Modulator assemblies for vehicle anti-skid braking systems

An anti-skid brake control system comprising a wheel having a hydraulic brake, means to sense the presence of skid conditions at the wheel during braking and thereupon to produce a skid signal, a movable wall separating first and second chambers, said first chamber being connected to the hydraulic brake and the movable wall being arranged to increase the volume of said first chamber in response to the skid signal so as to relieve the brake pressure at the braked wheel, a regulator arranged to regulate flow of fluid to said second chamber on cessation of the skid signal such that the movable wall is thereby moved progressively to reduce the volume of said first chamber so as to re-apply the brake pressure at a controlled rate, the regulator comprising a first restriction of predetermined size connected in series with a second restriction defined between two relatively movable members, relative movement of the members being controlled by the difference in fluid pressure across the first restriction such that an increase in this pressure difference causes a reduction in the size of the second restriction, a reservoir, a substantially unrestricted dump passage connecting said second chamber to said reservoir, and a dump valve member controlling said dump passage whereby on opening of said dump valve member in response to the skid signal substantially unrestricted flow of fluid is permitted from said second chamber to said reservoir.