subject: Locking Solenoids There Every Day Uses [print this page] A solenoid is defined as a coil of wire commonly in the form of a long cylinder that when carrying a current resembles a bar magnet so that a moveable core is drawn into the coil when a current flows. A more simple definition is that a solenoid is a coil and a moveable iron core used to convert electrical energy into mechanical energy. Solenoids have been around for decades but now range in size from less than one-quarter of an inch to more than 15 inches in diameter with force outputs of less than an ounce to a ton.
In engineering the term solenoid may also refer to a variety of transducer devices that convert energy into linear motion. The term is also often used to refer to a solenoid value which is an integrated device containing an electromechanical solenoid which actuates either a pneumatic or hydraulic valve, or a solenoid switch, which is a specific type of relay that internally uses an electromechanical solenoid to operate an electrical switch; for example, an auto mobile starter set up or a linear solenoid, which is an electromechanical solenoid.
Hydraulic solenoid valves
Hydraulic solenoid valves are in general similar to pneumatic solenoid valves except that they control the flow of hydraulic fluid (oil), often at around 3000 psi (210 bar, 21 MPa, 21 MN/m). Hydraulic Machinery uses solenoids to control the flow of oil to rams or actuators to (for instance) bend sheets of titanium in aerospace manufacturing. Solenoid-controlled valves are often used in irrigation systems, where a relatively weak solenoid opens and closes a small pilot valve, which in turn activates the main valve by applying fluid pressure to a piston or diaphragm that is mechanically coupled to the main valve. Solenoids are also in everyday household items such as washing machines to control the flow and amount of water into the drum.
Transmission Solenoids control fluid flow through an automatic transmission and are typically installed in the transmission valve body.
In short: the magnetic Field inside an infinitely long solenoid is homogeneous and its strength does not depend on the distance from the axis, nor on the solenoid cross-sectional area.
Rotary and linear solenoids operate in generally the same fashion. The direction of movement is either rotary or linear based on the mechanical assembly within which the electromagnetic circuit is encased.
Rotary solenoids provide rotational stroke measured in degrees. Some are unidirectional and some are bidirectional. Most have a spring return to bring the armature (moving member) back to the home position. Rotary solenoids are often used when package size is of the utmost importance and the work they perform is distributed more evenly across their stroke. Rotary solenoids have higher starting force/torque than do linear solenoids. They are more resistant to shock. Rotary solenoids also offer far longer life (in number of actuations) than do linear solenoids. One of the most common applications that helps to illustrate a rotary solenoid function is opening and closing a laser shutter.
Linear solenoids provide linear stroke usually less than one inch in either direction. Just like rotaries, some linear solenoids are unidirectional and some are bidirectional. Linear solenoids are usually classified as pull (the electromagnetic path pulls a plunger into the solenoid body) or a push type where the plunger / shaft is pushed out of the case. Many have a spring return to bring the plunger or plunger and shaft back to the home position. Linear solenoids are less complex devices and are significantly less expensive than rotary products. They also offer fewer life cycles and sometimes tend to be larger. Linear solenoids are found in many varieties, many sizes and configurations.
