The difference between proportional valve and servo valve

For the proportional valve electrical feedback, when the input signal, the main spool drive displacement sensor is connected with the motor, when the displacement signal and the feedback signal is equal to the given, the main spool proportional valve stop motion, reached a new equilibrium position of the servo valve, the valve to maintain a certain output;

Servo valve has two kinds of mechanical feedback and electrical feedback, general electric feedback servo valve frequency response is high, mechanical feedback servo valve frequency response is slightly lower, the action process and the proportion of the valve is basically the same.

The difference of the ratio of the valve: higher input power, basically in a few hundred Ma to 1 amperes, and servo valve input power is small, basically in the tens of milliamperes; the control precision of the proportional valve is slightly lower than the hysteresis of servo valve, servo valve control precision is high, but also for high oil.

I understand from the spool proportional valve structure on the electromagnetic force and liquid pressure and spring force to achieve a balance, and the servo valve is on the liquid pressure to balance, so there is no advantage in the control of proportional valve with large flow and high pressure; the earliest products are proportional valve is open, this should be the reason why called proportional valve; servo valve used in the application, more widely, not only can be used for accurate position, speed control, also with follow-up action, so as to help you open the car is a servo system, it is difficult to achieve proportional valve.

The cylinder moves up and down through the valve in different position so that the oil passage switching, this valve uses the ordinary valve can be achieved, and the servo proportional valve or function can not only control the direction of the cylinder, can accurately control valve opening, which can precisely control the flow (working condition remains unchanged below).

It can only be decided whether the precise feedback valve in place you mentioned valve, but not the state of the control system, because even if the valve opening is accurate, but the real to the actuator affects the flow by pump pressure, pipe consumption, load change and so on many factors, thus to achieve the position or precise speed control. In addition, also need a loop system to avoid obstacle - ring, according to the position and speed, now forming speed and position control board to achieve. You say "do exactly just valve itself, the controlled object is not easy, this is true, but the displacement is not the displacement servo valve, because the valve opening oil port after if not in motion, the actuator will always keep moving trend, like home unscrew the faucet, the water will always flow.

Proportional valve does not have the servo valve spool position to avoid the ring, it is to rely on the larger, precise control of the current proportional to the proportion of the spool valve to control the relative position of the valve and the design of a simplified form. Proportional valve does not have a fixed actuator, precise position and speed control system is also needed to avoid the ring.

2 proportional valve and servo valve are not required amplifier. Is the input control signal 4-20MA or 0-10V? Is not the -10V-+10V is that its action is to rely on the direction of the two coils to change the oil circuit to achieve, rather than by its input control signal to achieve, is it so?

Proportional valve and servo valve control signal input 4-20MA, 0-10V, -10V-+10V, in which the current input signal interference, but the price is expensive, the internal coil can be one or two, many three valve with a coil, by inverting voltage control on both sides of the position, three position valve more the two coil arrangement on both sides of the three valve, but the coil can be controlled separately, can also be connected in series or parallel control. In fact, the proportional valve and servo valve it is difficult to distinguish, may drive mode is the only difference is the servo valve torque motor, proportional valve is proportional servo valve coil, nozzle baffle, high response, proportional valve is the valve, but when it comes to control precision, proportional valve may be high, especially in the bipolar feedback valve. Because the feedback is very proportional pilot valve electric displacement sensor, and the servo valve is a mechanical feedback rod, so in some parameters such as repeatability, hysteresis, linearity of proportional valve than the servo valve, servo valve is better but the curve on the BODE chart.

Proportional valve and servo valve control signal input if the potentiometer input of many 0-5V or -5V-+5V, by changing the ratio of gain adjusting amplifier on the 0-10V, proportional valve and servo valve can also be an external and internal feedback feedback control requirements is not very high in some occasions can be used in the feedback valve and the valve under the superposition of a differential pressure compensator independent of external pressure speed control, if used in the outer loop, then the proportional valve plus a PID control board, the price is very expensive, in some large flow casting machine (4000L/ MIN-12000L/MIN), the proportional servo valve is in the closed loop poles, because the outer ring late.

Proportional valve has a larger zero dead zone (about 20%), while the servo valve is No. From the control, the proportional valve is not suitable for position control.