How do I recognize a good Hydraulic Servovalve? It is probably the frequency response but what do I have to look for in these diagrams?

Is it correct to assume that the higher the frequency at a given amplitude ratio (i.e. -6dB) the better the dynamic behaviour?

What about the phase shift?

  • 2
    $\begingroup$ The best servovalve (or any other component) is going to be the one that most closely matches your requirements. $\endgroup$
    – DLS3141
    Jun 15, 2016 at 14:31
  • 1
    $\begingroup$ There are probably some generic figures of merit, but if you could explain what you are planning to use the valve for, or at least roughly what size you are looking at, that might help people give better advice. $\endgroup$
    – Ethan48
    Jun 15, 2016 at 22:44
  • $\begingroup$ I am just looking for some general Information for various applications. Lets say I need a Size 16 valve. I just have problems understanding the frequency response. If I figure out on how to use this graph to make a statement whether this valve is useful or not for a given application it would help a lot $\endgroup$ Jun 16, 2016 at 7:48

1 Answer 1


You can consider the frequency response as response of a low pass filter.

For one rough example,

When cut-off freq(freq at -6dB) is 50Hz, If you want to control the valve as 100Hz speed(roughly open and close in 0.01 second), the valve is not suitable for your application, because the valve will filter your input from near 50Hz.

If you want to control the valve on 5Hz(open and close in 0.2 second), the valve will be sufficient, in terms of valve response, because 5Hz is in the bandwidth of the filter.

  • $\begingroup$ This is exactly what i was looking for. Thank you for your great explanation. One Question left ... Is the cut off frequency always -6dB? $\endgroup$ Jun 16, 2016 at 13:09
  • $\begingroup$ -6dB is a broadly used conventional standard, not absolute criterion. But, generally, after -6dB, gain is greatly decayed, so that i think -6dB is reasonable standard. $\endgroup$
    – KKS
    Jun 16, 2016 at 13:49

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