RESISTANCE, REVERSE FLOW AND OPENING PRESSURE OF UNIDIRECTIONAL VALVES

Based on a new preliminary standard of the 'Comite Europeen de Normali sation', the following unidirectional valves were tested with regard t o resistance, opening pressure, reverse flow and dislocation: the Drag er inspiratory and expiratory valves, the Engstrom inspiratory valve, the Ohmeda value, the Siemens Ventilator 710 inspiratory and expirator y valves, the Siemens Ventilator 900C unidirectional valve of the abso rber and the Megamed 700 inspiratory and expiratory values of the circ le system 219 (Megamed 700 CS 219). The following values fulfilled all Comite Europeen de Normalisation requirements: Drager inspiratory and expiratory valves, Siemens 900 absorber valve and Megamed 700 CS 219 inspiratory valve. The Siemens 710 valve and the Megamed 700 CS 219 ex piratory valve did not meet the requirements for flow resistance. The Ohmeda and Siemens 710 valves and the Engstrom inspiratory valve did n ot fulfil the Comite Europeen de Normalisation requirements for revers e flow. In addition, the Engstrom inspiratory valve did not comply wit h the dislocation test. The requirements for the opening pressure were met by all the valves tested. Valves with the disc in a horizontal po sition achieved better results than those with the disc in a vertical position. These measurements, showing the differences in the performan ce of various types of values confirm the feasibility of the standards proposal.