Measuring and testing – Specimen stress or strain – or testing by stress or strain... – Specified electrical sensor or system
Reexamination Certificate
2002-07-09
2004-06-22
Noori, Max (Department: 2855)
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
Specified electrical sensor or system
Reexamination Certificate
active
06752024
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to valve packing gland load sensing and monitoring devices, and more particularly to a sensor arrangement associated with a packing gland providing for monitoring of the valve packing gland compression load.
BACKGROUND OF THE INVENTION
Packing glands are used in many commercial, industrial and consumer applications to provide a conformable sealing member around a movable shaft or stem inserted through a cylindrically shaped cavity of larger diameter, generally called a stuffing box. A compressive load is typically created by an axial force applied by a packing gland or follower to conform the inner diameter of the packing to the outer diameter of the movable shaft or stem and the outer diameter of the packing to the inner diameter of the stuffing box so as to form a sealing relation therebetween. Proper product installation and loading of the packing is necessary for a lasting seal to be effected. Critical packing applications may contain liquids, gases or solids where leakage could lead to emissions with dramatic effect to safety or to the environment. Known applications include containing volatile organic compounds such as gasoline and carbolic acid, carcinogenic products such as benzene and toluene and poisonous products such as chlorine, phosgene, hydrogen cyanide and ammonia. Critical seal application likewise contain insecticide and defoliant products and suspected ozone depletion gases such as chlorinated hydrocarbons. The critical nature of the packing seal in these and many other applications is such that an improved method of installation and verification of packing integrity over time is paramount for safety, process control and as a deterrent to fugitive emissions and maintenance downtime.
Common causes of packing failure in equipment such as valve packing glands, pumps, compressors, probes, etc. can be from improper loading, over or under tightening of glands and misalignment of the shaft or stem. Too much compression can lead to excessive friction and premature wear, while too little compression can lead to premature leakage. Shaft or stem misalignment can lead to all the above problems. Packing integrity can change by over pressuring, surging, flashing, excessive temperature and combinations thereof by the material flowing through the valve packing gland. Such occurrences may cause over compression of the packing inside the stuffing box creating a leakage path even when springs are used to maintain compression. Changes in packing compression may also cause control valve packing glands to stick and slip resulting in unbalancing process control. Pumps, compressors, probes, mixers, etc. can also suffer from initial improper packing integrity and changes over time which result in unwanted emissions, safety issues, maintenance downtime and loss of production.
Therefore, it would be desirable to provide a packing sensor that would insure packing integrity and provide a correct, ongoing measure of the conditions known to be factors affecting packing performance with minimal variations from tolerances, environmental variations or other factors unrelated to packing failure mechanisms.
SUMMARY OF THE INVENTION
The present invention provides a valve packing gland load sensor and monitoring system that determines loading based upon a measurement of the capacitance of sensor capacitor that is associated with a packing gland or follower. The monitoring of valve packing gland compression load can be made during installation and/or sampling or continuous measurement of packing compression to provide early detection and corrective action prior to packing failure.
A thin flat disk-like capacitive load sensor of layered sandwich construction having a central opening and a circular outer periphery is installed above a packing follower or beneath the packing follower or packing gland. The load sensor has a thin first and second insulating outer layer between which an inner layer is secured. The inner layer is formed of dielectric material having a known dielectric constant which does not change when subjected to compression, a first face having at least one thin electrically conductive circular ring surrounding the central opening in coaxial radially spaced relation, and a second face having a thin electrically conductive circular ring surrounding the central opening in coaxial radially spaced relation. The inner and outer layers contain electrical conductors engaged with respective electrically conductive circular rings on the opposed faces that are adapted to be connected with an electrical measurement apparatus. As the inner layer is compressed, the spacing between the electrically conductive rings on the opposed faces is decreased such that compressive force on the packing can be measured as a function of the change in capacitance of the sensor. Proper compression of the packing can be achieved by monitoring during installation, and sampling or continuous measurement of packing compression provides early detection prior to packing failure to allow corrective action.
The valve packing gland load sensor capacitor and monitoring system of the present invention improves packing integrity and affords a correct and accurate ongoing measure of conditions known to be factors affecting packing performance with minimal variations from tolerances, environmental variations or other factors unrelated to packing failure mechanisms. The system can detect and monitor for proper packing load, ongoing process influences, and show the trends of these dynamics to allowing early detection of sealing and or process problems. The system is suitable for use in a wide range of environments and conditions in which the packing may be used, including large temperature and pressure variations and corrosive applications. The system is easily and quickly installed in conventional valve packing gland assemblies without special tools, and does not require modification of existing equipment.
REFERENCES:
patent: 3914715 (1975-10-01), Hubing et al.
patent: 4641107 (1987-02-01), Kalokitis
patent: 4914741 (1990-04-01), Brown et al.
patent: 5757146 (1998-05-01), Carder
patent: 5907102 (1999-05-01), Hilton et al.
patent: 5944970 (1999-08-01), Rosenblatt
Coffey E. Michael
Davie Neil R.
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