Solenoid valve
A solenoid valve is an electromechanical valve for use with liquid or gas controlled by running or stopping an electrical current through a solenoid, which is a coil of wire, thus changing the state of the valve. The operation of a solenoid valve is similar to that of a light switch, but typically controls the flow of air or water, whereas a light switch typically controls the flow of electricity. Solenoid valves may have two or more ports: in the case of a two-port valve the flow is switched on or off; in the case of a three-port valve, the outflow is switched between the two outlet ports.
Solenoid valves may use metal seals or rubber seals, and may also have electrical interfaces to allow for easy control. Multiple solenoid valves can be placed together on a manifold
A spring may be used to hold the valve opened or closed while the valve is not activated.
A common use for 2 way solenoid valves is in central heating. The solenoid valves are controlled by an electrical signal from the thermostat to regulate the flow of heated water from a heat pump to the in room radiators. Such valves are particularly useful when multiple heating zones are driven by a single heat pump. Commercially available solenoid valves for this purpose are often referred to as Zone valves.
A common use for 3-way solenoid valves are as pilot valves for other pneumatically operated type of valves, such as angle seat valves, ball valves, diaphragm valves etc. An electrical current, e.g. from an automation system, activates the pilot valve which in turn alters the position of the process valve. When the action is reversed, the air is exhausted through the third port of the pilot solenoid valve. A solenoid is a device which converts energy into linear motion. This energy may come from an electromagnetic field, a pneumatic (air-powered) chamber or a hydraulic (fluid-filled) cylinder. Solenoids are commonly found in electric bell assemblies, automotive starter systems, industrial air hammers and many other devices which rely on a sudden burst of power to move a specific part.
In order to understand the underlying principle of a solenoid, let’s examine a typical pinball machine. At the beginning of play, a steel ball rests on a rubber-tipped plunger. The plunger is held in place by a compression spring, which means it has no energy to move the ball when at rest. The player’s hand provides additional energy as the plunger assembly is pulled back. Upon release the compression spring forces almost all of the plunger pin’s kinetic energy on a small area of the steel ball. The ball is flung into the playing field and the pinball game begins. This manual plunger is a rudimentary example of a solenoid.
The difficulty with using manual pinball plungers on other machines is that someone must constantly pull the spring back and release the energy by hand. An improved solenoid would provide its own means of pulling back on the pin and releasing it under control. This is the principle behind a simple electric solenoid. A metallic cylinder acts as the ‘plunger’. A compression spring holds this metal pin partially out of an electromagnetic housing. When power from a battery or electric generator flows around the electromagnet, the metal pin or cylinder is magnetically drawn inside the housing, much like the player’s hand pulls the plunger back in our pinball example. When the electric current stops, the pin is released and the compression spring sends it forward with significant force. The pin may strike the inside of a bell or forcefully eject a part from a molding machine. Many electronic machines contain numerous solenoids- the pinball machine depends heavily on solenoids triggered by the ball’s contact with electrical circuits.
Other types of solenoids depend on compressed air for their power. A single piston may be placed in an airtight cylinder connected to a source of highly-compressed air. A strong internal spring may hold the piston in place until the air pressure has reached a predetermined level and then the piston is released. The compressed air is allowed to escape as the piston drives forward. Because the energy released by a solenoid can be concentrated, pneumatic solenoids are popular for heavy tools and machining applications which require substantial power. A jackhammer is a good example of a pneumatic solenoid in action. The central piston is driven by air into the concrete, then the recoil of the hammer returns the piston to its original position.
An even more powerful solenoid uses hydraulics as its source of power. The piston or pin is seated in a cylinder filled with a hydraulic fluid. As this hydraulic fluid fills the cylinder everything is pushed forward, including the piston or pin. As the piston travels towards a piece of metal or other target, the fluid buildup becomes very resistant to compression. The piston or pin will concentrate all of the cylinder’s energy on whatever it encounters, even the heaviest titanium. When the solenoid has released all of its energy, the hydraulic fluid drains out of the chamber and the piston is drawn back to its original position. This action can take place in a matter of seconds. Hydraulic solenoids are so powerful that they are generally used only for the heaviest projects. Wave pools use hydraulic solenoids to release the giant stoppers at the bottom of their holding tanks. Aircraft manufacturers use hydraulic solenoids to bend titanium and other heavy metals.
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May 25th, 2007 at 3:43 pm
In many process plants, a shut-off valve in a safety loop is the preferred device that enables operators to shut down process lines in the event of an emergency, referred to as ESD
Such emergency shutdown (ESD) shut-off valves are usually activated by a solenoid valve and are also equipped with limit switches for position feedback. Not surprisingly in ‘normal’ production situations, ESD shut-off valves remain unused, typically fixed in one position for many months or even many years.
Special test procedures have been developed and are used in most production environments which offer an effective and practical method for testing shut-off valves to ensure they will work when needed.
For example, partial stroke testing is a common practice, allowing valves to be partially stroked for testing purposes, without causing major interruption or down-time to the production process.
As part of their on-going development of a wide range of control valves, positioners and accessories, Samson Controls offers a range of electro-pneumatic positioners.
Further reading
Building automation system with Ethernet
The Trovis Modulon Automation System can easily be integrated into existing corporate networks thanks to its Ethernet interface and the use of the standard TCP/IP protocol
Temperature controller with electric actuator
The Samson temperature control designed for application in instantaneous water heating systems helps to achieve hot water at a constant temperature straight out of any tap in a building
These include their Type 3730-3 model which has been enhanced and incorporates an ESD function to enable partial stroke tests to be carried out, without disrupting the process line.
The positioner can be mounted on the valve in addition to the solenoid valve, or to replace it, and enables the valve to be moved precisely to follow the set point within the valve working range.
The partial stroke test is completely integrated into the positioner to detect a sticking valve, caused for example, by corrosion.
Test schedules are flexible and can be prolonged if necessary to suit specific application requirements, while test validation can be performed simply by using the corresponding instrumentation and initiating it over a commonly available SIS logic solver.
May 25th, 2007 at 3:45 pm
Continuing to lead the industry in creativity and technology, Hydracon also announces its new model ocean submersible Miniature Solenoid Valve 1719-100.
These new solenoid valves provide significant weight and space advantages for use on new generation lightweight and compact subsea control systems. Specifically designed for Oil & Gas Deepwater Drilling, Production, and Intervention Systems. The Company is looking forward to new ventures in Subsea Processing.
The solenoid valves are specifically created for harsh environment applications. The sealed construction of the solenoids conforms to IP68 of IEC529 standards for continuous immersion in water in ambient pressures to 4,500 psi (10,000 ft ocean depth). In addition, the solenoid valves are corrosion resistant in seawater, internally and externally.
The new Model 1719-100 environmentally sealed Solenoid Valve is a latching model, for an operating pressure of 3,000 psi differential, and having a flow capacity of 0.1 inch ESEOD. The solenoids are rated at 3.0 amp @ 24vdc and are provided with underwater connectors. Major advantages of this miniature series are its small size, low weight (only about 3.5 lbs), and low power.
July 29th, 2007 at 5:42 am
Any wireles control valve… hahaha without any instrument air or … hemm
September 10th, 2007 at 11:27 pm
A solenoid valve has two main parts: the solenoid and the valve. The solenoid converts electrical energy into mechanical energy which, in turn, opens or closes the valve mechanically. An excellent source of information on the different types of solenoid valve and how they work can be found at http://www.mmint.co.uk1 .
Solenoid valves may use metal seals or rubber seals, and may also have electrical interfaces to allow for easy control. A spring may be used to hold the valve opened or closed while the valve is not activated.
A- Input side B- Diaphragm C- Pressure chamber D- Pressure relief conduit E- Solenoid F- Output side
A- Input side
B- Diaphragm
C- Pressure chamber
D- Pressure relief conduit
E- Solenoid
F- Output side
In some solenoid valves the solenoid provides the full power for the operation of the main valve while there is a certain type where the solenoid, using very little power, controls a secondary pilot valve and it is the pressure of the fluid itself which provides the power for the actuation of the main valve. These types of valves are commonly used in washing machines, gardening and similar uses.
The diagram to the right shows the design of one such valve. If we look at the top figure we can see the valve in its closed state. The water under pressure enters at A. B is an elastic diaphragm and above it is a weak spring pushing it down. The function of this spring is irrelevant for now as the valve would stay closed even without it. The diaphragm has a pinhole through its center which allows a very small amount of water to flow through it. This water fills the cavity C on the other side of the diaphragm so that pressure is equal on both sides of the diaphragm. While the pressure is the same on both sides of the diaphragm, the force is greater on the upper side which forces the valve shut against the incoming pressure. By looking at the figure we can see the surface being acted upon is greater on the upper side which results in greater force. On the upper side the pressure is acting on the entire surface of the diaphragm while on the lower side it is only acting on the incoming pipe. This results in the valve being securely shut to any flow and, the greater the input pressure, the greater the shutting force will be.
Now let us turn our attention to the small conduit D. Until now it was blocked by a pin which is the armature of the solenoid E and which is pushed down by a spring. If we now activate the solenoid, the water in chamber C will flow through this conduit D to the output side of the valve. The pressure in chamber C will drop and the incoming pressure will lift the diaphragm thus opening the main valve. Water now flows directly from A to F.
When the solenoid is again deactivated and the conduit D is closed again, the spring needs very little force to push the diaphragm down again and the main valve closes. In practice there is often no separate spring, the elastomer diaphragm is moulded so that it functions as its own spring, preferring to be in the closed shape.
From this explanation it can be seen that this type of valve relies on a differential of pressure between input and output as the pressure at the input must always be greater than the pressure at the output for it to work. Should the pressure at the output, for any reason, rise above that of the input then the valve would open regardless of the state of the solenoid and pilot valve.
A common use for 2 way solenoid valves is in central heating. The solenoid valves are controlled by an electrical signal from the thermostat to regulate the flow of heated water to the heating elements within the occupied space. Such valves are particularly useful when multiple heating zones are fed by a single heat source. Commercially available solenoid valves for this purpose are often referred to as Zone valves.