The Nelson oxygen flow meters were the first products developed by Nelson Aircraft about 20 years ago. At that time the company was Ted Nelson Company. They were originally intended for high altitude use in sailplanes. Shortly after the introduction of the flow meters, many power pilots also indicated interest in the units. Over the years several versions of the flow meters have been produced. The A-1A, A-3, and A-4 series of flow meters have been very popular among pilots of all types of aircraft as well as other manufactures and distributors of aircraft oxygen equipment.

The Nelson flow meters meet FAA regulations (FAR 23.1449) to indicate oxygen flow. They replace the common red/green type of flow indicator which has been provided for in most factory built in and portable systems.

There are many reasons to use the Nelson flow meters. In most cases, the duration of the existing built-in or portable can be greatly increased. Using the A-3 or A-4 flow meters in most Cessna reciprocating engine aircraft produces remarkable duration increases. The Cessna built-in systems use a fixed flow rate oxygen system that will provide the proper oxygen flow for the service ceiling of the aircraft. Excess oxygen will be used at any altitude lower than the service ceiling. When the adjustable flow meters with Oxymizer® cannulas are used with the built in oxygen in Cessna's, the duration is increased up to 10 times at 10,000 ft. and a 3 times increase at 18,000 ft. can be expected. Nelson flow meters and Oxymizer®s used in typical Beechcraft, Mooney, and Piper built in Scott systems will also have increased oxygen altitude capability. Figure a 2 times increase at 18,000 ft. and a 3 times increase at 10,000 ft.

The Nelson flow meters and Oxymizer®s can be used with any portable oxygen system.

A major safety improvement will occur with the Nelson flow meters when they replace the common red/green flow indicators. The red/green indicators only tell the user that there is a flow of oxygen. They do not tell the user if there is a correct flow rate, only that something is happening. The Nelson flow meters show the actual flow rate. Many of the red/green indicators go from red to green at a flow rate much less than 10,000 ft.. If there were a malfunction in the oxygen system that causes a restriction in flow, one could be flying at 25,000 ft. indicating a green flow reading, but have an actual flow rate of less than 10,000 ft. That could cause serious problems for the pilot and passengers.

A medical advantage occurs with the use of the Nelson flow meters. At altitudes that oxygen is flowing more than needed, Cessna's in particular, the nose has a tendency to dry out quickly. Sometimes a headache can occur due to the dryness. The corrected flow rate for the altitude can prevent this dryness.

Of course there is an economic advantage for the use of the Nelson flow meters. Longer durations mean lower costs for oxygen refills. Actually the flow meters can pay for themselves in a short time, just by the savings of oxygen.

The longer durations caused by the use of the Nelson flow meters means one will not have to refill the oxygen cylinder(s) as often. Perhaps one would not have to worry about refilling at an unknown airport, if there is enough extra oxygen to be able to come back home and refill there.

Each person in the aircraft has one of the flow meters and can easily adjust the meters as necessary. The meters consist of a ball inside a tapered tube about 2 1/2 inches long. Along side of the tube is a scale(s) marked in altitude. At the base of the flow meter is a precision needle valve assembly that easily adjusts the flow of oxygen. To operate the flow meter, the user holds the unit approximately vertical, and then adjusts the needle valve to locate the floating ball next to the appropriate altitude scale. As the aircraft changes altitude, the flow rate is readjusted accordingly. After the setting is made, the flow meter can be placed in any position. The flow meter should be inspected for proper flow about 3-4 times an hour during cruising flight.

The A-3 flow meter is calibrated for use with the Oxymizer® cannula and provides the minimum flow rate possible. The Oxymizer® cannula collects oxygen wasted during the exhaling process of your breathing and accumulates the oxygen in a built in storage reservoir. At 18,000 ft. the savings are doubled and at 10,000 ft. the savings are tripled.

FAA regulations allow the use of cannulas to 18,000 ft. Above that altitude a face mask must be used. The A-4 flow meter is similar to the A-3, but it has two altitude scales. The scale on the left is for the Oxymizer® and is marked from 10,000 ft. to 18,000 ft.. This scale only goes about 1/4 the distance of the tapered tube and has a slightly higher flow rate for the Oxymizer®. This is to allow for a safety margin because of the shortened length of its altitude scale. The right hand scale is for face mask use and is calibrated from 10,000 ft. to 25,000 ft. This scale goes the full length of the tapered tube.

Typically, the A-3 is used for non-turbo aircraft. Most non-turbo aircraft cannot operate over 18,000 ft. which happens to be the limiting altitude for the Oxymizer® cannulas. The A-4 is recommended for turbo aircraft that operate up to 25,000 ft.. A combination of meters can also be used in turbo aircraft. A-3's are recommended for the rear passenger seats and A-4's for the front seats. Typically when flying with four people, turbo aircraft are not operated over 18,000 ft. or so. The A-3 can be used with a face mask by opening up the oxygen flow control needle valve wide open. The resultant flow would be the maximum capacity for the oxygen system. Typically a 25,000 ft. flow rate for a mask.

In a turbo aircraft the Oxymizer® and the A-4's left hand scale are used during flight operations below 18,000 ft. If the aircraft is flown above 18,000 ft., then the Oxymizer® is replaced with a face mask and the right hand higher flow rate scale is used. To accomplish this all one has to do is pull the flow meter output hose from the Oxymizer®, and push the hose onto the face mask. The is easily done in a few seconds. The reverse is done when descending below 18,000 ft..

Offered are two other specialty flow meters. The A-3M and A-1A. The A-3M is a non-adjustable unit for only monitoring oxygen Oxymizer® flow rates.

The A-3M flow indicator can be used with other aircraft oxygen systems to verify the actual variable or fixed flow rates. It can be used to replace the red/green flow indicators. The Scott MKII and Sky-Ox systems performance can be improved using the A-3M flow indicator. The A-3M will greatly improve the performance of these two systems since they only use a on-off oxygen flow indicator.

The A-1A is intended to be used only with a face mask or a standard cannula. It is calibrated only for the required oxygen flow for face masks. It is fully adjustable just like the A-4 flow meter. Pilots who have a microphone equipped mask can use an A-1A instead of an A-4. An A-3 is used with the Oxymizer® below 18,000 ft. and the A-1A is used with the microphone equipped mask.

To install the A-1A, A-3, or A-4 flow meters simply attach your existing hose connector (flow meters with connectors installed are available) to the input tubing attached to the flow meter. A clamp provided assures positive attachment. The clamp is necessary since there is a small amount pressure created between the connector and the input or needle valve control. Without the clamp, the hose could come off. The Oxymizer®, standard cannula, or face mask, is easily attached to the output tubing of the meter.

The A-3M flow meter does not come with any hoses and is simply put between the connector and the cannula or mask. The existing hose is cut in half and each half is attached to the A-3M meter's fittings.