Patent GB-796338-A (GB)
Title: Open circuit respiratory apparatus
IPC: A62B9/02
Filed: 1955-04-04
Abstract: 796,338. Respiratory apparatus. SPIROTECHNIQUE. April 4, 1955 [April 7, 1954; June 11, 1954], No. 9803/55. Class 81 (2). [Also in Group XXIX] Open circuit respiratory apparatus comprises a regulator having an air delivery valve controlled by a diaphragm exposed on one side to the surrounding medium, the diaphragm being influenced by a variable action device, which applies a decreasing thrust as the diaphragm moves away from a position in which the air delivery valve is opened, and means combined with the variable action device holding an exhaust valve closed when the delivery valve is open. A diaphragm 3 is clamped between portions 1, 2 of a casing to form an inhalation chamber 9 and a chamber open to the surrounding atmosphere. A cylinder of compressed gas is connected to a member 5, the gas passing through a first regulator comprising a valve 6 controlled by a diaphragm- 7 which is subjected to the thrust of a spring 8 and the pressure within the inhalation chamber 9, the latter being connected with a mouthpiece through a pipe 10. In the chamber open to the surrounding atmosphere is located a " duck bill " type exhalation duct 11 which is also connected with the mouthpiece. The exhalation duct 11 is opened and closed by a plate 13 the movement of which is limited by ends 12a of a yoke 12 fixed to portion 2 of the casing. The plate 13 is attached by a clip 18 to the centres of a blade spring 14 and a bowspring 15, the ends of the latter being held by ends 17 of a stirrup 16 attached to the diaphragm 3. When the user inhales, diaphragm 3 moves upwardly and, as the clip 18 remains stationary, the curvature of the spring 15 reverses and pushes against the clip 18 with an increased thrust. When this thrust is sufficient to overcome the thrust applied by the blade spring 14 holding the plate 13 so that the exhalation duct 11 is open, the plate 13 is pressed downwardly to close the exhalation duct 11. Movement of diaphragm 3 at the beginning of an inhalation opens the valve flap 4 so that valve 6 opens under the thrust of the spring 8 and compressed gas enters the inhalation chamber 9. At the beginning of an expiration, the slight increase of pressure forces the diaphragm 3 towards the plate 13, the valve flap 4 closes and the curvature of the spring 15 decreases so that its thrust decreases. This enables the blade spring 14 to lift the plate 13 so that the exhalation duct 11 is opened. The springs 14, 15 may be in the form of single elastic blades or elastic wires shaped into loops and lying in one plane when free. In a modification, Fig. 6, a supply of compressed gas is connected to a boss 5 and when a needle valve 4 is open gas flows through passages 22, 27 to a pipe 10 leading to the mouthpiece. The needle valve 4 is operated by levers 23 which contact parts 26 secured to the diaphragm 3, a spring 24 biasing the levers 23 so that they tend to close the needle valve 4. The diaphragm 3 divides the casing into two chambers the lower one 9 of which receives expired air through a duct 28. This causes the diaphragm 3 to move into the upper chamber so that the levers 23 close the needle valve 4. A rigid disc 29 forming the centre of the diaphragm 3 is provided with holes 30 normally closed by an expiration flap 11. A plate 31 above the expiration flap 11 is urged by springs 34 away from the expiration flap but movement is limited by a flange 33 of a pin 32 attached to the rigid disc 29. A looped wire spring 15 is held cambered between grooves 17 in a stirrup in the upper chamber which is open to the surrounding atmosphere. A knob 35 on the plate 31 is secured between adjacent loops of the spring 15. As the diaphragm 3 is moved into the upper chamber, the camber of the spring 15 is reversed so that the plate 31 is lifted from the expiration flap 11 which rises to allow the escape of expired air. On beginning an inhalation the pressure in the lower chamber 9 is reduced so that the diaphragm 3 moves into it, the ends of levers 23 moving with it so that the needle valve 4 is opened. The plate 31 moves with the diaphragm 3 so that the camber of the spring 15 is again reversed and the thrust applied by the spring 15 to the plate 31 is increased to cause the plate 31 to be pressed firmly against the expiration flap 11 keeping it closed.