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Anil More


The Do’s and Don’ts of Air Gauging

Get the most life and accuracy out of your air-gauging system

Published: Wednesday, February 15, 2023 - 13:02

It’s been decades since air gauging came into existence, and many changes and refinements have been made over the years. It has proved itself as a reliable and accurate method of gauging parts, particularly in cases of close tolerances and fine finishes. Its high accuracy, simplicity, and relatively low cost have made it the ideal solution for reliable high-volume, noncontact measurement right on the shop floor.

But every technology has its do’s and don’ts. If used correctly, air gauging is a boon—but if used improperly, it could spell disaster.

To get the most out of air gauging, consider the following do’s and don’ts:

The compressed air must be free from dust and other contaminants. The combination of dust, oil, and water is guaranteed to affect measurement accuracy or damage your equipment... or both.

The air pressure must be adequately high and constant, at least 1 to 1.5 bars (15 to 30 psi) higher than the regulated system pressure.

A good filter and a precise regulator are necessary to keep the compressed air clean and constant. Clean regulated air will result in faultless performance and provide longer life to your air-gauging system.

It’s good practice to switch off the air when it’s not in use, or use auto air-saving devices. Check and prevent leaks; compressed air is expensive, and if it’s continuously on, it will adversely affect the service life of the system.

If moisture in the compressed air remains on the inside of the jets in the air passage overnight, there’s a possibility of rust forming that will change the flow parameters and result in the gauge functioning incorrectly. Keep the gauges lightly oiled when not in use; this is true for all gauges and masters.

Periodic servicing helps to keep your system in good health (just like your car).

Air gauges shouldn’t be connected in-line with other pneumatic devices such as air guns or nozzles, pneumatic clamps or clutches, air motors, or any device where compressed air is used intermittently. This can cause a drop in pressure, even momentarily, leading to incorrect readings.

Install the air line so there’s a positive slope for liquids to flow to the lowest point, where they can be drained either manually or automatically. Underground air lines aren’t recommended. Always tap the connection required for the air gauge unit by looping over the pressure line and connecting the air gauge unit at right angles to the dropline.

Always try to use the air plug or air ring gauge with jets horizontal. This prevents the jets from being damaged accidentally. Any damage to the jet renders the gauge unusable.

While keeping the jets horizontal, it’s a good practice to rotate an airplug 180 degrees periodically, depending on the number of parts to be gauged, to subject the body to uniform wear. Even though air gauging is noncontact, the body—which acts as a guide and centralizes the jets—does come in contact with the part and hence is subject to wear.

The jet is a critical area on the air-gauge plug or ring. It’s responsible for metering the air, which directs it to fall on the gauging surface at a right angle to generate the right back pressure. Any damage to the jet will affect your measurement accuracy.

Pressure and the amount (volume) of airflow are critical to air gauging. If you look at the performance of air gauging in these terms, then your understanding of the entire gauging system will be sound. You need the right amount of air pressure and volume to do an accurate job.

Similarly, after impinging on the part, the air jet must flow out or escape to the atmosphere. Therefore, the air escape passage must remain clean for a free flow. Any obstruction will cause incorrect back pressure and an inaccurate measurement.

The air plug and air ring work in tandem with the air-gauge readout units. Hence, they must be compatible so the right amount of back pressure is developed to indicate correct linear readings. The holes inside the air-gauge unit circuit as well as those on the air plug or air ring are related. These must be checked and calibrated against a master jet that has been precisely manufactured. Master jet sizes are based on the system, e.g., Federal, CE, Johansson, PFL, or STOTZ.

Simple and yet highly accurate and reliable, the air gauge is an accurate tool if properly maintained. Hopefully the above suggestions will help.


About The Author

Anil More’s picture

Anil More

Anil More has 50 years of experience and knowledge in engineering metrology. He started his metrology journey with thread gauges at Horstmann India, and then with dial, air, and electronic gauges at Baker Mercer India. He is an ISO QMS-certified lead auditor who has worked in many industries big and small, traveled a lot, met many people, and seen many companies. Today he consults in the field of dimensional gauging, particularly in air gauging.