On the way to Steamboat Springs, Colo., the Town of Walden rests on a high glacial plain, just 20 miles from the Wyoming border in Jackson County. Situated in the center of a large open valley called North Park, the 608 residents (based on the 2010 census) of the town and the surrounding area refer to themselves as “North Parkers”.
The Problem
As is the case in many municipalities, the Town of Walden’s water treatment plant needed to change over time. The town found it had a requirement to measure finished water. Its original pump station design did not include a flowmeter. The town also had two common problems faced by municipalities when specifying and installing a retrofit flowmeter for a finished water application: limited real estate and space requirements, and a need for high-accuracy flow measurement. Added to that was another common challenge for local governments: the need to minimize both installation costs and ongoing maintenance costs for any new technology solution.
Typically, traditional liquid flowmeters require a minimum upstream and downstream straight pipe run in order to operate effectively and accurately. Most traditional flowmeter installations require from 10 to more than 40 straight pipe diameters upstream from the meter and five or more straight pipe diameters downstream. These straight pipe runs are needed to eliminate the effects of swirl and other pipeline disturbances caused by pumps, elbows, valves and other devices that negatively affect liquid flow measurement accuracy.
Often, as in the case of the Town of Walden, the required plant real estate for a standard liquid flow measurement solution was simply not available in this system retrofit situation. The town’s existing piping configuration had no space to allow for installation of a traditional liquid flowmeter, given the lay length requirements and the typical upstream and downstream piping space needed to achieve the accuracy of most flow measurement devices.
The town’s engineers consulted with Canyon Systems Inc.—McCrometer’s municipal representative, located in nearby Lakewood, Colo.—about a solution that would provide the best overall flow measurement. Accuracy was another important requirement in this finished water application. The engineers stressed the need for a flowmeter solution that would also minimize installation costs, given their installation space constraints.
The Solution
Working together, the town’s engineers and Canyon Systems evaluated multiple flow measurement options suited for municipal water system applications. The McCrometer VM V-Cone System municipal flowmeter was high on the list of considered instrument options because of its high accuracy, flexible installation requirements and versatile capabilities. It is a differential pressure (DP)-type flowmeter with a design that includes a self-conditioning cone within the meter.
This DP-type flowmeter is especially useful when irregular or crowded piping and equipment are in place because its self-conditioning cone design greatly reduces the straight pipe run required for accurate measurement. Other flow technologies—such as orifice plate, turbine or Venturi tube meters—often require complex or expensive construction in the area where the flowmeter will be installed, in order to install the upstream and downstream straight piping required to achieve the desired measurement accuracy.
This meter’s cone design actually conditions fluid flow to provide a stable flow profile that increases accuracy. It features a centrally located cone inside a tube. The cone interacts with the fluid flow and reshapes the velocity profile to create a lower-pressure region immediately downstream. The cone’s central position in the line optimizes the velocity of the liquid flow at the point of measurement. The result is a highly stable flow profile for measurement accuracy.
Prepackaged and ready to install, this self-conditioning DP meter features a built-in three-way valve that isolates the transmitter from the process fluid flow for easy maintenance without shutting down the pipeline. It arrives from the factory wet-flow calibrated, eliminating many of the common headaches that arise when adding a flowmeter to any existing installations.
The self-conditioning DP flowmeter selected by the Town of Walden reduces flowmeter straight pipe run requirements by up to 70% or more and needs only 0 to 3 straight pipe diameters upstream and 0 to 1 downstream to operate effectively. This flowmeter can be installed in close proximity to pumps in crowded plant retrofit projects by reducing the number of straight-pipe runs required by other meters. This installation flexibility results in real estate, pipe and labor cost savings that can actually exceed the cost of the instrument.
This flowmeter also met the town’s accuracy needs. This flowmeter operates over a wide flow range of 10:1 with low head loss and supports line sizes from 4 to 18 in. The accuracy provided by this flowmeter is dependent on the line size of each application. The range of accuracy is ±0.5% over the 10:1 turndown for between a 40- to 7,500-gpm liquid flow rate. In addition to the installation flexibility, the town’s engineers were interested in the flowmeter due to its consistent performance and low cost of ownership. The engineers liked the fact that the flowmeter requires virtually no recalibration or maintenance over an exceptionally long life. This low maintenance requirement allows the town to keep its operational costs down.
The town’s city engineers installed an 8-in. self-conditioning DP flowmeter. To ease installation, the 8-in. flowmeter was equipped with a flange connection on the inlet and a plain end connection on the outlet. These connections made it easier to mate the existing flange by Dresser sleeve piping connections.
Due to space limitations, the lay length of the flowmeter was shortened by 13 in. from the standard lay length of 34 in. to 21 in. The last consideration was to install the flowmeter downstream of a “Y” fitting with no straight run of pipe and upstream of an ell and a valve with no straight run of pipe.
Conclusion
This self-conditioning DP flowmeter was ideal for the town’s water plant retrofit and finished water application. The flowmeter selected and installed by the town is specifically designed to enable municipal water engineers to rely on it for consistent performance. It was just as easy to locate and install as the town anticipated that it would be.
A key benefit to the town’s engineers in selecting this flowmeter for their water plant application included the ability to measure finished water effluent with a high degree of accuracy. Additionally, the meter’s transmitter produces a 4-20mA signal for easy integration with the plant’s SCADA system.
The completed retrofit project provides the town with better water plant process control and accounting of water usage.
