Analysis on the Central Function of Directional Valve

Abstract: This article describes the median performance, structural characteristics, and performance characteristics of various types of Directional Control Valves. It also illustrates the importance of using a mid-position selector valve. The valve is by virtue of the relative movement between the spool valve and the valve body, so that the oil connected to the valve body to achieve hydraulic oil flow, cut off and commutation. The central function of the directional control valve is that the valve in the selector valve is in the middle position or in the original position. The connection form of each port in the valve reflects the control function of the directional control valve. The use of different types of spool valve will directly affect the working condition of the actuator. Therefore, in the construction machinery hydraulic system design, must be based on the working characteristics of the machinery to select the appropriate mid-function reversing valve. The median can be O, H, X, M, Y, P, J, C, K and so on. First, the O-type symbol for which P said the inlet, T said back to the oil port, A, B said the working port. Structural features: In the middle, the oil ports are completely closed and the oil is not circulated. Features: 1, the work of the device, back to the oil ports are closed, the working mechanism can be fixed in any position stationary, even if there is no external force to move the work organization or rotation, which can not be used with a hand-cranked mechanism. 2, from stop to start relatively stable, because the working body back to the oil chamber filled with oil, can play a buffer role, when the pressure oil to promote work institutions began to exercise, due to the impact of oil resistance and its speed will not be too fast, the system Dynamic inertia caused by hydraulic inertia greater impact. 3, the pump can not be unloaded. 4, high-precision reversing position. Second, the H-type symbol for the structural characteristics: In the median, all the ports fully open, the system no oil pressure. Features: 1, oil inlet P, oil return port T and work port A, B all connected, the working mechanism into a floating state, can exercise under the force of external force, can be used with hand-cranked institutions. 2, hydraulic pump can unload. 3, from the stop to start a shock. Because the work of the body back to the oil chamber when the oil has been back to the tank, no oil from the buffer. Brake port interoperability, so the brake is more stable than the O-type. 4, for the single-rod double-acting cylinder, due to the effective area of the piston on both sides of the range, thus using this function of the spool can not fully guarantee the piston is stopped. Third, the M-type symbol for the structural features: In the median, the working oil ports A, B closed, into the oil port P, back to the oil port T directly connected. Features: 1, due to the working port A, B closed, the working body can be kept at rest. 2, hydraulic pump can unload. 3, can not be used for institutions with hand-cranked device. 4, from stop to start relatively stable. 5, brake inertia caused by hydraulic inertia greater impact. 6, can be used to unload the hydraulic cylinder hydraulic cylinder lock circuit. Fourth, the Y-type symbol for the structural characteristics: In the median, the oil inlet P is closed, the working oil ports A, B and the return port T connected. Features: 1, because the working port A, B and the return port T connected to the working body in a floating state, with the role of external forces and movement, can be used with hand-cranked institutions. 2, from stop to start some impact, from rest to start the impact, braking performance between 0 and H-type. 3, the pump can not be unloaded. Five, P-type symbol for the structural features: In the middle, the return port T is closed, the inlet port P and work port A, B are connected. Features: 1, for the same diameter double-rod double-acting cylinder, the hydraulic pressure on both ends of the piston balance each other, the working body can stop moving. It can also be used with a mechanism with a hand crank. However, for single rod or double rod double acting cylinders with different diameters, the working mechanism can not be at rest and form a differential circuit. 2, from stop to start relatively stable, when the brake cylinder two chambers are pressure oil so smooth braking. 3, the pump can not be unloaded. 4, the change of position than the H-type small, widely used. Six, X-type symbol for the structural features: In the median, A, B, P ports are connected with the T back to the oil port. Features: 1, each port and return port T connected, in a semi-open state, due to the existence of throttle, P port also maintain a certain pressure. 2. When the spool valve is moved to the neutral position, the P, A, B and T ports are opened semi-open, so as to avoid the commutation impact caused by the sudden blockage of the pressure port P during the commutation. 3 oil pump can not be unloaded. 4, reversing performance between 0 and H type. Seven, U-shaped structure for the symbol: A, B work port connected, into the oil port P, back to the oil port T closed. Features: 1, due to the work of Port A, B connectivity, working device is in a floating state, can exercise under external force, can be used for institutions with a hand-cranked device. 2, from stop to start relatively stable. 3, the brake is relatively stable. 4, the pump can not unload. Eight, K-type symbol for the structural characteristics: In the median, the inlet port P and working port A and return port T is connected, while the other working port B closed. Features: 1, the pump can unload. 2, performance reversal direction when the two different. Nine, J-type symbols for the structural features: oil inlet P and working oil port A closed, the other working oil port B and return port T connected. Features: 1, the pump can not be unloaded. 2, performance reversal direction when the two different. Ten, C-type symbols for the structural features: oil inlet P and work port A connectivity, and another working port B and back to the oil port T connectivity. Features: The pump can not be unloaded; from stop to start relatively stable, braking a greater impact. Example Analysis 1, the use of the central function of the slide valve design unloading circuit, energy saving. When the spool valve position for the H, K or M-type three-position valve is in position, the pump output of oil directly back to the tank, the unloading circuit to make the pump in the no-load or output power is very small Operating conditions, in order to achieve energy conservation, as shown in Figure 1. This method is simple, but does not apply to a pump drive two or more actuators of the system. 2, the use of the central function of the slide valve designed to brake circuit or locking circuit. In order to stop the moving working mechanism in any desired position and prevent it from moving due to external influences after it stops, a brake circuit can be adopted. The easiest way is to use a reversing valve for braking. For example, a spool valve can be a M or O-type reversing valve that, when it is neutralized, cuts off its inlet and outlet circuits and quickly stops the actuator. As shown in Fig. 2: The loader boom cylinder adopts the brake oil circuit formed by the M type median function reversing valve. The boom can limit itself when the bucket is raised to the highest position and lowered to the lowest horizontal position Brake, the figure back to the limit valve (ie, M-type and H-type four-way valve) is positioned by the ball, when the bucket touch the limit switch to move the switch, the two electromagnetic Valve for the conversion, access to compressed air, the positioning ball back into the tank, the return limit valve will be in the spring to restore the median, cut off the boom cylinder into the oil circuit, so the boom together with the bucket Braking together is limited. 3, the use of H-type, Y-type to achieve floating. For example, when the slewing mechanism of a hydraulic crane rotates under a load, the inertial force will generate a great hydraulic impact if the brake is too harsh. Therefore, it is common to use the slide valve function as a H-type or a Y-type Directional Valve, When the reversing valve is in the neutral position, the swing motor is in a floating state, and then it is stopped by the foot to make it stop smoothly. Figure 2 shows the loader boom cylinder. When the M-type and H-type four-way four-way valve is in the H position, that is, the floating position, then the material can be under the shovel or the formation of the ground, the bucket can rise and fall with the ground level, that is to achieve floating; In the event of a sudden stop working system, you can still put down the bucket smoothly. In the crawler excavator traveling motor directional control valve Y-spool valve function, it can make excavation work in the floating state of the motor does not bear the brake load. 4, the selector valve spool function selection of the right angle roller hydraulic system hydraulic swing speed, the roller vibration performance has a very important impact. Use H-type three-position four-way valve, when the spool valve is in the middle, P, T, A, B four ports connected to form the same communication. Due to the rotational inertia of the exciter, the vibrating wheel will generate residual vibration, resulting in indentation on the surface of the compacted ply, but this has an impact on the compacting effect of the base ply for the roller-based vibratory roller Not big, but also reduces the system's hydraulic impact. In Figure 4, single-frequency double-amplitude vibratory open hydraulic system. Vibratory roller on the road surface, it is required in the process of compaction required to stop vibration or amplitude, the exciter can be 1.5-1.7s time to quickly stop rotating to avoid the moment of the residual vibration to make compaction The surface of the indentation, which affects the quality of compaction. Often used M three-way four-way valve, when the spool in the middle, A, B two work ends, can produce a great back pressure, prompting the motor to overcome the inertia moment of the exciter and rapid stop This avoids the formation of indentations during pavement compaction, but creates a high transient pressure spike in the motor circuit and increases the rate of damage to the motor and other related components. Therefore, it is common to set up two relief valves on the A and B ports of the directional control valve to protect the system. In short, during the selection of the directional valve, be sure to select the appropriate mid-position function according to the working characteristics of the working organization.