In Piston Type DP gauges, differential pressure is sensed by the movement of a precisely ground floating piston/magnet in a precision bore against a calibrated spring. Any variation in pressure on either side of the piston/magnet will cause the magnet to move proportionally to the change in differential pressure. A rotary pointer magnet located close to the internal magnet, but outside the pressure housing, follows the movement of the piston magnet and indicates differential pressure on the dial.

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.

CMC provides process instrumentation accessories from Mid-West Instrument such as Pulsation Dampeners, Pressure Limiting Valves and Manifold Valves. Mid-West Model 150 Pulsation Dampener is the most advanced pulsation dampener with fine dampening adjustments to protect both low and high displacement devices. Mid-West Model 200 Pressure Limiting Valve has a pressure limiting valve to prevent over-pressurization, automatic shutoff features, three adjustable range springs, and more. Mid-West Manifolds are rated at 6000 PSIG and 240°F, standard connections, dust cap shields, leak-free operation design, and much more.