Abstract: A load pressure feedback system having at least one control valve for controlling a manipulator comprising a load arm which is pivotally connected to a base member, and a control member having a manually movable control arm which is of the same configuration as but on a smaller scale than the load arm. The pivots or rotary mountings of the load arm and control arm are connected together and controlled by a load pressure feedback system comprising a valve having a hydraulic pilot control member. The load pressures at measuring locations of the apparatus are applied to the inlet of at least one throttle aperture and the level of the control pressures is determined by the cross-sectional areas of the throttle aperture and a screw-in control aperture in the valve. At least one control piston is subjected, on the one hand, to the load pressures and on the other hand to the control pressures.