Working principle of hydraulic directional valve
The number of passages held by the hydraulic directional valve according to the directional valve is different: two-way, three-way, four-way and five-way. The absolute movement of the valve body with the wrong spool is used to make the oil road traffic, shut off or change the direction of oil flow, so that the name of the hydraulic pressure fulfillment element and its driving mechanism can support, end or change the direction of movement.
1. The principle of working interest
Figure 4-3a shows the working principle diagram of the spool valve, when the spool moves to the right by a certain interval, the pressure oil input by the hydraulic pump wins from the P port of the valve through the A port to the right of the hydraulic cylinder The oil in the right cavity of the hydraulic cylinder returns to the tank through the B port source, and the piston of the hydraulic cylinder moves to the right; conversely, if the spool moves to a certain interval to the right, the flow of fluid reverses and the piston moves to the left. Figure 4-3b is its graphical symbol.
2. The structure of the directional valve
1) Manual directional valve
Apply manual lever back to change the status of the spool. There are two types of active spring return (a) and spring steel ball (b) positioning.
2) Flexible directional valve
The flexible directional valve is also known as a stroke valve. It is important to control the stop of mechanical moving parts. It also helps the iron or concave wheel installed on the table to force the valve core to move, so as to control the direction of the liquid flow.
3) Solenoid directional valve
Disadvantages: The electromagnet is used to energize, disengage, and release, and indirectly advance the spool to control the flow direction. It is not a question mark conversion element between electrical disassembly and hydraulic system.
Figure 4-9a shows the structure of the two-position three-way exchange solenoid valve. In the position shown in the figure, the ports P and A are connected, and the port B is closed; when the electromagnet is energized to call, the lever 1 pulls the spool 2 to Zuo Rui, then the oil core P and A are disconnected, and B Connected. When the solenoid is de-energized and released, the spring 3 pushes the spool to reset. Figure 4-9b replaces the graphic symbol.
4) Hydraulic directional valve
The directional valve that changes the position of the spool by using the pressure oil in the oil circuit. The spool is not moved by the pressure difference of the oil outside the dilute seal cavity at its two ends. As shown in the figure, when the pressure oil enters the left cavity of the spool from K2, K1 is connected to the return oil, and the spool moves to the right, so that P and B are connected, and A and T are connected; when K1 traffic pressure oil, K2 traffic returns Oil, the spool moves to the left, so that P and A communicate, and B and T communicate; when both K1 and K2 return to the oil, the spool returns to the two ends.
5) Electro-hydraulic directional valve
It is composed of electromagnetic astringent valve and hydraulic slide valve. The solenoid valve can be used as a guide to change the direction of liquid flow, thus changing the position of the spool of the hydraulic spool. Used outside Daxi type hydraulic equipment.
3. Performance and characteristics of directional valve
1) The median performance of the spool
Various control methods of three-position four-way and three-position five-way directional spool valve, when the spool is at both ends, the connection of each oil port is called the west position performance of the replacement directional valve. Rarely used are "O" type, "H" type, "P" type, K "type," M "type, etc.
When analysing and choosing the neutral performance of the three-position directional valve, we usually consider:
(1) When the system pressure holding P heart is blocked, the system pressure holding, the hydraulic pump is used for multi-cylinder disassembly.
(2) The unloading and unloading of the P system is smoothly connected to the T port, and the system is unloaded. (HKXM type)
(3) The commutation is stable and the accuracy A and B are blocked. The impact of the commutation process is difficult, and the commutation is unstable, but the accuracy is high.
(4) When the safety valve is in the external position, a cavity of the hydraulic oil cylinder is connected to the oil tank. When sealing, there is sufficient oil to slowly rush and the bearing is unstable.
(5) The hydraulic cylinder floats and ends in the unintentional position
2) Liquid energy of astringent valve
According to the law of kinetic mass of liquid flow, the hydraulic force acting on the spool when the oil passes through the power directional valve has two types: steady-state fluid power and transient fluid power.
(1) Steady state liquid energy: before the spool is moved, before the teeth are fixed, the kinetic quality changes when the liquid flows to the valve core and the force is used under the spool without the tendency to close the valve port, and the source quality of the valve Irrelevant.
(2) Transient fluid energy: during the movement of the spool valve, the force acting on the spool due to the deceleration or acceleration of the valve cavity fluid source is independent of the speed of movement.
3) The sight of hydraulic card pine
Casone fruit: dirt enters the gap; the warmth is reduced and the spool shrinks; but the guest has to play a role in the radial imbalance force caused by the change in the shape and common mouth of the non-slide valve pair. Its important include:
a How much is the shape error between the valve core and the valve body, the shaft mouth line is flat but does not sink
b The spool is reduced due to work error and there is no inverted cone, and the shaft line is flat but not sinking
c No spool rises in name
Ways to increase the radial imbalance force:
1) Improve production and disassembly accuracy
2) Closed annular equalizing groove under the spool
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