GB1293479A - Medical ventilator including a fail-safe system - Google Patents

Abstract

1293479 Respiratory appliances PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 19 Aug 1971 38980/71 Heading A5T In a time cycled medical ventilator, driving gas is supplied from a source DG via an energised solenoid operated valve S1, to a port 1 of a pneumatically operated driving cylinder D.C.1 thus forcing the piston downwards to contract bellows B1 and B2 and expel therefrom a volume of respiratory gas. At the same time solenoid DS1 is de-energised to allow inspiratory valve I.V. to open so allowing the respiratory gas to pass at a rate determined via a flow rate controller F.R.C. to the patient via a non-return valve N.R.V.2 and gas is vented from the non-driving chamber of the driving cylinder to atmosphere via de-energised solenoid operated valve S2. When inspiration of respiratory gas is complete the solenoid of valve S.1 is de-energised and the solenoid of valve S.2 energised, so that driving gas is fed to port 2 of the driving cylinder, and vented to atmosphere via port 1 and valve S.1, the bellows being thus expanded to draw in respiratory gas via inlet RG and non-return valve N.R.V.1. Inspiratory valve I.V. is closed by energisation of solenoid D.S.1 and expiratory valve E.V. opened by de-energisation of solenoid D.S.2. A pressure relief valve comprises a valve member V.M., a valve seat V.S., and a weight W disposed on a lever arm L.A. pivoted at P. to limit the maximum pressure in the inspiration gas passage. A detecting means is arranged to open the relief valve to allow the patient to breathe if the driving gas supply fails, and comprises a variable capacity gas reservoir G.R. which is charged with driving gas via non-return valve N.R.V. 4 or N.R.V. 5, and vented to atmosphere via flow restrictor F.R. at a rate slower than the rate at which driving gas can be fed to the reservoir, so that if the driving gas supply fails the piston rod of the reservoir rises to engage the lever arm of the relief valve and opens it, but in normal operation the piston rod never reaches this height.