Oxygen Delivery Systems

| August 10, 2020 | By: Severe VFR
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An aircraft oxygen system consists of three components:

  1. A storage system
  2. A delivery system
  3. A mask or nasal cannula

This article aims to discuss the different types of delivery systems that can be installed and used on a variety of aircraft. 

Three types of oxygen delivery systems exist:

  1. Continuous Flow
  2. Diluter Demand
  3. Pressure Demand

Continuous Flow Delivery Systems

Continuous flow delivery systems offer a constant stream of oxygen from the oxygen storage container to the user's oxygen mask. 

Continuous flow devices are very economical and do not require complicated masks and regulators to function. 

However, continuous flow delivery systems continue to expel stored oxygen, whether the user is exhaling, inhaling, or pausing between breaths. This causes around 50% of the stored oxygen to be wasted and makes continuous flow delivery systems incredibly wasteful. 

Continuous flow delivery systems are typically used for aircraft flying at and below 28,000ft. 

Pros to Continuous Flow Delivery Systems:

  • Cheap To Operate
  • Does not require complicated masks or regulators to operate

Cons to Continous Flow Delivery Systems:

  • Extremely wasteful
  • Limited to altitudes below 28,000ft

Diluter Demand Delivery Systems

Diluter demand delivery systems compensate for the continuous flow system by supplying oxygen to the user only when it is "demanded" (During inhalation). 

Diluter demand delivery systems are designed to provide oxygen when the user inhales and stops oxygen flow when the user either pauses between breaths and or exhales. This allows oxygen to be conserved and last longer. 

Diluter demand delivery systems also dilute or mix stored oxygen with internal cabin air to give the user the proper oxygen percentage depending on the altitude of the aircraft. This mixing of air conserves stored oxygen and increases the length of time stored oxygen will last.

Diluter demand systems are typically used at altitudes up to 40,000ft. 

Diluter demand delivery systems do have the drawback of being more intricate and expensive than a continuous flow delivery system. 

Pros To Diluter Demand Delivery Systems

  • Conserves oxygen
  • Longer useful times for the same amount of oxygen
  • Can be used at altitudes up to 40,000ft

Cons To Diluter Demand Delivery Systems

  • More costly and complicated than continuous-flow devices

Pressure Demand Delivery Systems

Pressure demand delivery systems are typically only found on military aircraft and are designed to provide oxygen under positive pressure. 

This positive pressure forces oxygen into the lungs and slightly over inflates the lungs, allowing the lungs to be at a lower pressure altitude internally.

This system allows users to fly at altitudes above 40,000ft. At these altitudes, 100% oxygen without positive pressure will not be sufficient in giving oxygen to the user. 

Pressure demand delivery systems are the most expensive type of delivery system and are incredibly complicated in their design. 

Pros To Pressure Demand Delivery Systems

  • Allow the user to fly at altitudes above 40,000ft

Cons To Pressure Demand Delivery Systems

  • Requires a different method of breathing to compensate for the over-inflation of the user's lungs. 
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