pressure differential to operate. Available in brass, plastic, or stainless steel, these valves are versatile for various general-purpose media applications. Unlike pilot-operated valves, which need pressure to stay closed, direct-acting solenoids rely on the moving core for sealing and remain closed even in the absence of pressure.
3-way semi-direct-acting solenoid valves blend the features of direct-acting and indirect-acting solenoid valves. They are capable of handling relatively high flow rates even at zero pressure (0 psi). Unlike indirect valves, these solenoid valves have a plunger directly connected to a movable membrane or diaphragm with a small aperture and pressure chambers on either side. The strong coils used in 3-way semi-direct-acting solenoid valves do result in a modest increase in energy consumption.
Three-way pilot-acting solenoid valves control flow based on the differential pressure across the valve ports. Also referred to as servo-assisted solenoids, these valves are known for their low power consumption, broad operating pressure ranges, and high flow capacities. They feature a small chamber located directly above the diaphragm, which aids in valve operation. Process fluid enters this chamber through a tiny opening in the entrance port. The normally closed valve maintains its seal by compressing the diaphragm and pressing it against the seat.
When current is applied to the pilot solenoid, the pilot fluid in the chamber is pushed back through the aperture at the inlet port, merging with the main flow through the valve body. This current raises the diaphragm against the spring pressure, enabling the valve to operate effectively.
A three-way normally-open solenoid valve features three pipe connections: the stop port, body cavity port, and body orifice port. It has two orifices—the body orifice and the stop orifice—that remain open at all times, creating two flow pathways. When power is off, the plunger is raised, sealing the stop orifice and allowing flow from the body orifice port through to the cavity port. When power is applied, the plunger descends, closing the body orifice and opening the stop orifice. This action redirects the media flow from the cavity port to the stop port.
A three-way, normally-closed solenoid valve features three pipe connections: the cavity port, the body orifice port, and the stop port. This valve includes two orifices—the body orifice and the stop orifice—that are always open, facilitating two distinct flow paths. Unlike its normally-closed counterpart, this valve operates differently when power is applied. When the valve is not energized, the body orifice is closed while the stop orifice remains open, allowing fluid to flow from the cavity port through the valve and out of the stop port. When the solenoid coil is energized, the plunger moves up, closing the stop orifice and opening the body orifice. This configuration allows flow from the body orifice port through the valve body and out the stop port.
A 3-way directional control solenoid valve has three pipe connections: the cavity port, the body orifice port, and the stop port. It features two orifices: the body orifice and the stop orifice. With one of the orifices always open, the valve can create two distinct flow paths. When the valve is powered on, the plunger either rises or falls. If the plunger rises, it opens the body orifice and closes the stop orifice, allowing flow through the valve body. Conversely, when the plunger falls, it closes the body orifice, opens the stop orifice, and directs flow through the stop port.
Three-port designs are commonly used in 3-way, 2-position solenoid valves, enabling various flow configurations despite connecting only two ports at any given time. This type of valve features several tapered cylinders that decrease in size from top to bottom. It is designed to fit into a port with a machined cavity. The valve includes two main pathways: a supply port, which is pressurized only when the valve is activated, and a tank port that acts as a reservoir for hydraulic fluid. A seal separates these two pathways. The spool inside the valve moves back and forth, directing pressurized hydraulic fluid to either the supply or tank port, depending on the valve’s position. This mechanism allows engineers to switch between two different functions or to direct flow away from where it is not needed, thereby enhancing the versatility of fixed displacement pumps. Actuation can be achieved through various methods, including electronics, manual controls, solenoid coils, or hydraulic oil. Some advanced systems even combine multiple actuation techniques to optimize performance.
A 3-way piloted solenoid valve features a piston that seals the main valve seat. When the valve is closed, pressure accumulates on the piston from a bleed orifice. This pressure differential between the inlet and outlet ports keeps the valve in the closed position. When the pilot valve opens, it releases pressure from the piston, allowing the valve to open. Internal piloted 3-way solenoid valves need only a small pressure differential to operate effectively.
Externally Piloted 3-Way Solenoid Valves: Operation and Function
In an externally piloted 3-way solenoid valve, the valve seat remains closed when the valve is unpressurized. Upon energizing the valve, the piston lifts, causing the valve to open. This type of valve requires an independent pilot medium for actuation, which is connected to the top of the actuator.
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