How is the direction of the hydraulic fluid changed, so that components and actuators (cylinders and pistons) can move backwards and forwards?

  • 1
    $\begingroup$ Aircraft use hydraulic systems, but not really sure this is aircraft related. $\endgroup$
    – FreeMan
    Oct 6, 2017 at 17:47
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    $\begingroup$ This is really a very basic mechanical engineering question. $\endgroup$ Oct 6, 2017 at 18:01
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    $\begingroup$ Using hydraulic valves. $\endgroup$
    – Lnafziger
    Oct 6, 2017 at 18:16
  • 2
    $\begingroup$ Take a look at How Do Hydraulic Cylinders Work? $\endgroup$ Oct 6, 2017 at 19:45
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    $\begingroup$ The fluid direction does not change, there is a valve that either directs fluid to the extension side of the piston, or the retraction side of the piston. The "non-pressure" side of the piston is also directed back to the tank so that there isn't (much) back-pressure on the other side of the piston. $\endgroup$
    – Ron Beyer
    Oct 6, 2017 at 21:09

1 Answer 1


The direction of travel is controlled by a directional control valve for a double acting cylinder.

enter image description here

The red line is high pressure from hydraulic pump. when the high pressure fluid is entering the right chamber and push the actuator piston to left. The low pressure fluid in left chamber (blue line) will leave the actuator and return to reservoir.

If we rotated/move the directional control valve clockwise it will look like the figure below :

enter image description here

The high pressure will enter the left chamber and move the actuator piston to right

  • $\begingroup$ Downvoted as it clearly need editing efforts before reaching quality standard as defined in the help center $\endgroup$
    – Manu H
    Apr 27, 2018 at 6:00
  • $\begingroup$ @ManuH got edited, see if you want to rethink your vote $\endgroup$
    – Federico
    Apr 27, 2018 at 7:03
  • $\begingroup$ I agree ilustration improve the answer's quality, but it still lack editing efforts. e.g. the first sentence is not a sentence. $\endgroup$
    – Manu H
    Apr 27, 2018 at 11:43
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    $\begingroup$ @ManuH Then edit it? $\endgroup$
    – vidarlo
    Apr 27, 2018 at 12:35
  • $\begingroup$ Great diagrams! $\endgroup$
    – zeta-band
    Apr 27, 2018 at 21:49

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