Giusca, C; Severn, I; Greenwood, J C (2007) The effect of hydraulic fluids on pressure balances. NPL Report. DEPC-EM 009

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Abstract

This work was initiated as a response to growing concerns about the effect of using different oils in Pressure Balances, which are used to realise the pressure scale both as national standards and as calibration instruments in the industry.
We report, for the first time, systematic errors in the effective area of a Pressure Balance that are directly attributable to the use of different oils as pressure transmitting fluid. To avoid the cancelling effects of the traditional cross-floating technique, an alternative technique is reported in which the measurements are made using two separate oils simultaneously. The influence of four lubricating oils on three nominal sizes of piston-cylinders assemblies, covering the pressure range 2.8 MPa to 200 MPa, has been investigated.
The change in effective area relative to operation with a sebacate oil was also found to be dependent on the pressure and therefore on gap size, however at this time we cannot make any quantitative predictions relating the size of the effect to the gap.
Although a difference related to the liquid viscosity (due to its contribution to the pressure distribution in the piston-cylinder inner space) was intuitively expected, the measurements instead appear to correlate more closely with the liquid density.

Item Type:	Report/Guide (NPL Report)
NPL Report No.:	DEPC-EM 009
Keywords:	oil pressure balance
Subjects:	Engineering Measurements Engineering Measurements > Mass, Force, Pressure
Last Modified:	02 Feb 2018 13:15
URI:	https://eprintspublications.npl.co.uk/id/eprint/3809