Solenoid valve
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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.ja:電磁弁 nn:Magnetventil
