![Solonoid valves](https://upload.wikimedia.org/wikipedia/commons/7/72/Solonoid_valves.jpg)
A solenoid valve is an
electromechanical
In engineering, electromechanics combines processes and procedures drawn from electrical engineering and mechanical engineering. Electromechanics focuses on the interaction of electrical and mechanical systems as a whole and how the two systems ...
ly operated
valve
A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fittings ...
.
Solenoid valves differ in the characteristics of the
electric current
An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The moving pa ...
they use, the strength of the
magnetic field
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
they generate, the mechanism they use to regulate the
fluid
In physics, a fluid is a liquid, gas, or other material that continuously deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear ...
, and the type and characteristics of fluid they control. The mechanism varies from
linear action, plunger-type
actuator
An actuator is a component of a machine that is responsible for moving and controlling a mechanism or system, for example by opening a valve. In simple terms, it is a "mover".
An actuator requires a control device (controlled by control signal) a ...
s to pivoted-armature actuators and rocker actuators. The valve can use a two-port design to regulate a flow or use a three or more port design to switch flows between ports. Multiple
solenoid
upright=1.20, An illustration of a solenoid
upright=1.20, Magnetic field created by a seven-loop solenoid (cross-sectional view) described using field lines
A solenoid () is a type of electromagnet formed by a helix, helical coil of wire whose ...
valves can be placed together on a
manifold
In mathematics, a manifold is a topological space that locally resembles Euclidean space near each point. More precisely, an n-dimensional manifold, or ''n-manifold'' for short, is a topological space with the property that each point has a n ...
.
Solenoid valves are the most frequently used control elements in
fluidics
Fluidics, or fluidic logic, is the use of a fluid to perform analog or digital operations similar to those performed with electronics.
The physical basis of fluidics is pneumatics and hydraulics, based on the theoretical foundation of fluid dyna ...
. Their tasks are to shut off, release, dose, distribute or mix fluids. They are found in many application areas. Solenoids offer fast and safe switching, high-reliability, long service life, good medium compatibility of the materials used, low control power and compact design.
Operation
There are many valve design variations. Ordinary valves can have many ports and fluid paths. A 2-way valve, for example, has 2 ports; if the valve is open, then the two ports are connected and fluid may flow between the ports; if the valve is closed, then ports are isolated. If the valve is open when the solenoid is not energized, then the valve is termed normally open (N.O.). Similarly, if the valve is closed when the solenoid is not energized, then the valve is termed normally closed (N.C.).
There are also 3-way and more complicated designs.
A 3-way valve has 3 ports; it connects one port to either of the two other ports (typically a supply port and an exhaust port).
![Pneumatic Rack and Pinion Actuators](https://upload.wikimedia.org/wikipedia/commons/0/04/Pneumatic_Rack_and_Pinion_Actuators.JPG)
Solenoid valves are also characterized by how they operate. A small solenoid can generate a limited force. An approximate relationship between the required solenoid force ''F
s'', the fluid pressure ''P'', and the orifice area ''A'' for a direct acting solenoid valve is:
:
Where ''d'' is the orifice diameter. A typical solenoid force might be . An application might be a low pressure (e.g., ) gas with a small orifice diameter (e.g., for an orifice area of and approximate force of ).
If the force required is low enough, the
solenoid
upright=1.20, An illustration of a solenoid
upright=1.20, Magnetic field created by a seven-loop solenoid (cross-sectional view) described using field lines
A solenoid () is a type of electromagnet formed by a helix, helical coil of wire whose ...
is able to directly actuate the main valve. These are simply called Direct-Acting solenoid valves. When electricity is supplied, electrical energy is converted to mechanical energy, physically moving a barrier to either obstruct flow (if it is N.O.) or allow flow (if it is N.C.). A spring is often used to return the valve to its resting position once power is shut off. Direct-acting valves are useful for their simplicity, although they do require a large amount of power relative to other types of solenoid valves.
If fluid pressures are high and orifice diameter is large, a solenoid may not generate enough force on its own to actuate the valve. To solve this, a Pilot-Operated solenoid valve design can be used.
Such a design uses the pressurized fluid itself to apply the forces required to actuate the valve, with the solenoid as a "pilot" directing the fluid (see subsection below). These valves are used in dishwashers, irrigation systems, and other applications where large pressures and/or volumes are desired. Pilot-operated solenoids tend to consume less energy than direct-action, although they will not work at all without sufficient fluid pressure and are more susceptible to getting clogged if the fluid has solid impurities.
A direct-acting solenoid valve typically operates in 5 to 10 milliseconds. Pilot-operated valves are slightly slower; depending on their size, typical values range from 15 to 150 milliseconds.
Power consumption and supply requirements of the solenoid vary with application, being primarily determined by fluid pressure and orifice diameter. For example, a popular -inch 150 psi sprinkler valve, intended for 24 VAC (50–60 Hz) residential systems, has a momentary inrush of 7.2 VA, and a holding power requirement of 4.6 VA. Comparatively, an industrial -inch 10,000 psi valve, intended for 12, 24, or 120 VAC systems in high-pressure fluid and cryogenic applications, has an inrush of 300 VA and a holding power of 22 VA. Neither valve lists a minimum pressure required to remain closed in the unpowered state.
Pilot-operated
While there are multiple design variants, the following is a detailed breakdown of a typical pilot-operated solenoid valve. They may use metal seals or rubber seals, and may also have electrical interfaces to allow for easy control.
The diagram to the right shows the design of a basic valve, controlling the flow of water in this example. The top half shows the valve in its closed state. An inlet stream of pressurized water enters at A. B is an elastic diaphragm and above it is a spring pushing it down. The diaphragm has a pinhole through its center which allows a very small amount of water to flow through. This water fills cavity C so that pressure is roughly equal on both sides of the diaphragm. However, the pressurized water in cavity C acts across a much greater area of the diaphragm than the water in inlet A. From the equation
, the force from cavity C pushing downward is greater than the force from inlet A pushing upward, and the diaphragm remains closed.
Diaphragm B will stay closed as long as small drain passage D remains blocked by a pin, which is controlled by solenoid E. In a normally closed valve, supplying an electric current to the solenoid will raise the pin via magnetic force, and the water in cavity C drains out through passage D faster than the pinhole can refill it. Less water in cavity C means the pressure on that side of the diaphragm drops, proportionately dropping the force too. With the downward force of cavity C now less than the upward force of inlet A, the diaphragm is pushed upward, thus opening the valve. Water now flows freely from A to F. When the solenoid is deactivated and passage D is closed, water once again accumulates in cavity C, closing the diaphragm once the downward force exerted is great enough.
This process is the opposite for a normally open pilot-operated valve. In that case, the pin is naturally held open by a spring, passage D is open, and cavity C is never able to fill up enough, pushing open diaphragm B and allowing unobstructed flow. Supplying an electric current to the solenoid pushes the pin into a closed position, blocking passage D, allowing water to accumulate in cavity C, and ultimately closing diaphragm B.
In this way, a pilot-operated solenoid valve can be conceptualized as two valves working together: a direct-acting solenoid valve which functions as the "brain" to direct the "muscle" of a much more powerful main valve which gets actuated
pneumatically
Pneumatics (from Greek ‘wind, breath’) is a branch of engineering that makes use of gas or pressurized air.
Pneumatic systems used in industry are commonly powered by compressed air or compressed inert gases. A centrally located and e ...
or
hydraulically
Hydraulics (from Greek language, Greek: Υδραυλική) is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is th ...
. This is why pilot-operated valves will not work without a sufficient pressure differential between input and output, the "muscle" needs to be strong enough to push back against the diaphragm and open it. Should the pressure at the output rise above that of the input, the valve would open regardless of the state of the solenoid and pilot valve.
Components
![Solenoid valve core tube produced by deep drawing](https://upload.wikimedia.org/wikipedia/commons/9/92/Solenoid_valve_core_tube_produced_by_deep_drawing.jpg)
Solenoid valve designs have many variations and challenges.
Common components of a solenoid valve:
*Solenoid subassembly
**Retaining clip (a.k.a. coil clip)
**Solenoid coil (with magnetic return path)
**Core tube (a.k.a. armature tube, plunger tube, solenoid valve tube, sleeve, guide assembly)
**Plugnut (a.k.a. fixed core)
**Shading coil (a.k.a. shading ring)
**Core spring (a.k.a. counter spring)
**Core (a.k.a. plunger, armature)
*Core tube–bonnet seal
*Bonnet (a.k.a. cover)
*Bonnet–diaphragm–body seal
*Hanger spring
*Backup washer
*Diaphragm
**Bleed hole
*Disk
*Valve body
**Seat
The core or plunger is the magnetic component that moves when the solenoid is energized. The core is coaxial with the solenoid. The core's movement will make or break the seals that control the movement of the fluid. When the coil is not energized, springs will hold the core in its normal position.
The plugnut is also coaxial.
The core tube contains and guides the core. It also retains the plugnut and may seal the fluid. To optimize the movement of the core, the core tube needs to be nonmagnetic. If the core tube were magnetic, then it would offer a shunt path for the field lines. In some designs, the core tube is an enclosed metal shell produced by
deep drawing
Deep drawing is a sheet metal metal forming, forming process in which a sheet metal blank is radially drawn into a forming die by the mechanical action of a punch. It is thus a shape transformation process with material retention. The process is c ...
. Such a design simplifies the sealing problems because the fluid cannot escape from the enclosure, but the design also increases the magnetic path resistance because the magnetic path must traverse the thickness of the core tube twice: once near the plugnut and once near the core. In some other designs, the core tube is not closed but rather an open tube that slips over one end of the plugnut. To retain the plugnut, the tube might be crimped to the plugnut. An O-ring seal between the tube and the plugnut will prevent the fluid from escaping.
The solenoid coil consists of many turns of copper wire that surround the core tube and induce the movement of the core. The coil is often encapsulated in epoxy. The coil also has an iron frame that provides a low magnetic path resistance.
Materials
The valve body must be compatible with the fluid; common materials are brass, stainless steel, aluminum, and plastic.
The seals must be compatible with the fluid.
To simplify the sealing issues, the plugnut, core, springs, shading ring, and other components are often exposed to the fluid, so they must be compatible as well. The requirements present some special problems. The core tube needs to be non-magnetic to pass the solenoid's field through to the plugnut and the core. The plugnut and core need a material with good magnetic properties such as iron, but iron is prone to corrosion.
Stainless steel
Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's corros ...
s can be used because they come in both magnetic and non-magnetic varieties. For example, a solenoid valve might use 304 stainless steel for the body, 305 stainless steel for the core tube, 302 stainless steel for the springs, and 430 F stainless steel (a magnetic stainless steel) for the core and plugnut.
Types
Many variations are possible on the basic, one-way, one-solenoid valve described above:
* one- or two-solenoid valves;
*
direct current
Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or even ...
or
alternating current
Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in whic ...
powered;
* different number of ways and positions;
Common uses
Solenoid valves are used in
fluid power
Fluid power is the use of fluids under pressure to generate, control, and transmit power. Fluid power is subdivided into hydraulics using a liquid such as mineral oil or water, and pneumatics using a gas such as air or other gases. Compressed- ...
pneumatic and hydraulic systems, to control cylinders, fluid power motors or larger industrial valves. Automatic
irrigation sprinkler
An irrigation sprinkler (also known as a water sprinkler or simply a sprinkler) is a device used to irrigate (water) agricultural crops, lawns, landscapes, golf courses, and other areas. They are also used for cooling and for the control of airbo ...
systems also use solenoid valves with an automatic
controller
Controller may refer to:
Occupations
* Controller or financial controller, or in government accounting comptroller, a senior accounting position
* Controller, someone who performs agent handling in espionage
* Air traffic controller, a person ...
. Domestic
washing machine
A washing machine (laundry machine, clothes washer, washer, or simply wash) is a home appliance used to wash laundry. The term is mostly applied to machines that use water as opposed to dry cleaning (which uses alternative cleaning fluids and ...
s and
dishwasher
A dishwasher is a machine that is used to clean dishware, cookware, and cutlery automatically. Unlike manual dishwashing, which relies heavily on physical scrubbing to remove soiling, the mechanical dishwasher cleans by spraying hot water, ...
s use solenoid valves to control water entry into the machine. They are also often used in paintball gun triggers to actuate the hammer valve. Solenoid valves are usually referred to simply as "solenoids."
Solenoid valves can be used for a wide array of industrial applications, including general on-off control, calibration and test stands, pilot plant control loops, process control systems, and various original equipment manufacturer applications.
History and commercial development
In 1910,
ASCO Numatics
Emerson Electric Co. is an American multinational corporation headquartered in Ferguson, Missouri. The Fortune 500, ''Fortune'' 500 company manufactures products and provides engineering services for industrial, commercial, and consumer marke ...
became the first company to develop and manufacture the solenoid valve.
See also
*
Air-operated valve
An air-operated valve, also known as a pneumatic valve, is a type of power-operated pipe valve that uses air pressure to perform a function similar to a solenoid. As air pressure is increased, the compressed air starts to push against the piston o ...
References
External links
Solenoid Valve Types circuit functions and operation types of solenoid valves explained with illustrations
{{DEFAULTSORT:Solenoid Valve
Valves
History of technology
Mechanisms (engineering)
Automobile transmissions
Continuously variable transmissions