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Isco Hot Tap Insertion ADFM Used for Pump Capacity Verification With 0.5 Pipe Diameters Downstream Straight Run

Pump performance curves or characteristic curves provided by pump manufacturers characterize the performance of the pump under ideal or “laboratory” conditions. Once installed in the field there are a number of conditions that could potentially impact the performance of the pump such as entrained air, impeller wear, improper operation, etc. Therefore end users may require field verification of a pump’s flow rate under field conditions either upon installation or years later to gauge the pump’s performance at the actual installation site.

Recently, Smith Pump Company, Inc. supervised the installation and startup of four vertical solids handling centrifugal pumps at a large municipal WWTP’s influent lift station located in Southeast Texas. As part of the installation supervision and startup, Smith Pump Company, Inc. performed field verification tests on the pumps. Two attempts were made to measure flow rates on the 42” vertical pipes at locations downstream of the four pumps using clamp-on flow meters. The clamp-on flow meters were unable to measure flow on three of the four pumps due to low signal strength and/or turbulence. On the fourth pump, located furthest away from the wet well’s influent pipe, the clamp-on flow meters were able to measure flow; however, the flow measurements were unstable and their average flow rates underreport flow by 2.32% and 8.79% when compared to the manufacturer’s pump performance curve. Due to the instability in the reported flow rates the clamp-on flow meter data needed to be confirmed by another technology.

In September 2012 C.C. Lynch & Associates, Inc. provided a Teledyne Isco Hot Tap Insertion ADFM flow meter and two In-Situ, Inc. LevelTROLL 500 logging pressure transducers to make another attempt at verifying pump performance. Due to the difficulty getting a boom lift into and maneuvering around the lower level of the lift station and the turbulence in the flow stream at a location closer to the pump, the decision was made to install the Hot Tap ADFM approximately 2’ upstream of a 90 degree elbow. There remained an obvious concern over turbulence with an installation this close to an elbow. However, the Hot Tap ADFM’s unique measuring principle combined with the high velocity within the pipe made this installation a success. LEM Construction provided and installed a tapping saddle with two threaded ports for the installation of the Hot Tap Insertion ADFM and an analog pressure gauge.

                                   

                                   Hot Tap ADFM Location                      Adjusting Insertion Depth of Hot Tap ADFM

 

The Hot Tap Insertion ADFM uses pulse Doppler velocity profiling technology to measure the velocity distribution within the flow stream via four independent directional acoustic signals. Each directional signal is segmented so that velocities are measured across the flow stream as opposed to one single point at the face of the sensor. As a result, the velocity measurement is 3 dimensional allowing for the installation in applications with limited straight runs and or other poor hydraulic conditions. In this application, velocity measurements were collected and averaged over a 1 minute period. Every 1 minute a total of 80 individual velocity measurements were made from each of the four velocity beams. Each of the four velocity beams was segmented into 23 velocity bins. Therefore, each reported measurement is actually an average of 7,360 velocity measurements that occurred within the cross section of the pipe in a 1 minute period.

The following video helps visualize the concept of the individual velocity bins measured from four independent sensors.

For the field verification test the pump was run at 511 RPMs for two hours while the flow meter and pressure transducers logged data. Raw data generated by the Hot Tap Insertion ADFM allowed C.C. Lynch personnel to evaluate the quality of the velocity data being measured rather than just assuming the flow rate generated by the meter was valid. Upon initial pump startup, the raw data indicated excessive aeration within the pipe which slightly skewed the flow rate low though stable. As the aeration decreased the flow rate slightly increased and averaged 43,125 GPM for the next two hours. Even with the close proximity to the downstream pipe elbow the raw data indicated that the Hot Tap Insertion ADFM was providing high quality data. The Hot Tap Insertion ADFM reported stable flow rates throughout the remainder of the test with a gradual increase in flow rates as the water level in the wet well rose.

The original factory pump performance test rated the pump at 40,200 GPM @ 43 ft of discharge head.  The LevelTROLL 500 pressure transducers were used to measure the suction and discharge pressures during the test which were later used to calculate the discharge head.  At an average of 36.4 feet of head, the average flow rate measured by the Hot Tap Insertion ADFM was 43,125 GPM, which is within 0.5% of the pump manufacturer’s factory test curve validating the performance of the pump to the manufacturer’s specification.

 

Flow Meter

Installation

Location

Head (ft)

Factory Test
Flow Rate

Flow (gpm)

% Error

Hot Tap ADFM

2’ upstream of elbow

36.4

43,341

43,125

0.50%

Clamp-On (lower level)

Lift Station Lower Level

39.5

39,998

39,069

2.32%

Clamp-On

2’ upstream of elbow

37.1

43,621

39,787

8.79%

 

For more information on the Teledyne Isco Hot Tap Insertion ADFM flow meter or to find out if this flow meter is suited for your application feel free to contact us.

 

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