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Adjustable pressure-limiting valve

Flow control valve used in anaesthesiology From Wikipedia, the free encyclopedia

Adjustable pressure-limiting valve
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An adjustable pressure-limiting valve (commonly abbreviated to APL valve, and also referred to as an expiratory valve, relief valve or spill valve) is a type of flow control valve used in anaesthesiology as part of a breathing system. It allows excess fresh gas flow and exhaled gases to leave the system while preventing ambient air from entering.[1]

Thumb
The adjustable pressure-limiting valve on a General Electric Datex-Ohmeda Aisys anaesthetic machine, with pressure gradations shown in centimetres of water
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Mechanism

Such valves were first described by the American dentist Jay Heidbrink, who used a thin disc that was held in place by a spring.[2] The valve is adjustable and spring-loaded, allowing the opening pressure of the valve to be controlled by screwing the valve top which modifies the pressure on the spring.[1] A very light spring is used, so that at its minimum setting the valve can be opened by the patient's breathing alone using low pressures.[3] In contemporary APL valves, three orifices or "ports" are present: one for intake of gas, one for return of gas to the patient, and an exhaust port for waste gas which can be connected to a scavenging system.[1][4]

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References

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