I have a hydraulically actuated aircraft brake system. Each main landing gear are equipped with brake disk hydraulically operated. The actuation is realized independently for each wheels by means of the correspondent control valve which controls pressure delivery to the brakes. Each brake control valve is connected to each pedal brake. When the pedal brake is depressed, the control valve will open and deliver a variable pressure to the brake adjusted by the pedal angel. The problem is the Brake is too responsive. When the pedal is depressed slightly, the aircraft suddenly stop.

What is the main problem? Is it the hydraulic flow to the brake disk too high?
Can I install a "restrictor valve" from the brake valve to disk to restrict the flow and make the brake smoother? if so, how can i determine the size of the restrictor valve?

or the pressure to disk brake is too high?

enter image description here

the function of accumulator is for emergency

  • $\begingroup$ What is the make, model and year of the airplane? Is it a standard brake system, or modified? Has this problem suddenly started, or has it always been like this? Do both left and right brakes act the same? $\endgroup$
    – GdD
    Apr 27, 2018 at 8:27
  • $\begingroup$ it is a development design. this problem suddenly start when the design is installed and always like this. the left and right act the same $\endgroup$ Apr 27, 2018 at 8:33
  • $\begingroup$ I agree with Frederico, you'll need a valve that controls pressure instead of flow. I am a bit worried about your design in general though, if you loose hydrolic power, you'll loose your brakes too. Do you have backup HPU's and safety systems that can shut down leaking systems so the rest is still working? What else is connected to this system? $\endgroup$
    – Orbit
    Apr 27, 2018 at 11:40

1 Answer 1


the pressure to disk brake is too high?

That is sure, that is the only parameter that can influence how much braking authority you are using.

Given the schematic you posted, my otherwise uninformed opinion (as I don't have pressure measurements, or other data), is that you should investigate your brake valve.

It is probably not providing a sufficient pressure drop even when slightly open. This could be due to the valve model.

Yes, your suggestion to have a restrictor valve (or an O ring inside the pipes) should be a suitable approach, but it depends on the solution you are looking for. The pressure will drop when the brake fluid is moving, but the equilibrium state will not change, if you keep your pedal slightly depressed your aircraft will still come to a complete stop, simply it will do so slightly later.

If your intention is to have the braking authority controlled by the pedal, what you really want is to change the pressure reaching the brake disk with the pedal.
No static solution is viable in that case: you will need a valve that lets you control the pressure received by the brake plate with the pedal deflection, i.e. you probably have to change your brake valve, or you have to install a system that dynamically adjusts the pressure downstream of the brake valve.

  • $\begingroup$ the pedal travel is about 15 degree max, and the plunger is 40 mm. pressure from hydraulic power is 1500 psi max. should i change the valve or just modify the mechanical link between pedal to valve? maybe expand the travel of the pedal? $\endgroup$ Apr 27, 2018 at 9:09
  • $\begingroup$ @RahmatAliAkbar that I cannot answer. It depends on the type of valve, the way the mechanical link works, etc. You will have to decide how exactly to modify your system, either by trial and error, or by having someone with expertise come at your location. $\endgroup$
    – Federico
    Apr 27, 2018 at 9:11

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