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 »
News on Pressure Testing Services
This technical paper describing the methods, concepts, and operation of a 150,000 PSI dynamic pressure calibrator was originally written in October of 1987. All tests were performed by the US Army Ballistic Research Lab at the Aberdeen Proving Ground in Maryland.
Abstract: A positive step pressure generator suitable for the dynamic calibration of ballistic pressure transducers is described. The device uses a hydraulic system to generate pressures up to 150,000 pounds per square inch and is capable of delivering pressure steps in one millisecond or less. Final pressure step values can be traced to conventional deadweight calibration figures with an accuracy of 0.2% by using a transfer standard (static reference gage). Among the uses for the device are examining transducer response characteristics to rapid positive pressure steps and comparing the relative response behavior of several transducers to a common pressure step. Read more »
Harwood Engineering has supplied pressurizing equipment for autofrettage service since its inception in 1948. Generally, the requirement has been for the autofrettage of large steel forgings. Recently, however, we have developed a system for the pressure testing and autofrettage of small parts, such as diesel nozzles and manifolds for diesel engines.
The system, as far as the pressure generation is concerned, is quite automated – once the pieces to be autofrettaged are connected to the output of the system, the operator presses “start” and the system will generate the necessary high pressure, hold it for a predetermined time, and release the pressure. Read more »
This paper briefly describes the basic Harwood 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.
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.
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.
A number of improvements in apparatus and technique have been made since the production of the prototype model of the controlled-clearance piston gage used by Johnson and Newhall in their 1953 determination of the freezing pressure of mercury at 0oC.