Update on Airflow System

New information gained through discussion with Performance Diver Technician: Allan Driscoll:

26/07/11

Demand valve systems work with compressed air supplies and can offer effortless breathing capability. Generally speaking, the larger the rubber diaphragm - the gentler the breathing work is.

The more energy demanding part of breathing through a circuit is the expiration phase - due to the fact that there is no force assisting you in moving the air. Where as, inspiring oxygen through a demand based supply is much easier due to the fact that the air is compressed so the resistance is less in between the point that the air is released - and your lungs.

The further the valve is positioned away from the mask - the more breathing resistance there will be due the fact that the distance to travel increases as well as the diameter of tube potentially becomes narrower. 

There may not need to be a demand based release mechanism as the air expired can exit through a one way valve provided there is as little resistance as possible.

There will only be a requirement for a mechanical valve if the expiratory limb is acting under vacuum.