All the systems considered in the previous sections have been concerned with the control of: (a) speed, (b) pressure and (c) direction. Many of the systems had inherent feedback loops due to leakage or compressibility, but such feedback did not directly assist the control system in performing its function. Some of the systems, e.g. pressure compensated speed control valve, had deliberate feedback loops without which the control would not have been possible. Further systems will now be considered which involve deliberate feedback loops and consideration will be given to position control.
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