Mid-West Instrument
Made in the USA
Tel: (586) 254-6500 · Fax: (586) 254-6509
6500 Dobry Dr., Sterling Heights, Michigan 48314
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Precision Bellows / Bourdon Differential Pressure Gauges & Switches - Models 105 / 106 109 Precision Bellows / Bourdon Differential Pressure Gauges & Switches - Models 105 / 106 109
Low ∆P Range 0-10" H2O to 0-400"
H2O (25 mbar-1 bar)
Models 105/106, 109

Product Features/Benefits

  • Dry Design, No Liquid Fill Required for Over-range Protection
  • Glass Reinforced Thermoplastic Gauge Front Is Standard
  • Weather Resistant & Corrosion Resistant Gauge Front
  • ± 1/2% or ± 1% Full Scale Accuracy
  • Six Inch Dial Standard
  • 5 Year Warranty
Low ∆P Range 0-10" H2O to 0-400"
H2O (25 mbar-1 bar)
∆P Range 0-15 PSID (0-1.0 bar) to
0-6000 PSID (0-400 bar)
Models 105 / 106 109
Models 105/106 and 109 gauges
are optionally available with one or
two switches for alarm and control.
The Model 105/106 bellows design provides a simple, compact, accurate, direct-acting, low range differential pressure indicator.

The major components of the Model 105/106 are a two-piece body, bellows sensing element and over-pressure assembly, a torque tube assembly, a range spring and the gauge front assembly.

The body halves provide the pressure containment function. They also clamp the sensing element and over-pressure assembly between the halves, isolating the high side and low side pressures of the system. The high side body half also provides a mount for the torque tube assembly and the gauge front assembly.

The sensing element is exposed to the differential pressure and deflects in response to the differential pressure. This assembly incorporates a bidirectional relief valve which provides over-pressure protection in both directions. When over-pressured from the high side, the valve is opened by a mechanical stop as the sensing element deflects to its maximum travel. When over-pressured from the low side, the spring-loaded valve opens when the differential pressure exceeds its maximum rating. The opening of the valve in either direction equalizes the pressure and protects the unit.

A range spring is provided to adjust the spring rate of the system to suit the various differential pressure ranges of the instrument.

The Model 109 encapsulated Bourdon tube design provides a simple, compact, and accurate differential pressure indicator.

The Model 109 is powered by a test quality Bourdon Tube Assembly. The assembly is encapsulated in a high pressure chamber that is fitted with a pressure connection to the inside of the Bourdon Tube and a second connection to the pressure chamber. The Model 109 indicates the difference between the pressure applied inside the Bourdon Tube and the pressure inside the chamber.

The pressure chamber for the assembly is small, close fitting and rugged. The volume displacement of the Bourdon Tube through the pressure range is near to zero (0.02 c.c.). The speed of response of the indicator to changes in differential pressure is instantaneous, even on low volume pressure systems. The low volume displacement is an important advantage for differential pressure leak detection, and when isolation diaphragms are required.

The Bourdon Tube Assembly is protected against over-range in either direction to the rated working pressure by a bi-directional relief valve. The output shaft of the gauge assembly is magnetically coupled through the solid wall of the pressure chamber to a sensitive jeweled pointer shaft in the dial housing outside the chamber. The magnetic coupling transmits the exact motion of the assembly to the pointer to give an accurate dial reading of the differential pressure.