Hydraulic Fluid
A specialized synthetic fluid transmits pressure from an external isolating diaphragm to an internal sensing element in harsh industrial environments. Process pressure transmitters utilize fluorosilicone fill oil due to its chemical inertness and low compressibility across broad temperature ranges. The fluid fills the internal capillary cavity under high vacuum to eliminate gas bubbles that would degrade dynamic frequency response.
Media compatibility requirements determine fluid selection when aggressive chemical vapors could permeate the primary isolating membrane.
Viscosity Index
Fluid density and fluid resistance shift with ambient temperature fluctuations. Lower temperatures increase oil viscosity, slowing response time and creating transient measurement lag during rapid pressure spikes. High temperatures reduce fluid density, altering zero offset stability in low-range pressure sensors.
Chemical Resistance
Fluorinated polymers resist degradation when exposed to aggressive solvents or hydrocarbon mixtures. Standard silicone fluids degrade or swell when exposed to aggressive media, whereas fluorosilicone fill oil maintains volume stability. Membrane pinholes allow minor fluid contact with process media without causing catastrophic reaction or fluid breakdown.
Outgassing Limit
Vacuum filling procedures require low vapor pressure fluids to avoid cavitation at elevated operational temperatures. Calibration labs verify fluid fill integrity by checking zero stability during vacuum exposure.
