The principle of solenoid valve can be divided into three categories: direct acting, step-by-step direct acting and pilot operated. Today EVP vacuum pump manufacturers for you to sort out the principle and classification of solenoid valve, let’s get to know!
Direct acting solenoid valve
There are two types: normally closed type and normally open type. When the normally closed type is powered off, it is in a closed state. When the coil is powered on, it generates electromagnetic force, which makes the moving iron core overcome the spring force to close the valve directly with the static iron core. When the coil is powered off, the electromagnetic force disappears, and the moving iron core resets under the action of the spring force, which directly closes the valve port. The medium is not available. It is simple in structure, reliable in action and works normally under zero pressure difference and micro vacuum. The normally open type is the opposite. For example, solenoid valve with flow diameter less than φ 6.
Principle of direct acting solenoid valve: when the normally closed type is energized, the solenoid coil generates electromagnetic force to lift the open part from the valve seat and open the valve; when the power is off, the electromagnetic force disappears, and the spring presses the open part on the valve seat and the valve opens. (normally open type is the opposite)
Features of direct acting solenoid valve: it can work normally in vacuum, negative pressure and zero pressure, but its diameter is generally less than 25mm.
Step by step direct acting solenoid valve
This kind of valve is connected with the primary valve and the secondary valve. The main valve and the pilot valve step by step make the electromagnetic force and pressure difference directly open the main valve port. When the coil is electrified, electromagnetic force is generated to make the moving iron core and the static iron core close. The pilot valve port is opened and the pilot valve port is set on the main valve port, and the moving iron core is connected with the main valve core. At this time, the pressure in the upper chamber of the main valve is unloaded through the pilot valve port. Under the simultaneous action of pressure difference and electromagnetic force, the main valve core moves upward to open the medium flow of the main valve. When the coil is powered off, the electromagnetic force disappears. At this time, the moving iron core closes the pilot valve hole under the action of self weight and spring force. At this time, the medium enters the upper chamber of the main valve core in the balance hole, which increases the pressure of the upper chamber. At this time, the main valve is closed under the action of spring return and pressure, and the medium is cut off. The structure is reasonable, the action is reliable, and the work is reliable when the pressure difference is zero.
Principle of step-by-step direct acting solenoid valve: it is a principle of combination of direct acting and pilot type. When there is no pressure difference between the inlet and the outlet, the electromagnetic force directly lifts the small pilot valve and the main valve closing piece up one by one after power on, and the valve opens. When the pressure difference between the inlet and the outlet reaches the starting pressure, the small solenoid pilot valve will increase the pressure in the lower chamber of the main valve and decrease the pressure in the upper chamber after being powered on, so as to push the main valve upward by using the pressure difference; when the power is off, the pilot valve will use the spring force or the medium pressure to push the closure piece and move downward to close the valve.
Features of step-by-step direct acting solenoid valve: it can also operate when there is no pressure difference or vacuum or high pressure, but the power is large, so it must be installed horizontally.
Pilot operated solenoid valve
The solenoid valve is composed of the pilot valve and the main valve core, which are connected to form a channel combination; the normally closed valve is in a closed state when it is not energized. When the coil is energized, the generated magnetic force makes the moving iron core and the static iron core close, the pilot valve port opens, and the medium flows to the outlet. At this time, the upper chamber pressure of the main valve core decreases, which is lower than the pressure at the inlet side, forming a differential pressure to overcome the spring resistance and then move upward, so as to open the main valve port, and the medium flows. When the coil is powered off, the magnetic force disappears, and the moving iron core resets and closes the pilot port under the action of spring force. At this time, the medium flows in from the balance hole, the upper chamber pressure of the main valve core increases, and moves downward under the action of spring force to close the main valve port. The normally open principle is the opposite.
Principle of pilot solenoid valve: when energized, the electromagnetic force opens the pilot hole, and the pressure in the upper chamber drops rapidly. A high and low pressure difference is formed around the closing piece. The fluid pressure pushes the closing piece to move upward, and the valve opens. When the power is off, the spring force closes the pilot hole, and the inlet pressure quickly forms a low and high pressure difference around the closing piece through the bypass hole. The fluid pressure pushes Move the closing part downward to close the valve.
Features of pilot solenoid valve: small volume, low power, high upper limit of fluid pressure range, which can be installed arbitrarily (customized) but must meet the condition of fluid pressure difference.
The solenoid valve is divided into six sub categories according to the difference in valve structure and material and the difference in principle:
Direct acting diaphragm structure, step-by-step direct acting diaphragm structure, pilot diaphragm structure, direct acting piston structure, step-by-step direct acting piston structure and pilot piston structure.
Solenoid valves are classified by function:
Water solenoid valve, steam solenoid valve, refrigeration solenoid valve, low temperature solenoid valve, gas solenoid valve, fire solenoid valve, ammonia solenoid valve, gas solenoid valve, liquid solenoid valve, micro solenoid valve, pulse solenoid valve, hydraulic solenoid valve normally open solenoid valve, oil solenoid valve, DC solenoid valve, high pressure solenoid valve, explosion-proof solenoid valve, etc.