A Technical Data on Dead Weight Testers

An Introduction

Pressure is defined as force per unit area, where force is defined as mass multiplied by the acceleration acting on that mass:

P = F/A were F = M x g

Dead weight pressure testers use these principles to generate a very stable and accurate pressure, by use of a series of weights which can be loaded on to a piston unit which is housed inside a cylinder. In principle, the components of the above equations are as follows: A is the effective cross-sectional area of the piston unit M is the mass of the weights loaded on top of the piston unit in addition to the mass of the piston unit itself g is the gravitational acceleration acting on the piston and mass set.

The manufacture of piston-cylinders is all carried out on-site by highly skilled operatives, thus allowing total control over the tolerances in effective area on each and every DH-Budenberg piston-cylinder unit. To give some appreciation of the processes and quality control involved, a variation of one ten thousandth of a millimetre would cause a change in area of a 1/80th in² piston-cylinder unit by 63 ppm (parts per million).

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Technical Data on Dead Weight Testers - Overhaul & Recertification 

MAINTENANCE OF ACCURACY - The accuracy of a dead-weight tester depends primarily on the effective area of the Piston unit and on the weights applied to the Piston. The effective area of the Piston unit can be affected by wear of the unit. This is generally caused by contamination of the oil in the tester by foreign matter from instruments being calibrated, by water, or chemicals from instruments, or by rust or corrosion caused by contaminants. Weights are made of austenitic stainless steel which is entirely stable.

NEED FOR OVERHAUL AND RE-CERTIFICATION - We recommend that the tester be returned to us for overhaul and re-certification at any time if when used in accordance with instructions:

a) The Piston does not spin freely.

b) The rate of fall of the Piston is appreciably greater than when new and makes use of the tester difficult.

c) The weights are damaged or seriously corroded.

d) The tester cannot be made to operate satisfactorily due to wear or damage to pump piping or valves which cannot be rectified by the user.  

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