The difference between proportional valve and servo valve

The difference between proportional valve and servo valve

The proportional valve is mostly electrical feedback. When there is signal input, the main spool drives the displacement sensor connected to it. When the feedback displacement signal is equal to the given signal, the main spool stops moving and the proportional valve reaches a new balance. Position servo valve, the valve maintains a certain output; the proportional valve is mostly electrical feedback. When there is signal input, the main spool drives the displacement sensor connected to it. When the feedback displacement signal is equal to the given signal, the main spool Stop the movement, the proportional valve reaches a new balanced position servo valve, and the valve maintains a certain output;
The servo valve has two kinds of mechanical feedback and electrical feedback. The frequency response of the servo valve of general electrical feedback is high, the frequency response of the mechanical feedback servo valve is slightly lower, and the action process is basically the same as that of the proportional valve.
The difference: the input power of the general proportional valve is relatively large, basically several hundred milliamperes to more than 1 amp, and the input power of the servo valve is small, basically several tens of milliamperes; the control precision of the proportional valve is slightly lower, and the hysteresis is more servo The valve is large, the servo valve has high control precision, but the requirements for oil are also high.
I understand from the structure that the spool of the proportional valve is balanced by electromagnetic force and hydraulic pressure and spring force, while the servo valve is balanced by hydraulic pressure, so the proportional valve has no advantage in controlling high flow and high pressure; The earliest product with proportional valve is open type, which should be the reason why it is called proportional valve; in application, the servo valve is used more widely, not only for precise position, speed control, but also with action. So the car power steering like you drive is a follow-up servo system, which is difficult to achieve with proportional valves.
Realizing the up and down movement of the cylinder can be realized by switching the oil passage in different positions of the valve. Such a valve can be realized by using a common reversing valve, and the servo or proportional valve can not only control the direction of the cylinder, but also can accurately control. The opening of the valve allows precise control of the flow (the operating state remains the same).
The feedback from the valve you mentioned can only determine whether the valve is in place and does not control the state of the system, because even if the valve opening is accurate, the flow to the actuator is actually affected by the pump pressure, the pipeline, Load changes and many other factors, so to achieve accurate position or speed control, you need another loop avoidance loop - system avoidance loop, for position and speed, there is now a speed and position control board to achieve. What you said is "the exactness of the process is only the problem of the valve itself, but it is not easy for the controlled object." This is true, but the displacement of the actuator does not correspond to the displacement of the servo spool, because the spool is open. Even after the oil port is not moving, the actuator will always maintain the movement, just like the faucet at home, the water will flow when it is unscrewed.
The proportional valve does not have the spool position of the servo valve. It is a simplified design that relies on a large, precise control of the amount of current supplied to the proportional spool to control a relatively accurate spool position. Proportional valves do not require a fixed actuator, and precise position and speed control is required to avoid loops.

2 Proportional valves and servo valves do not require an amplifier. Is its input control signal 4-20MA or 0-10V? Is it true that there is no -10V-+10V? It is said that the action direction is to change the oil path by two coils respectively, instead of being realized by its input control signal. Is this true?

The proportional valve and servo valve input control signals are 4-20MA, 0-10V, -10V-+10V, in which the current input signal is strong against interference, but the corresponding price is expensive, the internal coil can be one or both, and many The three-position valve uses only one coil, and the two sides are controlled by voltage inversion. The three-position valve is more that two coils are arranged on both sides of the three-position valve, but the coils can be controlled individually or in series or in parallel. In fact, the proportional valve and the servo valve are difficult to distinguish now. The possible driving method is the only difference. The servo valve is the torque motor, the proportional valve is the proportional coil, the servo valve is the nozzle stop plate, and the response valve is the high point. The proportional valve is the slide valve, but when it comes to Control accuracy, proportional valve may be higher, especially in the two-pole feedback valve, because the proportional valve feedback of the pilot pole is an electric displacement sensor, and the servo valve is a mechanical feedback rod, so in some parameters such as repeatability, lag The ring, linearity proportional valve is better than the servo valve, but the curve servo valve on the BODE diagram is better.
Proportional valve and servo valve input control signals are 0-5V or -5V-+5V if they are input through the potentiometer. By changing the proportional gain adjustment on the amplifier to 0-10V, the proportional valve and servo valve can be internal feedback. External feedback can be externally used. In some occasions where the control requirements are not very high, an internal feedback valve can be used and a differential pressure compensator is superimposed under the valve to achieve speed control independent of external pressure. If an external closed loop is used, the proportional valve is added. A PID control board is very expensive. On some die-casting machines with a large flow rate (4000L/MIN-12000L/MIN), the proportional servo valves are closed loops in the two poles because the outer ring is too late.
The proportional valve has a larger zero dead zone (about 20%), while the servo valve does not. Proportional valves are not suitable for position control from control.

Keywords: proportional valve, servo valve, servo hydraulic system, servo hydraulic cylinder
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  • Formula:  C14H9NO2
  • CAS Registry Number:  82-45-1
  • Other names:  Anthraquinone , 1-amino-; α-Aminoanthraquinone; α-Anthraquinonylamine; C.I. 37275; Diazo Fast Red AL ; 1-Amino-9 , 10-anthraquinone ; 1-Aminoanthraquinone; 1-Aminoanthrachinon; 1-amino- 9, 10-Anthracenedione ; Smoke Orange G; 9, 10-dioxo-9 ,10-dihydro-1-anthraceneamine; NSC 30415; NSC 458
  • Specifications

Melting Point

252°C to 255°C



MDL Number


Merck Index


Solubility Information

Soluble in alcohol, benzene, chlroform, ether, glacial acetic acid, HCl



Molecular Weight (g/mol)


Formula Weight


Chemical Name or Material


Molecular Formula





1-AMINOANTHRAQUINONE , Diazo Fast Red AL , anthraquinone, 1-amino, 1-Amino anthraquinone, 1-aminoanthrachinon, 1-amino-anthraquinone, 9,10-anthracenedione, 1-amino, alpha-Aminoanthraquinone, 1-amino-9,10-anthraquinone, 1-amino-9,10-anthracenedione

InChI Key



1-aminoanthracene-9 , 10-dione

Percent Purity




9,10-Anthracenedione, 1-amino-,Azoic Diazo No. 36,Fast Red AL,1-aminoanthraquinone, C14H9NO2,1-Amino-9,10-anthraquinone,alpha-Aminoanthraquinone

Jinan Forever Chemical Co., Ltd. ,