GB992402A - Improvements in or relating to safety devices for rail vehicles - Google Patents

Abstract

992,402. Fluid-pressure brakes. KNORR-BREMSE G.m.b.H. Sept. 13, 1961 [Sept. 14, 1960], No. 32880/61. Heading F2F. A deadman's device for rail vehicles comprises a vigilance key which is to be actuated by the driver of the vehicle but is to be released for a short time within successive, specified intervals, the key operating a valve which in one position causes air to be supplied slowly to a first timing container and rapidly to a second timing container, and in its other position discharges air rapidly from the first container and slowly from the second container, warning and/or braking apparatus being operated by the pressure in the first container if it exceeds a predetermined amount, and by the pressure in the second container if it falls below a predetermined pressure limit. As shown, a compressedair braking system includes a feed line 7, a control line 5, and a brake cylinder 39 supplied by a line 41 which receives compressed air from the feed line 7 via a conventional triple valve (not shown) operated by a reduction of pressure in the line 5. A driver's regulator valve 3 is provided for controlling the pressure in line 5. The deadman's device comprises a key 17 which when depressed causes air from the feed line 7 to pass via lines 21 and 33 to a first timing container 53 and via lines 21 and 57 to a second timing container 63, the feed to container 53 being slow since non-return valve 51 is arranged to cause the air to pass through construction 49 while the feed to container 63 is rapid since non- return valve 61 is arranged to by-pass constriction 59. On release of the key line 21 is vented to atmosphere so that container 53 discharges rapidly via non-return valve 51 and container 63 discharges slowly via constriction 59. Relay valve 27 normally maintains lines 21 and 33 in communication. Provided the key is depressed and released within predetermined time limits the pressure in container 53 never rises above one pre-set value and that in container 63 never falls below another pre-set value. If the pressure in container 53 rises above the pre-set value owing to failure of the driver to release the key 17 the pressure, communicated via double non-return valve 55 and normally open relay valve 77 to a control line 81, becomes sufficiently high to operate control pistons 91, 93 of relay valves 1, 11 which respectively shut off the connection between the feed pipe and the regulator valve 3 and cause air to be fed to a warning whistle 13. If the warning whistle is unheeded, after a further short period of time the continued rise in pressure in line 81 operates control pistons 85, 87 of relay valves 79, 89 which respectively connect line 81 to the feed pipe, so holding the relay valve 89 actuated, and vent the control pipe 5 to atmosphere. This causes an emergency application of the brakes. If, instead, the pressure in container 63 falls below the pre-set pressure, a relay valve 67 is operated to connect the feed pipe 7 to the control pipe 81 via the double non-return valve 55 so that the brakes in this case are applied immediately. After an emergency brake application by the device, the device must be re-set by moving a manually operated valve 86, which normally connects valve 79 to the line 81, to an alternative position wherein it vents the pipe 81 to atmosphere. To avoid the necessity for periodically releasing the key 17 during normal application and release of the brakes by the driver, relay valve 27 is arranged to vent the container 53 to atmosphere in either event by connections between each of two control chambers 35, 45 with the line 41, the former via non-return valve 37 and the latter via non-return valve 47. The chambers are interconnected via a restriction 43. During braking pressure in chamber 35 rises rapidly to cause venting of line 33 by movement of piston 29 to the right. Piston 29 returns after a delay necessary to equalize the pressures in chambers 35, 45 via constriction 43. Similarly, during release of the brakes, pressure in chamber 45 falls rapidly to again vent line 33. Relay valve 77 is operated to isolate the line 81 from the container 53 during a heavy or emergency application.