Patent GB-379416-A (GB)
Title: Improvements in or relating to automatic compressed air brakes for railway vehicles
IPC: B60T15/30
Filed: 1931-06-10
Abstract: 379,416. Fluid-pressure brakes. SOC. ITALIANA E. BREDA, 9, Via Bordoni, Milan, Italy. June 10, 1931, No. 16947. Convention date, June 10, 1930. [Class 103 (i).] Triple valve mechanism for automatic compressed air brakes of the kind controlled by the pressures in chambers connected to the brake pipe and brake cylinder acting together in opposition to the constant pressure in a third chamber comprises an auxiliary valve controlled by the opposed pressures in the brake pipe and the auxiliary reservoir adapted in release to connect the chambers and reservoir in series and to disconnect them from one another during an application. The device includes:-(1) the main valve Y comprising pistons 12, 6 subject to constant pressure in chamber F, to brake-pipe pressure in chamber B, to atmosphere in chamber G<1> and to brakecylinder pressure in chamber G, the piston 6 operating supply and exhaust valves 3, 27 for the brake cylinder, (2) the auxiliary valve X above referred to and which also vents the train pipe in an application, (3) the valve Z which restricts the passage to the brake cylinder when the pressure reaches a predetermined value and which also isolates the constant pressure chamber F until the brake-cylinder pressure in release has fallen to a low value. (4) a hand cock 20 for cutting in an additional brake cylinder and for varying the supply and exhaust passages at the same time. In running conditions, the parts are in the position shown, except that the valves 5, 9 of the device Z are lifted by the spring 17 acting on the piston 7 ; the chamber B is thus connected to the brake pipe 21 by passage 22 and restriction 16 ; the auxiliary reservoir S is supplied from the brake pipe through the chamber B, passages 28, 29, the cavity 30 of the valve 2 and chamber C of this valve ; the chamber F is supplied through chamber C, passage 31, retaining valve 5 and passage 32 ; the accelerating chamber 8 is connected by passages 24, 4, 44 to chamber G and thus to atmosphere by passages 33, 25 ; the brake cylinder 35<1> is connected to atmosphere by passages 35, 34, chamber G and passages 33, 25. With the cock 20 in the position shown, the brake-cylinder 36<1> is cut out. When the brake-pipe pressure is reduced to apply the brakes, the piston 1 of the device X moves to the right the restricted passage 16, delaying the movement of the piston 12. The valve 2 in its right-hand position vents the brake pipe to the accelerating chamber 8 through passages 23, 4, 24 and blanks the passages 29, 31 thus cutting off the auxiliary reservoir S from chambers F, B and the brake pipe. The effective capacity of chamber B is thus reduced and the piston 12 rendered sensitive to brakepipe pressure variations. By the consequent upward movement of pistons 12, 6, the exhaust valve 27 is closed and the valve 3 lifted to supply the brake cylinder from the auxiliary reservoir through passages 18, 34, and at first both through valve 9 and a restricted passage 11. When the brake-cylinder pressure rises sufficiently to overcome the spring 17 the piston 7 is depressed, the valve 9 closes and the supply is continued only through the passage 11. The depression of the piston 7 also seats the valve 5. If the brake-pipe pressure reduction is stopped, the pistons 12, 6 are depressed when the brake-cylinder pressure on the piston 6 together with the brake-pipe pressure on piston 12 equals the constant pressure on the piston 12. The supply valve 3 is thus seated and due to a lost-motion connection between the valves, the exhaust valve 27 remains closed. The brake-cylinder pressure may thus be gradually increased and it may also be gradually decreased by successive increases in brake-pipe pressure, the valve 27 being unseated to allow air to escape through passages 34, 33, 25 at each stage. During the release operation the valve 2 is returned so that the auxiliary reservoir is simultaneously recharged. Somewhat before the brake-pipe pressure reaches its normal value the piston 7 rises and the opening of the valve 5 thereby enables the pressure in the chamber F to equalize with that in the auxiliary reservoir S and chamber B with consequent complete release of the brakecylinder pressure. With the parts in the full-release position, the pressure in the several chambers and in the reservoir may be reduced by a slow-reduction of brake-pipe pressure without applying the brakes but if this is done with the brakes applied and with the valve 2 in the left-hand position, and both the valves 3, 27 closed, the pistons 12, 6 move alternately from the neutral to the upper supply position until the pressure in the brake cylinder is a maximum when they remain in the upper position and since in this position the packing 40 on the piston-rod 15 closes the passage 29, further fall in the brake-pipe pressure moves the valve 2 to the right-hand position. The cock 20 is in three coaxial sections as shown, and when it is given a partial anticlockwise turn so as to register the passage 20b with the passage 41 and the passage 20c with the passage 36, the additional brake cylinder 36<1> is supplied from the passage 34 both through the valve 9 and passage 11 and passages 42, 20c, 36, and also through the passage 41, a restricted port between the passages 20b, 20a and passages 20c, 36. In this position of the cock also, an additional exhaust passage 19, 37 for the cylinders is opened and as a greater quantity of air is drawn from the reservoir S with the two cylinders in use, the restriction 16 in the brake-pipe passage is bypassed through the passage 39 and the middle section of the cock.