See the attached Application Note "Spinesstic 22 Deadweight Gauge Fluid" for information on what fluid to use instead of the discontinued Spinesstic 22 fluid. Spinesstic 22 has also been referred to by these part numbers 55-500, PA9152 or DW6293. For reference, a MSDS is also at the end of this file.
In summary;
For models 2400, 2450, 2451, 2452, 2453, 2480, 2481, 2492 or 5000 piston gauges (also called dead weight testers), ST-55 oil is recommended. ST-55 oil mixes well with Spinesstic 22 and no seal changes are necessary.
For model 2485 piston gauges:
Sebacate (DOS) oil is recommended but does not mix well with Spinesstic 22 so the Spinesstic 22 must be fully removed and the seals must be replaced.
ST-55 oil can be used but the piston drop rate will be very slow due to the higher viscosity (almost double) of ST-55 compared to Spinesstic or Sebacate.
To maintain the lowest uncertainty, it is recommended to calibrate the 2485 piston/cylinder operating in the new fluid. Until the assembly can be calibrated in the new operating fluid, it can operate in either Sebacate or ST-55 using the existing calibration report. An additional 5 ppm uncertainty should be added to the piston/cylinder to account for the different operating fluid.
Here are part numbers, descriptions and links to the MSDS for each fluid.
Part Number: 3905893
Description: ST-55 Operating Fluid (Oil), Quart
MSDS and other information: ST-55 Information
Part Number: 3069043
Description: FLUID, SEBACATE, 1 QT
Part Number: 3069551
Description: FLUID, SEBACATE, 1 GAL
MSDS and other information: Sebacate Information