News on Pressure Testing Services

Primary vs Secondary Standards

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Pressure testing equipment calibration is important in ensuring that you collect accurate and reliable data through your work. While different devices and systems will require different calibration techniques, all calibration depends on either a primary or secondary (otherwise known as “transfer”) standard. But what, exactly, is the difference between primary vs secondary standards? Read more »


A Contemporary Version of the Bridgeman-Birch 30 Kilobar Apparatus

Posted by & filed under Technical Papers.


This paper briefly describes the basic Harwood kilobar apparatus, particularly its deviations from the original Bridgman model and the elaboration thereof by Birch for uses with gases at high temperature. Nearly all the physical measurements made by Bridgman at 12 kb can be made with this equipment at 30 kb, in some cases extending the temperature range.

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Hydraulically Driven Pumps

Posted by & filed under Technical Papers.


Excessive torque, side thrust, and friction make crank-driven pumps cumbersome and expensive at high pressures. But in hydraulically driven pumps, these effects are eliminated or minimized and higher pressures can be attained. Also, longer strokes are characteristic; therefore, rates of stress buildup are reduced in such areas as check valves and packings, which result in less maintenance and longer life. Without rotational inertia, controllability is increased which in turn increase safety.

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Piston Gauges as a Precise-Measuring Instrument

Posted by & filed under Technical Papers.


The errors which must be considered for accurate measurements of pressure with piston gauges are discussed. Harwood’s unique design of piston gauge which permits the operator to control the clearance between the piston and cylinder at any operating pressure is described. Instrument errors are thus substantially reduced, particularly those resulting from elastic distortion.  A check list of errors inherent to piston gauges is presented.

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