Date of manufacture:
Circa 1960. The bosun whistle was connected to the oxygen supply line of an anaesthetic machine. Pipeline oxygen at 4 bar was available so it had become practice to supply oxygen at that pressure to flow meters and high pressure devices such as some ventilators. The whistle mechanism is entirely pneumatic, being powered by the declining gas pressure once it reached the critical triggering pressure. As accidental pipeline disconnection would result in only a transient whistle, the Bosun was therefore also fitted with a battery powered alarm light that would continue illuminated until pressure was restored. This made it necessary to fit the alarm with an electrical on/off switch that somewhat negated its usefulness. The pneumatic system could also be switched off.
Oxygen failure alarm