Pressure – The Inner Working of the Basic Pressure Gauge

Everyday here at EXAIR we talk about pressure, specifically compressed air pressure. The other day I was looking up our model 9011, 1/4″ NPT Pressure Gauge , and it got me to wondering just how does this small piece of industrial equipment work. The best way to find out is to tear it apart.

9011_exair

Most mechanical gauges utilize a Bourdon-tube. The Bourdon-tube was invented in 1849 by a French watchmaker, Eugéne Bourdon.  The movable end of the Bourdon-tube is connected via a pivot pin/link to the lever.  The lever is an extension of the sector gear, and movement of the lever results in rotation of the sector gear. The sector gear meshes with a spur gear (not visible) on the indicator needle axle which passes through the gauge face and holds the indicator needle.  Lastly, there is a small hair spring in place to put tension on the gear system to eliminate gear lash and hysteresis.

When the pressure inside the Bourdon-tube increases, the Bourdon-tube will straighten. The amount of straightening that occurs is proportional to the pressure inside the tube. As the tube straightens, the movement engages the link, lever and gear system that results in the indicator needle sweeping across the gauge.

Pressure Gauge Top

The video below shows the application of air pressure to the Bourdon-tube and how it straightens, resulting in movement of the link/lever system, and rotation of the sector gear –  resulting in the needle movement.

If you need a pressure gauge or any of the EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

Send me an email
Find us on the Web 
Like us on Facebook
Twitter: @EXAIR_BB

The Evolution of the Nozzle

In the beginning, when hearing and energy conservation were not a consideration, simple open pipes were used for blow off operations. These are a waste of compressed air, dangerously loud, and potentially injurious. Federal regulations have since been implemented requiring hearing protection from exposure  to sound levels 90 dBA over a period of  8 hours or greater. It also mandates that if an orifice be dead ended against the skin it would not exhibit more than 30 psi.

safety nozzle

Safety Nozzle

Thirty years ago, EXAIR got its start making a more efficient nozzle that was O.S.H.A. compliant. The design sheltered the main air orifice down in a milled groove. The secondary orifice is an annular opening. This provides two functions. By chance if someone could find a way to block the main orifice, there is a secondary path for air to flow. The annular orifice also develops a tube of air surrounding the high velocity main air flow. This interaction deadens the sound level as well as creating a vacuum to draw in surrounding air.

Air Jet

air jet

The next step in the evolution is an air jet which utilizes the coanda effect which is the phenomenon where high velocity air will adhere to a surface. Compressed air is injected through an annular orifice at sonic velocity. The injected air is directed toward the output and creates a vacuum on the opposite end. This vacuum pulls in large volumes of free air and results in a larger volume of air on to the target. If one end or the other is blocked, flow simply reverses at well below OSHA dead ended pressure requirements.

Air Amplifier

air ampSimilar in design concept but in larger configurations is the air amplifier.  They move massive amounts of air which makes them an ideal solution for cooling, ventilating, and for blow off. Two styles were developed. An adjustable style were the annular orifice can manually be adjusted to control air flow and force. The second design has a fixed flow where the annular orifice is established with a patented shim.

Super Air Nozzle

nozzle

The more recent improvement on the safety nozzle is the Super Air Nozzle. The design concept here is to embed the orifices between fins around the perimeter of the nozzle. This prevents blockage by providing a path fore and aft for air to escape and remain below the OSHA dead end pressure threshold.  The high velocity air also creates a low pressure area drawing in up to 25 times in volume of surrounding ambient air than the volume of compressed air consumed. Sound levels are also greatly reduced.

EXAIR is not done exploring new and improved compressed air products. Product design is customer driven so we welcome your feedback.

Joe Panfalone
Application Engineer
Phone (513) 671-3322
Fax (513) 671-3363
Web: http://www.exair.com
Twitter: http://www.twitter.com/exair_jp
Facebook: http://www.facebook.com/exair