Precision differential pressure gauge - esp for aircraft fuel storage, has two-stage spring giving high accuracy at low pressure

摘要

A precision differential pressure gauge, for pressure and flow measurements of all types esp. for filter plants, water separators (for aircraft fuel) and/or pressure resistance measurements, comprises a glass piston suspended in a glass cylinder by a "duo" tension spring constituted of a weak and a strong spring in series with an abutment to limit the travel of the weak spring. The glasses of the piston and cylinder possess the same coefficient of thermal expansion. The graduation marks of the scale are 25 mm long and 0.5 mm wide to give no-parallelex reading along an imaginary line to the axis of the piston. The whole unit can be pivoted upside down, to permit removal of air from the bottom chamber. Each element of the filtration and water separation plant is connected through a pipe to a coordinator and the precision pressure gauge. Readings to plus-or-minus 0.05% of the differential pressure at 20 degrees C are obtained. The weak spring provides the high accuracy in the low-pressure range.