The P3100/P3200 deadweight tester user manual refers to ST-55 fluid as "Shell Spindle Oil 22, our reference 55-655." We more commonly refer to it as ST-55 oil. Historically it has also been called Tellus 22, Morlina S2 or EL 22 or Fluid 22.
Part Number Description
3905893 ST-55 Operating Fluid (Oil), Quart
MSDS sheet is here,
EL DWT Fluid-22 (ST-55, 55-655, PA9152, DW6293)
Sample certificate of analysis link is below that shows shelf life of 4-years. ST-55 is almost always used with liquid deadweight testers, especially current models. Density is 879 kg/m3. Viscosity is 55 cSt at 20C, 22 cSt at 40C.
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