What is the difference between a closed loop and an open loop circuit in hydraulics?
Same as it is in electricity… feedback. Part of the output is fed back to the input side, in the opposite sense and in proportion to the output. Used to control the output to stop it getting too excessive or building up too quickly. Minty has the system a little wrong in that you can use a closed loop with a centre open valve. If you feed the pressure to both the cap and rod of a jack it can be finely balanced and only a little extra force on one side or the other will make it move, the amount of movement will be proportional to the force and then feedback is used to integrate acceleration to get speed and integrated again to get distance so you can tell how far the jack has moved. This is the basic principle of a hydraulic motion platform that flight simulators use, including the rides that can be seen on many fairgrounds. The centre open valve acts in a similar way to an electronic transistor where a small amount of energy can control a much larger amount.
