Filling fluid

A pressure connection with a flush diaphragm has two diaphragms. The medium is in direct contact (flush) with only the first diaphragm, which then acts on a transmission fluid (the filling fluid) that relays pressure to the second diaphragm. The measured medium exerts a force on the outer surface of the first diaphragm. As the diaphragm flexes inward, it attempts to compress the filling fluid inside the instrument. This filling fluid is designed to resist compression, so the force is channeled directly to the second diaphragm. The entire operation of the diaphragm pressure sensor is based on Pascal's principle. This principle states that a pressure exerted on a fluid is transmitted without loss through the fluid in all directions.

The most commonly used filling fluids are silicone oils*#151;DC-200 or DC-704. However, DC-704 is not recommended for use with nitric or sulfuric acids. CTFE (Inert Fill) is ideal for chlorine or oxygen service. Syltherm 800 primarily is used for process temperatures from 450 to 600 degrees Fahrenheit. Neobee M-20 is suitable for sanitary applications because it meets FDA Regulation 21CFR172.856.