Apparatus and methods for dynamically pressure testing an article

The dynamic pressure tester includes a first cylinder and a first piston movable relative to the cylinder. The piston may have one or more weights applied thereto. The cylinder is vibrated by a shaker table and pressure pulses in the fluid are transmitted to a stationary housing and to a second piston in the housing. The opposite side of the piston contacts a corrosive or caustic fluid also in contact with the sensor face of an article being tested. The pressure pulses are transmitted by the second piston and corrosive fluid to the sensor face, enabling dynamic pressure testing in the corrosive fluid.

The present invention relates to apparatus and methods for dynamically pressure testing an article and particularly relates to testing apparatus and methods for simulating dynamic pressure on an article exposed to caustic or corrosive fluids in practical applications of the article.

BACKGROUND OF THE INVENTION

Dynamic pressure testing of articles, for example, pressure transducers for use in various applications is well known. Dynamic pressure testing is typically used to test the longevity of an article, e.g., a pressure transducer when subjected to a plurality of time dependent cycles. Many and different types of dynamic pressure testing apparatus have been utilized. For example, shock tube testing provides two sections of a tubing separated by a thin diaphragm. When a differential pressure is applied to the tube sections and the diaphragm ruptures, a resulting pressure shock occurs. Disadvantages of shock tube dynamic pressure testing include a complexity of and difficulty for setting up the test, is limited to one cycle only, cannot use liquid fluid media during testing and the shock wave raises the gas temperature. Shockless pressure step generators use a quick opening valve to generate dynamic pressure pulses. Generators of this type, however, are limited mechanically by the opening of the valve and are unable to reach high frequency pulses, i.e., cycles per second. Pulse generators typically employ a mass dropped onto a piston in contact with an incompressible fluid contained within a fixed volume. Generators of this type, however, are limited to single step response, i.e., one cycle. There are also shaker base systems which utilize a liquid filled tube mounted on an armature of a shaker to produce dynamic pressure. Shaker base systems, however, are generally cumbersome, require heavy duty shakers for large pressure displacements, and have their own governing maximum operating temperatures.

Pistonphones utilize a piston-in-cylinder to produce a sinusoidal pressure variation. While devices of this type are typically used with acoustic sensors such as microphones, pistonphones are limited to low frequencies and amplitudes. Finally, servo-valves generally use hydraulic systems to control dynamic components. Pressure is generated by an external pump and is dynamically controlled by applying a biased alternating signal to the servo-valve. This signal moves a mechanical member inside the servo-valve, in turn directing working fluid through various ports and controlling a shuttle valve. The end result is a dynamic pressure signal at the output.

Oftentimes, these dynamic pressure systems cannot meet amplitude and frequency requirements for many applications. Further, many articles are subjected to caustic or corrosive fluids in use. The combined stresses caused by the caustic or corrosive fluids as well as the pressure variations to which the article is subjected in use are stresses not typically accounted for in prior dynamic pressure testing systems. There is also a need in certain applications for a very substantial number of pressure cycles in a short period of time, e.g., one billion cycles in 40 days or less, to insure the adequacy of the dynamic pressure testing.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with an aspect of the present invention, there is provided a dynamic pressure testing apparatus and methods of dynamic pressure testing wherein the testing may be conducted at a significant range of frequencies, particularly high frequencies, with the article undergoing tests also being simultaneously subjected to caustic or corrosive fluids and the stresses caused thereby. In a preferred embodiment, a first cylinder with a piston slidable relative thereto are mounted on a shaker table or other suitable vibration generator whereby pressure pulses are generated in a first fluid in contact with the piston and cylinder. A second stationary housing or cylinder lies in fluid communication with the first fluid and includes a piston movable relative to the stationary housing or cylinder in response to the pressure pulses generated in the first fluid. The article undergoing testing lies in communication with a second fluid, e.g., a caustic or corrosive fluid also in communication with the second piston whereby the pressure pulses generated by the first fluid are transmitted via the second piston and second fluid to the article undergoing testing. With the article in contact with the caustic or corrosive second fluid and being subjected to the pressure pulses of the second fluid, the dynamic pressure testing may proceed at selected frequencies and amplitudes and temperatures limited only by the material of the testing apparatus. Moreover, by varying the mass of the first piston, e.g., by adding or removing mass to the first piston, the amplitudes and resonant frequencies of the generated pressure pulses can be varied as desired. For example, pressures can be generated with this test set-up in a range of 20–200 p.s.i. or higher with frequencies between about 100 Hz to about 400 Hz. A set-up of this type enables dynamic pressure testing using corrosive fluids over a large number of cycles in a limited time frame, e.g., one billion cycles in a matter of weeks and at desired resonant frequencies.

In a preferred embodiment according to the present invention, there is provided apparatus for dynamically pressure testing an article comprising a first cylinder containing a first fluid; a first piston in contact with the first fluid and movable within the first cylinder; a shaker table mounting the first cylinder and the first piston for vibrating the first cylinder and first piston and generating pressure pulses in the first fluid; a second fluid cylinder in communication with the first fluid, the second cylinder and a second piston movably carried by the second cylinder being mounted independently of the shaker table, the second piston in contact with the first fluid on one side thereof enabling the generated pressure pulses to vibrate the second piston; and a second fluid in the second cylinder in contact with the second piston on an opposite side thereof from the one side for receiving pressure pulses generated by the vibratory movement of the second piston and transmitting the second pressure pulses to an article undergoing dynamic pressure testing in contact with the second fluid.

In a preferred embodiment according to the present invention, there is provided apparatus for dynamically pressure testing an article comprising a first cylinder containing a first fluid; a first piston in contact with the first fluid and movable within the first cylinder; means for vibrating the first cylinder and the first piston to generate pressure pulses in the first fluid; a second fluid cylinder in communication with the first fluid, the second cylinder and a second piston movably carried by the second cylinder being mounted independently of the vibrating means, the second piston in contact with the first fluid on one side thereof, enabling the generated pressure pulses to vibrate the second piston; and a second fluid in the second cylinder in contact with the second piston on an opposite side thereof from the one side for receiving pressure pulses generated by the vibratory movement of the second piston and transmitting the second pressure pulses to an article undergoing dynamic pressure testing in contact with the second fluid.

In a preferred embodiment according to the present invention, there is provided apparatus

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, particularly toFIG. 1, there is schematically illustrated a dynamic pressure testing apparatus in accordance with a preferred aspect of the present invention and generally designated10. Apparatus10includes a fluid cylinder12and a piston14, the cylinder12and piston14being oriented vertically. As illustrated, piston14is sealed within the cylinder12by seals16and a fluid18is disposed in the cylinder12below piston14. The cylinder12is preferably disposed on a shaker table20. Shaker table20may comprise a conventional shaker table, e.g., a shaker table identified as M&B Dynamics Cal50, and preferably vibrates in a vertically oriented direction, enabling vibration of the cylinder12secured to the shaker table. It will be appreciated that any other suitable conventional apparatus for generating vibration may be used in lieu of a shaker table.

Apparatus10also includes a housing22carrying or forming a part of a second cylinder24. A second piston26is also carried by cylinder24. Piston26is sealed by seals28to the walls of cylinder24and lies in contact at one end with the fluid18. The opposite end of piston26lies in contact with a fluid30in a chamber32within cylinder24. Fluid30may be a caustic or corrosive fluid. As such, cylinder24and piston26and seals28are constructed from materials with the caustic fluid30media compatibility. At the opposite end of chamber32from piston26is the article34undergoing test. The article34is preferably secured to the housing22. An example of an article32is a pressure transducer for measuring pressures in a caustic environment.

One or more discrete masses or weights36may be disposed on the upper end, i.e., an exposed end of the piston14to weight the piston depending upon the amplitude and frequency of the pressure pulses desired to be generated. It will be appreciated that by operating the shaker table20in a vertical vibratory mode or at least to have a vertical vibratory component, the cylinder12and weighted piston14generate vibratory pressure pulses in fluid18. The vibratory pulses are transmitted to the fixed housing22via a semi-rigid connection38and serve to vibrate piston26within housing22. The vibration of piston26within cylinder22is transmitted through the caustic or corrosive fluid30to the sensing face of the article undergoing testing, e.g., a pressure transducer.

Referring now to drawingFIGS. 2–4, there is illustrated a specific preferred embodiment of the present invention. InFIG. 2, the cylinder12is illustrated mounted on the shaker table20. The piston14includes an active part, i.e., a lower stem36(FIGS. 3 and 4) carrying a pair of seals16, the stem and seals being received in the cylinder opening of cylinder12. The piston14also includes a pair of preferably diametrically opposite openings40which receive piston screws42. The screws42are received in the openings40and thread into female threaded openings44in cylinder12. Springs46(FIGS. 3 and 4) are also disposed in the piston14between flanges on their lower ends and the first weight36of a plurality of weights. The screws42and springs46serve to secure the piston14to the cylinder12, while, at the same time, allowing the piston to vibrate in response to the shaker table. The weights36may be secured on a stem45which projects upwardly from the piston14by means of a threaded nut46. The fluid18in the cylinder12also communicates via a semi-rigid line38with the housing22. The housing22includes a cylinder chamber which receives the piston26suitably sealed in the chamber by O-ring seals28. Additionally, the upper portion of housing22has female threads50for threaded engagement with a portion of the article34, e.g., the pressure transducer, for securing the transducers to the testing apparatus. It will be appreciated that the article34has a sensing face, not shown, which is exposed to the fluid in the chamber32.

The operation is similar to the operation previously described with respect to the diagrammatic illustration ofFIG. 1. The selected one or more of weights36serve in part to generate dynamic pressure in accordance with the equation p=ma/A where p is the pressure generated, m is the mass of the weights and piston, a is the acceleration response to the vibration and A is the surface area of piston14in contact with fluid18. The generated pressure pulses are transmitted to the piston26and hence to the second fluid30, e.g., the caustic or corrosive fluid. The transmitted pressure pulses are thus applied to the sensing face of the article32. In this preferred embodiment, it will be appreciated that the piston cylinder diameters and weights can be changed as desired to generate desired pressures. For example, a pressure range of 20–200 p.s.i. with the fixture being operated between 100 and 400 Hz, and preferably at about 300 Hz to obtain a resonant frequency, enables the testing apparatus to apply over one billion pressure cycles over a limited time period of two or three weeks to a pressure transducer32undergoing testing. More specifically, for example, pressure swings from 20–200 p.s.i. can be generated, with the system vibrating at resonance at 300 Hz, by utilizing 2 pounds-mass of weights and a piston area of 0.1 square inch and an acceleration due to the vibration of 10 g's. At 300 Hz, continuous operation, 1 billion cycles can be achieved in under 40 days. Thus, it will be appreciated that the testing apparatus is operable over a wide range of pressures, can be used at any required temperature subject only to temperature limitations of the materials of the testing apparatus. The testing apparatus may accommodate most fluid media capable of transmitting pressure waves and is particularly useful for testing articles which will be subjected to caustic or corrosive fluids and at a wide range of pressures and frequencies.