The development of a curb valve flow meter for gas theft detection

Abstract

As the supply of natural gas continues to dwindle, and government decontrol of pricing progresses, the rising cost of this essential natural resource will drive more individuals to consider various forms of pilferage as a way of reducing their financial burden. Today, according to numerous gas utilities, significant revenues are being lost via theft of service, losses which are ultimately passed on to the businesses' honest customers.

A method to detect such thievery developed at the Massachusetts Institute of Technology for Consolidated Edison of New York, was the design of a secondary flow metering device. Located outside a suspected concern, and placed within the small confines of a modified valve or pipe structure, its function is to act as a cross reference for the existing positive displacement meter. The concept chosen was the phenomena of vortex shedding, a fluid oscillatory instability which is used extensively as a measuruing technique in the process control industry. Feasibility studies were carried out using a flat, non-moving bluff shedding element and a piezo-electric bimorph ceramic cantilevered behind it. Both elements were situated within a curb valve based prototype design having a test section inner diameter of one inch. As predicted, experiments demonstrate a repeatable, linear relationship between frequency of oscillation and volume flow for flow rates between 200 and 1000 CFH. A requirement of less than one inch of water column pressure drop across the test section was also achieved. The output signal of the bimorph varied from millivolts to several volts throughout the same specified flow range. In addition, the oscillations may be simply counted to yield and integration of the total volume delivered.

The success of the concept suggests that a Phase II program, in which the laboratory design is incorporated into a device suitable for rigorous field tests by the utility, should be pursued.