Measuring and testing – Volume or rate of flow – By measuring thrust or drag forces
Reexamination Certificate
1998-07-16
2001-04-10
Patel, Harshad (Department: 2855)
Measuring and testing
Volume or rate of flow
By measuring thrust or drag forces
C073S861710
Reexamination Certificate
active
06212958
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a flow sensing assembly and method for detecting the flow of fluid through a flow passage and, more particularly, to a flow sensing assembly and method for detecting the presence of fluid flow in low flow applications.
This invention has particular (albeit not exclusive) application to the lubrication of bearings. There are a variety of systems on the market which are used for delivering lubricant to bearings. In many cases it is desirable to monitor whether lubrication is accomplished in a timely manner, especially with respect to critical bearings which might otherwise fail. Monitoring can be carried out by manual examination of the bearing or by a system which automatically detects flow of lubricant to the bearing. However, where the quantities of lubricant delivered to the bearing are small, reliable detection is difficult to achieve. This is due at least in part to the unavailability of an effective yet inexpensive sensor which is capable of detecting the flow of even small quantities of material through a flow line.
Reference may be made to U.S. Pat. Nos. 2,943,486 and 4,143,255 disclosing various devices in the field of this invention. U.S. Pat. No. 2,943,486 describes a flow sensor which is designed to extend into a flow passage and obstruct the path of fluid flow so that the flow rate of the fluid may be determined. While able to detect the presence of fluid flow under high flow conditions, such sensors typically do not extend across the entire flow passage and thus do not effectively detect the presence of fluid flow in low flow applications. Consequently, the use of these sensors in a lubrication line would likely result in excessive lubrication, increased expense and reduced performance.
U.S. Pat. No. 4,143,255 discloses a flow sensor having a spring-biased paddle which extends into and across the flow path during static or “no-flow” conditions. The flow of fluid causes the paddle to align itself parallel with the fluid flow during “flow” conditions, and an associated switch or magnet determines whether the paddle is in the “no-flow” or “flow” position. However, these sensors do not effectively detect the presence of fluid flow in low flow applications. As an example, low flow may fail to pivot the paddle into the “flow” position because of the force of the spring in addition to the static fluid pressure on the downstream side of the paddle. Moreover, once the paddle is in the “flow” position, the upstream static fluid pressure may prevent the paddle from returning to its “no-flow” position. This is especially true in applications involving highly viscous materials such as a lubricant. Sensors which use a magnet to signal movement between the no-flow and flow positions suffer from the further drawback that a nonmagnetic material must be used so that the sensor will not interfere with the magnetic field.
SUMMARY OF THE INVENTION
Among the several objects and features of the present invention may be noted the provision of a flow sensor assembly and method capable of detecting the presence of fluid flow under low flow conditions; to provide such an assembly and method capable of detecting the presence of fluid flow where there is a static head of fluid in the flow passage; to provide such an assembly and method capable of detecting the presence of flow in highly viscous fluids; to provide such an assembly which may be conveniently installed in a fluid flow line such as a lubrication line; to provide such an assembly and method capable of extending the life of a critical bearing by reliably detecting the flow of lubricant to the bearing; and to provide such an assembly and method which is simple in construction for economic manufacture.
Briefly, the flow sensing assembly of the present invention comprises a sensor body having a flow passage therethrough, and a resilient blade having an end which is fixed relative to the sensor body and an end which is freely movable. The blade extends as a cantilever from its fixed end to its free end into and across the flow passage generally broadside with respect to the direction of flow so that fluid flowing through the flow passage causes the free end of the blade to deflect in a downstream direction from a no-flow position to a flow position. The free end of the blade returns to its no-flow position upon stoppage of flow. The assembly also includes a detecting device for detecting deflection of the blade due to flow of fluid through the flow passage and for producing a signal indicating the occurrence of fluid flow.
This invention is also directed to a method of detecting the flow of fluid through a flow passage in a sensor body. The method comprises the step of mounting a blade so that it extends into and across the flow passage from an end of the blade which is fixed relative to the body to an end of the blade which is freely movable so that fluid flowing through the flow passage causes the free end of the blade to deflect in a downstream direction. The method also includes the steps of intermittently pumping fluid through the flow passage, detecting deflection of the blade due to flow of fluid through the flow passage, and generating a signal indicating the occurrence of fluid flow in response to deflection of the blade.
Other objects and features of the present invention will be in part apparent and in part pointed out hereinafter.
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Lincoln Industrial Corporation
Patel Harshad
Senniger Powers Leavitt & Roedel
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