Patent GB-842874-A (GB)
Title: Improvements in or relating to automatic alarm and emergency devices in particular for breathing apparatus
IPC: A62B9/00
Filed: 1956-09-13
Abstract: 842,874 Respiratory appliances. BRONZAVIA S. A. Sept. 13, 1956 [Jan. 6, 1956], No. 27974/56. Class 81(2). Breathing apparatus comprising a chamber A which communicates with a breathing mask and is closed by a diaphragm B which opens a main oxygen supply valve 1 associated with a main jet 7, includes an auxiliary supply jet 8, through which oxygen is supplied to the chamber from the normal source by way of an emergency valve 36 controlled by means responsive to oxygen flow through the main supply valve, and alarm means actuated by the control means. The supply valve 1 of an aviation respiratory apparatus is opened on inhalation against a spring 4 by a lever 5 which bears against the diaphragm B. Oxygen then flows through supply pipes 2, 3 to an auxiliary chamber 6 and the main jet 7. Simultaneously oxygen flows through a first adjustable jet 22 to a second chamber 23 closed by a diaphragm 24. While the apparatus is operating normally, the pressure in the auxiliary chamber 6, during inhalation, is higher than that in the chamber A and is sufficient to hold open a discharge valve 26 against a spring 28. The discharge valve has a control chamber 30 connected with the auxiliary chamber 6 by a pipe 31. Alternatively the discharge valve is controlled by a lever (not shown) operated by the diaphragm of the second chamber 23. Oxygen reaching the second chamber normally flows through the discharge valve to the chamber A at each inhalation. In the event of failure of the supply valve or collapse of the user, the pressure in the auxiliary chamber 6 is no longer higher than that in the chamber A, the discharge valve closes and pressure builds up in the second chamber 23 at a rate dependent on the setting of the first adjustable jet 22. The diaphragm of the second chamber is displaced against a spring 19 and electrical contacts 27a are thus made to operate a sound or light alarm. The second chamber is connected through a second adjustable jet 33 with a control chamber 34 of the emergency valve 36. After a delay dependent on the setting of the second adjustable jet, the emergency valve opens, so that oxygen is supplied to the chamber A through pipes 2, 15, 38 & 9 and auxiliary jet 8. The normal supply pipes 2, 3 of the apparatus are connected by the pipe 15 with a third chamber 17 and a control chamber 14 of an auxiliary valve 10 which controls an auxiliary oxygen supply. The third chamber 17 is closed by a diaphragm 18 which is urged to decrease the volume of the third chamber by the spring 19. If the normal oxygen supply fails, pressure decreases in the third chamber 17 and the auxiliary valve control chamber 14, to make contacts 20a thus operating the alarm. Also, the auxiliary valve is opened to supply oxygen from the auxiliary supply to the chamber A through the auxiliary jet 8. The ratio of the surface areas of the diaphragms 18, 24, closing the second and third chambers, and the strength of the spring 19 are such that the alarm and emergency devices do not operate until a constant period of time has elapsed after the fault has arisen.