Patent GB-190722736-A (GB)
Title: Improvements in Air Brake Systems.
Filed: 1907-10-15
Granted: 1908-08-20
Abstract: 22,736. British Thomson-Houston Co., [General Electric Co.]. Oct. 15. Brakes.-In an airbrake system having the braking pressure proportional to the reduction of train-pipe pressure, and the release proportional to the recharging of the train-pipe, the main valve chamber is supplied with air at a constant pressure from a reservoir, through a valve controlled by a piston operated on one side by the constant pressure of the reservoir, which is balanced by the combined pressures of the air in the main valve chamber and of the air admitted to the brake cylinder. The main reservoir 5 supplies compressed air to the service reservoir 8 on the engine through a reducing - valve 6 and clack valve 7, and to the service reservoirs on the cars through a pipe 9, so that a constant pressure is maintained in the reservoirs independently of the train-pipe 11. The main valve 13', Fig. 3, has a graduating-valve 14, and is actuated by a piston 15 controlled by train-pipe air through a passage 18. The valve chamber communicates by a passage 19 with one side of a piston 21, the other side of which is open to reservoir pressure through a port 22. The piston 21 controls a valve 20, and the spindle of the valve abuts against a lever 24 keyed to the shaft 23, while a second lever 25 is keyed to the shaft outside the valve casing and is operated by the spindle of a piston 26. The right-hand side of the piston 26 is open to atmosphere, while the left-hand side communicates through a passage 28 with a small port 32 in the main valve seat, which is connected by a restricted passage 29', Fig. 4, with the brake-cylinder port 16. In the position shown in Fig. 3, the brake-cylinder port 16 is open to the exhaust port 17 through a port 31 in the main valve, a cavity 33 in the graduating-valve, and a port 30. In operation, the train-pipe pressure is reduced and the piston 15 moves to the left, first moving the graduating- valve 14 to close the communication between the brake cylinder and the exhaust port 17, and then moving the main valve 13<1> until the ports 31<1>, 32<1> register with the ports 16, 32 leading to the brake cylinder and the passage 28 respectively. This causes a reduction of pressure in the valve chamber and on the right-hand side of the piston 21, so that the latter is moved by the reservoir pressure to admit air from the reservoir to the brake cylinder through the valve 20, passage 19, and ports 31<1>, 16. As soon as the pressure in the main valve chamber together with the pressure on the piston 26 exceeds the reservoir pressure exerted on the left-hand side of the piston 21, the valve 20 is closed. A further small flow of air to the brake cylinder equalizes the pressure on the valve piston 15, and the graduating-valve 14 is moved to lap position. An increase of brake-cylinder pressure can be obtained by further reductions in train-pipe pressure, and the brake-cylinder pressure obtained by a given reduction in train-pipe pressure depends on the relative areas of the pistons 21, 26. To release the brakes partly, the train-pipe pressure is slightly increased to move the valve into release position, when the brake-cylinder pressure falls, consequently reducing the pressure on the left-hand side of the piston 26. The pressures on the sides of the piston 21 are then unbalanced, and the valve 20 opens to admit air into the valve chamber and return the piston and graduating valve to lap position and prevent further reduction of brake-cylinder pressure. A reservoir 34, Fig. 1, is connected by a pipe 35 to the valve chamber so that the leakage of air past the piston is prevented from affecting the movement of the main valve in response to changes in train-pipe pressure.