Beaver Inflating Valve
Date of manufacture:
The Beaver valve was originally developed for the Beaver ventilator, a mechanically driven bellows ventilator. It was subsequently supplied with the BOC Cyclator ventilator. The design of the valve would permit the patient to inhale from atmosphere through the exhaust valve were it not for an additional unidirectional neoprene mushroom exhaust valve.
When gas is being delivered from the ventilator via the inspiratory port, it causes pressure to rise in the large neoprene diaphragm. This impinges upon the seating, before the central mushroom one-way valve opens and delivers the gas to the patient. At the end of the inspiratory phase, the large diaphragm falls back to it's original position permitting the patient to exhale. The valve disassembles for cleaning and sterilisation. The valve was notorious for vibrating in use, librating a vulgar sound at the onset of each breath.
Macintosh Mushin & Epstein 'Physics for the Anaesthetist', 3rd Edn. 1963, Blackwell