292,153. Bragg, C., S., and Kliesrath, V. W. June 17, 1927, [Convention date]. Fluid-pressure apparatus more particularly for operating the brakes of motor vehicles is provided with a controlling valve device which is subject to the opposing pressures exerted by a spring or other closing device and a fluid pressure difference acting upon opposite faces of the valve device, the fluid pressure difference normally almost counterbalancing the spring &c. pressure but decreasing as the fluid passes by the valve during the operation of the apparatus so that the resistance to the opening movement of the valve indicates the pressure which is being applied by the piston of the apparatus to the brakes &c. Figs. 2, 3 show one arrangement in which a piston 3 connected to the brakes &c. is normally exposed to vacuum produced by the suction of an internal combustion engine on both sides, air being admitted to one side to apply the brakes. The piston has a hollow piston rod 5 connected at 10 to the brake &c. mechanism and within which slides a tubular, valve rod 20 connected at 29 to the operating pedal. The valve device comprises suction and inlet valves 17, 14 freely mounted on the rod 20 and engageable by collars 20a, 20<b> on the rod for actuating the valves. A spring 19 tends to urge the valves apart. A flat spiral spring 21 interposed between collars on the rods 5, 20 in conjunction it may be with a spring connected to the pedal normally holds the rod 20 in the position shown so as to open the suction valve 16 and permit the inlet valve 14 to close under the action of spring 25. By means of a pipe 32 connected to the intake manifold of the engine, a vacuum is constantly maintained in the forward chamber of the cylinder 1 and with the valve 16 in the open position the rear chamber is also exhausted through the valve chamber 13 and the passage 13<b>. One face of the valve 14 is thus subject to the vacuum in the rear cylinder chamber and the other face to atmospheric pressure admitted by the valve rod 5, apertures 28, and an inlet 11. The valve closing springs 25 and the pedal spring if provided are just sufficient to overcome the maximum fluid pressure difference which acts on the valve 14 when the brakes are released. When the pedal is actuated to apply the brakes, the rod 20 permits the valve 16 to close and open the valve 14 thereby admitting air through the inlet 11, valve rod 20, and the passage 13b to the rear cylinder chamber. If the pedal is held in an intermediate position the movement of the piston 3 re-closes the valve 14 without re-opening the valve 16 and the brakes may thus be held applied at any desired pressure. As the vacuum in the rear cylinder chamber is gradually destroyed, the pressure, of the. springs 25 and the pedal spring is to a continually lesser extent counterbalanced by the fluid pressure difference acting on the valve 14 and the greater becomes the pressure necessary to open this valve. The operator thus obtains an indication of the pressure exerted by the piston 3 on the brakes. This pressure is felt by the operator only as long as the valve is held in the open position. By continued movement of the pedal, the spring 21 is completely compressed and the operator is thus able to exert a direct effort on the brakes. The valves may be arranged in a separate casing external to the cylinder 1. In this case the casing may be coupled to the brake transmission mechanism in such a manner that the valves when opened are re-closed by the movement of the piston and mechanism as described above or as shown in Fig. 6 the valve casing 206 may be connected by a pin-and-slot connection with the brake-shaft 276 and be held against a stop 206<a> by a spring 279 so that it is not moved by the fluid pressure operation of the apparatus, the spring yielding however to enable the application of the direct effort of the operator to the brakes. By means of pipes 1<a>, 1<b>, Fig. 2, provided with cocks 1<c>, 1<d>, the cylinder 1 may be connected to other cylinders provided on the same or different vehicles as described in Specification 252,333. Instead of the operation being effected by vacuum and atmospheric pressure, a source of compressed air may be connected to the inlet 11 the other side of the piston being in this case connected either to the engine suction or to atmosphere.