Continuous Flow Regulators

Continuous Flow Regulators

1) Manual Continuous Flow Regulator

A typical manually adjusted continuous flow oxygen regulator is shown in Figure 9.1. The gauge on the right shows the pressure of the oxygen in the system and indicates indirectly the amount of oxygen available. The gauge on the left is a flow indicator and is adjusted by the knob in the lower centre of the regulator. As the airplane ascends into the less dense air, the occupants need more oxygen, and with this type of regulator the user is able to adjust the flow to correspond with the altitude being flown, and the regulator will meter the correct amount of oxygen.

Automatic Continuous Flow Regulator

An automatic regulator, such as the one in Figure 9.2, has a barometric control valve that automat­ically adjusts the oxygen flow to correspond with the altitude being flown. The flight crew need only open the valve on the front of the regulator, and the correct amount of oxygen will be metered into the system for the altitude being flown.

Figure 9.2: Automatic continuous flow oxygen regulator.

b) Demand Regulators

The simple demand-type oxygen regulator, such as the one seen on the cylinder in Figure 9.3, meters oxygen to the user only during inhale. This type of regulator is far more economical of the oxygen than the continuous flow type, but there are regulators that are even more efficient.

Oxygen is almost always supplied to the crew of an aircraft by an efficient system that uses one of the demand-type regulators. Demand regulators allow a flow of oxygen only when the user is inhaling and shuts it off during exhale. There are several types of these regulators, as we will see

Figure 9.3: Portable oxygen system fitted with a demand regulator feeding oxygen to a full-face type mask.

Diluter Demand Regulators

The oxygen regulator used by the flight crews for most commercial jet aircraft are of the diluter demand type. In Figure 9.4 we have a very basic schematic of this type of regulator. When the supply lever is turned on, oxygen can flow from the supply into the regulator. There is a pressure reducer at the inlet of the regulator that decreases the pressure to a value that is usable by the regulator. The demand valve shuts off all flow of oxygen to the mask until the wearer inhales and decreases the pressure inside the regulator. This decreased pressure pulls the demand diaphragm over and opens the demand valve so oxygen can flow through the regulator to the mask.

A diluter demand regulator dilutes the oxygen supplied to the mask with air from the cabin. This air enters the regulator through the inlet air valve and passes around the air metering valve. At low altitude, the air inlet passage is open and the passage to the oxygen demand valve is restricted so the user gets mostly air from the cabin. As the aircraft goes up in altitude, the barometric control bellows expands and opens the oxygen passage while closing off the air passage. At an altitude of around 34,000 feet, the air passage is completely closed off, and every time the user inhales, pure oxygen is metered to the mask.

If there is ever smoke in the cabin, or if for any reason the user wants pure oxygen, the oxygen selector on the face of the regulator can be moved from the NORMAL position to the 100% position. This closes the outside air passage and opens a supplemental oxygen valve inside the regulator so pure oxygen can flow to the mask.

An additional safety feature is incorporated that bypasses the regulator. When the emergency lever is placed in the EMERGENCY position, the demand valve is held open and oxygen flows con­tinuously from the supply system to the mask as long as the supply lever is in the ON position.

Figure 9.4: A diluter demand regulator