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A sensitive element of this device is a fluid pressure within the chamber. When balanced with a known weight this pressure used as a secondary standard for static calibration of pressure gages.
Calibrated pressure gage G is connected to the chamber when the valve V is closed. To fill the tester with a clean oils the plunger first moving to its most forward position. Withdraw the plunger slowly the oil is poured in through the opening for the piston.
When the valve V is open the known pressure exerted on the fluid by the piston is now transmitted to the calibrated gage. This pressure may be varied or by adding weights to the piston or by using different piston-
cylinder combinations of varying areas.
This is neither the area of the piston nor the area of the cylinder; while it is some effective area which depends on the clearance spacing and the viscosity of the oil. The smaller the clearance, the closer the effective area will approximate the cross-sectional area of the piston