An integrated Smart Water system is an effective platform for

uncovering costly flow meter errors by exposing mismatches

between, inter alia, measured flows, power usage and pump

system design. Over read meter flows undermine well production

plans, distort operational efficiencies, and bias regulatory reports

that could lead to unfavorable actions against future water

exploitation.

 

Flow meters are crucial for production planning, monitoring, maintenance and regulatory report accuracy, but even a well calibrated meter in excellent operating condition can render inaccurate readings. Flow disturbances are a common cause of errors.

 

McCrometer – a leading flow meter manufacturer - reports that flow disturbances can cause meters to under read or over read, depending on the disturbance, flow velocity and metering technology. The company states that the error can be great: “For example flow disturbance caused by a butterfly valve can result in erroneous readings of over 50 percent for certain meters.” (McCrometer technical article, Flow Conditioning).

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The design of the pipe system and placement of the flow meter are crucial to achieving accurate flow readings. Critically, a full discharge pipe without large air spaces is required for a flow meter to perform properly. A discharge pipe that is placed at a higher level than the water discharge point will allow spaces to form and lead to inaccurate readings.

 

If a pipe is not full, the flow meter will give inaccurate results because the meter measures the velocity of the liquid as it passes through a specific area. If the sensor is always completely submerged but the pipe is not full, the meter will still calculate flow based on the area of the full pipe, resulting in a flow reading that is too high.

 

The simplest fix can be to install the pipe on a vertical section. If the pipe downstream of the meter is horizontal or tilted so that the flow is going downhill, the pipe must be modified so that a rise of at least one pipe diameter is downstream of the meter, with a continuous acting air vent placed immediately upstream of the meter or at the highest point close to the meter, to prevent air pockets from building up in the vicinity of the meter.

 

Actual flow data on a water well in the Central Valley illustrates the potential magnitude of meter errors. Prior to realigning the height of the discharge pipe of the subject meter, the propeller meter read 1,450 gallons per minute. After realignment the flow meter read 1,250 gpm – still higher than the best operating point on the pump curve of 1,038 gpm. The installation of a new flow sensor and air vent adjustment brought the readings down to just below 1,000 gpm.

 

Further investigation of flow meter readings of other production wells revealed a similar over reading bias and necessitated corrective action and changes in well production and dispatch plans for the upcoming peak demand period.

 

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