Measuring and testing – Fluid pressure gauge – Bourdon
Reexamination Certificate
1995-12-13
2001-04-17
Oen, William (Department: 2855)
Measuring and testing
Fluid pressure gauge
Bourdon
C073S732000, C073S738000
Reexamination Certificate
active
06216541
ABSTRACT:
FIELD OF THE INVENTION
The field of art to which the invention pertains comprises pressure gauges affording controlled release from an encountered overpressure within the gauge.
BACKGROUND OF THE INVENTION
Pressure gauges are widely utilized in a myriad of different environments for commercial and industrial applications where measuring and indication of fluid pressure values is required. Depending on the instrument, values of pressure can be displayed in either digital or analog form. The primary sensing element of the gauge typically comprises a Bourdon tube having a free end that incurs a predictable displacement in response to pressure changes to which it is exposed. Typically, tube displacement is translated via a movement or amplifier to a rotatable pointer that is displaced opposite a dial of calibrated pressure values.
It can be appreciated that if and when an overpressure is encountered within the Bourdon tube it could, if of sufficient magnitude, cause the Bourdon tube to burst with the potential for exploding and throwing the case and/or lens. Needless to say, explosions of this type can prove hazardous, particularly to any bystander in the vicinity of the gauge.
A current standard of Underwriter's Laboratories, Inc., UL252A relates to “Compressed Gas Regulator Accessories”. The standard establishes the requirement that all components of a compressed gas regulator assembly including the pressure gauge operate at a selected maximum pressure of between 30-300 psig. Each gauge, whether of 30 psi max or 300 psi max. must be capable of withstanding a pressure five times its maximum operating pressure. At or above the five times multiple, the accessory shall either retain or release the pressure without rupture or throwing of parts. Burst pressures for a Bourdon tube can typically vary from about 1100 psi for a 30 psi max. gauge to 5,000 psi for a 300 psi max. gauge.
Various approaches for compliance with the above U.L. standard have included a perforator within the tube that punctures a hole in the tube in the course of deformation. Another approach has been to utilize conventional rear venting of the case to supposedly prevent injury in the vicinity of the gauge.
While operative, none of the above have been found sufficiently practical for an inexpensive pressure gauge and despite reccognition thereof, a ready solution has not heretofore been known.
OBJECTS OF THE INVENTION
It is an object of the invention to provide a novel Bourdon tube construction that per se enables the pressure gauge to operate in compliance with the requirements of UL252A.
It is a further object of the invention to effect the previous object with an economical construction affording a controlled and localized fracture of the Bourdon tube at a preselected location while continuing gas flow to within the tube is restricted.
It is a still further object of the invention to effect the previous objects with relatively inexpensive structural features for obtaining the sought-after result of a slow release to within the cavity of the surrounding case/lens.
SUMMARY OF THE INVENTION
This invention relates to pressure gauge apparatus for indicating values of gas pressure to which the gauge is to be exposed. More specifically, the invention relates to a pressure gauge having a construction complying with the requirements of UL252A in being able to effect relief on encountering a predetermined value of overpressure without exploding or throwing of gauge parts.
For achieving the foregoing, the Bourdon tube in the pressure gauge hereof is generally constructed and secured to the gauge socket using relatively high pressure welds or solders of a strength exceeding the burst strength of the tube walls. At a selected location on the tube wall, that in a preferred embodiment comprises a connection between the crimped free end tip of the Bourdon tube to an input channel bracket of the amplifier, there is provided a specially formulated selected solder for both sealing and securing the tip to the amplifier. The solder selected is characterized by the capability to fracture at relatively low levels of pressure above the overpressure limits imposed by the U.L. standard. With the tube tip located in the channel bracket of the amplifier, the bracket prevents the solder fracture from enlarging. At the same time the fracture occurs at a pressure value significantly below the burst pressure of the tube walls so as to enable the remainder of the tube to be sustained. Operative in conjunction therewith is a throttle plug located in the socket inlet to the Bourdon tube that functions to restrict post-fracture input flow to a safe level.
By virtue of the above, tube rupture and/or an enlarged rupture at the fracture site is avoided enabling the escaping gas to flow through the fracture into the case cavity from which it is ultimately dissipated. Being that the pressure of ongoing flow is sufficiently restricted, the case/lens envelope can readily contain an overpressure spike without throwing parts and thereby avoid the potential of injury as might otherwise be associated therewith. As a consequence, a relatively simple and inexpensive solution in compliance with UL252A is achieved.
The above noted features and advantages of the invention as well as other superior aspects thereof will be further appreciated by those skilled in the art upon reading the detailed description that follows in conjunction with the drawings.
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MIL-ST-454F, Requirement 5, “Soldering”, Jun. 30, 1979.
Dresser Industries Inc.
Oen William
Rubin Daniel
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