Valve packing gland pressure sensing by capacitance measurement
First Claim
1. A system for determining the compressive loading of a packing gland providing a seal around an elongate member inserted through a stuffing box, the packing gland being compressed by a source of applied force, comprising:
- a load sensor for disposition between the packing gland and the source of applied force comprising;
a compressible inner layer having opposed generally flat faces on opposite sides and a central opening, said inner layer formed of dielectric material having a known dielectric constant;
an electrically conductive ring on a first one of the faces and surrounding the central opening;
an electrically conductive ring on the second, opposite face and surrounding the central opening;
a first outer layer of dielectric material having a central opening in registration with the central opening in the inner layer;
a second outer layer of dielectric material having a central opening in registration with the central opening in the inner layer; and
a pair of conductors coupled to the electrically conductive rings on the faces of the inner layer; and
a capacitance measuring instrument connectable to the load sensor conductors and producing a signal indicative of the measured capacitance between the electrically conductive rings as a function of the spacing between the rings; and
a display coupled to the capacitance-measuring instrument to receive the measured capacitance signal and provide a readout of the compressive loading on the packing gland.
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Accused Products
Abstract
A thin flat disk-like capacitive load sensor of layered sandwich construction having a central opening and a circular outer periphery for installation 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, 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 said 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. Follow-up sampling or continuous measurement of packing compression provides early detection prior to packing failure to allow corrective action.
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Citations
17 Claims
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1. A system for determining the compressive loading of a packing gland providing a seal around an elongate member inserted through a stuffing box, the packing gland being compressed by a source of applied force, comprising:
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a load sensor for disposition between the packing gland and the source of applied force comprising;
a compressible inner layer having opposed generally flat faces on opposite sides and a central opening, said inner layer formed of dielectric material having a known dielectric constant;
an electrically conductive ring on a first one of the faces and surrounding the central opening;
an electrically conductive ring on the second, opposite face and surrounding the central opening;
a first outer layer of dielectric material having a central opening in registration with the central opening in the inner layer;
a second outer layer of dielectric material having a central opening in registration with the central opening in the inner layer; and
a pair of conductors coupled to the electrically conductive rings on the faces of the inner layer; and
a capacitance measuring instrument connectable to the load sensor conductors and producing a signal indicative of the measured capacitance between the electrically conductive rings as a function of the spacing between the rings; and
a display coupled to the capacitance-measuring instrument to receive the measured capacitance signal and provide a readout of the compressive loading on the packing gland. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A compression load sensor for disposition between a packing gland providing a seal around an elongate member inserted through a stuffing box and a source of applied force compressing the packing gland, comprising:
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a compressible inner layer having opposed generally flat faces on opposite sides and a central opening, said inner layer formed of dielectric material having a known dielectric constant;
an electrically conductive ring on a first one of the faces and surrounding the central opening;
an electrically conductive ring on the second, opposite face and surrounding the central opening;
a first outer layer of dielectric material having a central opening in registration with the central opening in the inner layer;
a second outer layer of dielectric material having a central opening in registration with the central opening in the inner layer; and
a pair of conductors coupled to the electrically conductive rings on the faces of the inner layer.
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17. A system for determining the compressive loading of a packing gland providing a seal around an elongate member inserted through a stuffing box, the packing gland being compressed by a source of applied force, comprising:
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a load sensor for disposition between the packing gland and the source of applied force in the area of packing gland compression comprising a capacitor having;
a compressible inner layer having opposed generally flat faces on opposite sides and a central opening, said inner layer formed of a dielectric material having a known dielectric constant;
a first plate comprising an electrically conductive ring on a first one of the faces and surrounding the central opening;
a second plate comprising an electrically conductive surface on the second, opposite face;
a first outer layer of dielectric material having a central opening in registration with the central opening in the inner layer; and
a second outer layer of dielectric material having a central opening in registration with the central opening in the inner layer;
a reference sensor disposed outside the area of packing gland compression comprising a capacitor having;
a first plate comprising an electrically conductive ring on the first one of the faces of the inner layer of the load sensor, the ring being radially displaced from the electrically conductive ring on the first one of the faces of the inner layer of the load sensor; and
a second plate comprising the electrically conductive surface on the second, opposite face of the inner layer of the load sensor;
a first conductor coupled to the electrically conductive ring plate of the load sensor;
a second conductor coupled to the electrically conductive ring plate of the reference sensor;
a third conductor coupled to the electrically conductive surface plate on the second, opposite face of the inner layer;
a capacitance measuring instrument individually connectable to the load sensor and to the reference sensor, said capacitance measuring instrument producing an output indicative of the measured capacitance of the load sensor and of the measured capacitance of the reference sensor; and
a circuit coupled to the capacitance measuring instrument to receive the measurement output for the load sensor and the measurement output for the reference sensor, the circuit combining the outputs to produce corrected load sensor outputs.
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Specification