Solenoid valve definition, classification and principles
Solenoid valve is used to control the fluid automatic based components, belonging to the actuator; are not limited to hydraulic, pneumatic. Solenoid valve is used to control the hydraulic flow direction, the plant's mechanical devices are general controled by the hydraulic steel, so it will use solenoid valve. Working principles: there is closed cavity in solenoid valve, in a different location it has been opened a hole, each hole is leading to a different pipeline, the middle cavity is valve, two sides are two electromagnets, which side of magnet coil is powered, the body will be attracted to which side, through controlling body movement to block or leak oil in a different row of holes, but oil feed hole is always open, the hydraulic oil will enter a different row tubes, and then through the oil pressure to promote the cylinder piston, piston also drives piston rod, piston rod drives mechanism moving. This through controlling the electromagnet current controls the mechanical movement.
classification
From the principle of at home and abroad the solenoid valve is divided into three categories (ie: direct-acting type, sub-step direct-acting type, pilot-type), while from the different disc structures and materials and the principles, it is divided into six branch sub-groups (direct-acting diaphragm structure, sub-step re-sheet structure, the pilot diaphragm structure, and straight-acting piston structure, sub-step straight-acting piston structure, the pilot piston structure).
①direct-acting solenoid valve
Principle: when power on, the electromagnetic coil produces electromagnetic force to lift the closed piece from the seat, the valve opens; power off, the electromagnetic force disappears, the spring presses the closed piece on the seat, the valve closes.
Features: In the vacuum, negative pressure, zero pressure can also normal work, but the diameter is generally not more than 25mm.
②sub-step direct-acting type
Principle: It is a combined theory of direct-acting and pilot-style, when the entrances and exits with no differential pressure, when power on, the electromagnetic force directly raised up the pilot valve and main valve closed pieces in turn, the valve opens. When the entrances and exits achieve the start pressure differential, when power on, the electromagnetic force pilot a small valve, main valve down cavity pressure increases, upper cavity pressure drops, thus use the pressure differential to open the main valve upward; when power off, the pilot valve uses spring force or medium pressure to promote closed pieces, moving down, so that the valve closes.
Features: In the zero-pressure or vacuum, high pressure can also be acted, but the power is larger, which calls for horizontal installation.
③pilot-type solenoid valve
Principle: when power on, the electromagnetic force opens the pilot hole, the upper cavuty pressure drops rapidly to form up-low and down-high pressure differential around the closed piece, the fluid pressure promotes closed piece moving upward, the valve opens; when power off, the spring force closes pilot hole, the inlet pressure through the bypass hole quickly formed up-high and down-low pressure differential around the closed piece, the fluid pressure promotes closed pieces moving down, close the valve.
Features: fluid pressure scope limit is higher, can be arbitrarily install (need to customize), but must meet the conditions of fluid pressure. In the use, should be more considered some of its features, such as media characteristics, ambient temperature, operating frequency, power and other factors.
