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The proportional valve is mostly electrical feedback. When there is a signal input, the main spool drives the displacement sensor connected to it to move. When the feedback displacement signal is equal to the given signal, the main spool stops moving and the proportional valve reaches a new balance of position.
There are two types of servo valves: mechanical feedback and electrical feedback. Generally, the frequency response of the servo valve with electrical feedback is high, and the frequency response of the servo valve with mechanical feedback is slightly lower, and the action is basically the same as that of the proportional valve.
Difference: The input power of the general proportional valve is relatively large, basically ranging from several hundred mA to more than 1 amp, while the input power of the servo valve is relatively small, basically tens of mA. The control accuracy of the proportional valve is slightly lower, and the hysteresis is higher than that of the servo valve. The valve is large, and the control precision of the servo valve is high, but the requirements for the oil are also high.
From the structural understanding, the spool of the proportional valve is balanced by electromagnetic force, hydraulic pressure and spring force. While the servo valve is balanced by hydraulic pressure, so the proportional valve has no advantage in controlling large flow and high pressure. The earliest product of proportional valve is open, which should be the reason why it is called proportional valve. Otherwise, servo valve is more widely used in application, not only can be used for precise position, speed and other control, but also has a follow-up function. The power steering of car is a follow-up servo system, which is difficult to achieve with proportional valves.
The up and down movement of the oil cylinder can be reached by switching the oil circuit by the valve at different positions. This type of valve can be reached by using an ordinary reversing valve, and the function of servo or proportional valve is not only to control the direction of oil cylinder, but also to precisely control the opening of valve, so that the flow can be precisely controlled (the working state remains unchanged).
The feedback of valve can only determine whether the valve is in place accurately, but cannot control the state of system, because even if the opening of valve is accurate, the actual flow into actuator is also affected by pump pressure, pipeline consumption, load changes, etc. Therefore, to reach accurate position of speed control, another loop avoidance loop - system closed loop is required. For position and speed, there are now formed speed and position control boards to achieve. Some people say that "no matter how accurate it is, it is only a problem of the valve itself, but it is difficult for the controlled object", which is true, but the displacement of actuator does not correspond to the displacement of servo spool, because the valve core opens the oil port after the valve is opened. Even if it is not in motion, the actuator will always maintain the motion, just like the faucet at home, the water will flow continuously when you turn it on.
The proportional valve does not have the closed-loop position of spool of the servo valve. It is a simplified design form that relies on a large and precise control of the amount of current supplied to the proportional spool to control the relatively accurate spool position. The proportional valve does not need to be equipped with a fixed actuator, and the precise realization of position and speed control still requires a closed-loop system. For further information about proportional valve, please visit https://www.genndih.com/proportional-pressure-regulator/low-pressure-proportional-regulator-0-8bar.html
Do both proportional valves and servo valves need amplifiers? Is the input control signal 4-20MA or 0-10V? Is there no -10V-+10V, which means that its action direction is realized by the two coils acting respectively to change the oil circuit, not by its input control signal, is that so?
The input control signals of proportional valve and servo valve are 4-20MA, 0-10V, -10V-+10V, among which the current input signal has strong anti-interference, but the corresponding price is expensive, the internal coil can be one or two. Many three-way valve uses only one coil and controls the positions on both sides by voltage inversion. The three-way valve usually has two coils arranged on both sides of the three-way valve, but the coils can be controlled individually or in series or in parallel. In fact, it is difficult to distinguish between proportional valve and servo valve. Maybe the only difference is the driving method. The servo valve is a torque motor, the proportional valve is a proportional coil, the servo valve is a nozzle baffle, the response is high, and the proportional valve is a spool valve, but when it comes to the control accuracy of proportional valves may be higher. Especially in two-pole feedback valves, because the proportional valve feedback of the pilot is an electrical displacement sensor, and the servo valve is a mechanical feedback rod, so some parameters such as repeatability, hysteresis ring, linearity proportional valve is better than servo valve.
There are two types of servo valves: mechanical feedback and electrical feedback. Generally, the frequency response of the servo valve with electrical feedback is high, and the frequency response of the servo valve with mechanical feedback is slightly lower, and the action is basically the same as that of the proportional valve.
Difference: The input power of the general proportional valve is relatively large, basically ranging from several hundred mA to more than 1 amp, while the input power of the servo valve is relatively small, basically tens of mA. The control accuracy of the proportional valve is slightly lower, and the hysteresis is higher than that of the servo valve. The valve is large, and the control precision of the servo valve is high, but the requirements for the oil are also high.
From the structural understanding, the spool of the proportional valve is balanced by electromagnetic force, hydraulic pressure and spring force. While the servo valve is balanced by hydraulic pressure, so the proportional valve has no advantage in controlling large flow and high pressure. The earliest product of proportional valve is open, which should be the reason why it is called proportional valve. Otherwise, servo valve is more widely used in application, not only can be used for precise position, speed and other control, but also has a follow-up function. The power steering of car is a follow-up servo system, which is difficult to achieve with proportional valves.
The up and down movement of the oil cylinder can be reached by switching the oil circuit by the valve at different positions. This type of valve can be reached by using an ordinary reversing valve, and the function of servo or proportional valve is not only to control the direction of oil cylinder, but also to precisely control the opening of valve, so that the flow can be precisely controlled (the working state remains unchanged).
The feedback of valve can only determine whether the valve is in place accurately, but cannot control the state of system, because even if the opening of valve is accurate, the actual flow into actuator is also affected by pump pressure, pipeline consumption, load changes, etc. Therefore, to reach accurate position of speed control, another loop avoidance loop - system closed loop is required. For position and speed, there are now formed speed and position control boards to achieve. Some people say that "no matter how accurate it is, it is only a problem of the valve itself, but it is difficult for the controlled object", which is true, but the displacement of actuator does not correspond to the displacement of servo spool, because the valve core opens the oil port after the valve is opened. Even if it is not in motion, the actuator will always maintain the motion, just like the faucet at home, the water will flow continuously when you turn it on.
The proportional valve does not have the closed-loop position of spool of the servo valve. It is a simplified design form that relies on a large and precise control of the amount of current supplied to the proportional spool to control the relatively accurate spool position. The proportional valve does not need to be equipped with a fixed actuator, and the precise realization of position and speed control still requires a closed-loop system. For further information about proportional valve, please visit https://www.genndih.com/proportional-pressure-regulator/low-pressure-proportional-regulator-0-8bar.html
Do both proportional valves and servo valves need amplifiers? Is the input control signal 4-20MA or 0-10V? Is there no -10V-+10V, which means that its action direction is realized by the two coils acting respectively to change the oil circuit, not by its input control signal, is that so?
The input control signals of proportional valve and servo valve are 4-20MA, 0-10V, -10V-+10V, among which the current input signal has strong anti-interference, but the corresponding price is expensive, the internal coil can be one or two. Many three-way valve uses only one coil and controls the positions on both sides by voltage inversion. The three-way valve usually has two coils arranged on both sides of the three-way valve, but the coils can be controlled individually or in series or in parallel. In fact, it is difficult to distinguish between proportional valve and servo valve. Maybe the only difference is the driving method. The servo valve is a torque motor, the proportional valve is a proportional coil, the servo valve is a nozzle baffle, the response is high, and the proportional valve is a spool valve, but when it comes to the control accuracy of proportional valves may be higher. Especially in two-pole feedback valves, because the proportional valve feedback of the pilot is an electrical displacement sensor, and the servo valve is a mechanical feedback rod, so some parameters such as repeatability, hysteresis ring, linearity proportional valve is better than servo valve.