Master Meter Testing at Water Plants and Pump Stations. Jeff Cruickshank, PE

Transcription

1 Master Meter Testing at Water Plants and Pump Stations Jeff Cruickshank, PE NC AWWA-WEA Spring Conference Asheville, NC April 11, 2015

2 Presentation Outline What types of meters are used at WTPs and pump stations? Why test master meters? How are master meters tested? Examples of master meter tests

3 Types of Large Flowmeters Turbine & Propeller Orifice Plate Venturi Annubar Variable Area Mag Meters Ultrasonic Vortex

4 Propeller Meters Rotational velocity directly proportional to flow velocity Straightening vanes upstream Accurate within 2% 10:1 range Linear output No external power required Requires calibration factor Moving parts - maintenance

5 Venturi Meters No moving parts Long life Accurate within 0.75% 10:1 range Large, heavy, expensive Non linear output square root Tubing can leak or plug Inaccurate at low flow

6 Mag Meters No moving or wetted parts Accurate within 0.5% 30:1 range Linear output Short run of straight pipe Require calibration Moderately expensive

7 Ultrasonic Meters No moving or wetted parts Accurate within 1% 20:1 range Linear output Accurate to 0.1 fps Sensitive to air and noise Measure mean velocity, not weighted by area

8 All Types of Master Meters Need Symmetric Velocity Profiles Pumps, bends, and fittings distort velocity profiles Skewed asymmetric profiles produce inaccurate metering Swirl, crossflow and flow separation cause errors Straight pipe upstream and downstream is critical

9 Typical Velocity Profiles in Water Mains Theoretical velocity factor 0.5 for laminar flow Profile shape for turbulent flow depends on pipe size, roughness, and velocity Velocity factor, ratio of average to center velocity, quantifies profile shape

10 Velocity Factors for Turbulent Flow VF= *sqrt(f) Equation from hydraulics text VF= *V^-0.075*D^-0.085*C^ Equation solved for more familiar terms D= 30 V= 2.0 C VF Large variation with roughness V= 2.0 C = 140 D VF Higher in big pipes (flatter profile) D= 12 C = 140 V VF % % % Increases with velocity but within 2% of 2 fps

11 Why Calibrate Large Flowmeters? In-place conditions different than laboratory Distorted profiles and cavitation create errors Mechanical meters wear and calibration changes DP meters inaccurate if leaking or at low flows Mag & ultrasonic meters need periodic calibration Pump Station Meter

12 Need Meter Tests For Water Audits

13 Testing Meters at Booster Stations and PRVs Allows Audits within Each Pressure Zone Corrected meter registration gives total flow into each zone Billing and GIS provide water sold in each zone Calculate non-revenue water by pressure zone Track flow into each zone at night to detect leakage

14 Meter Testing not the Same as Calibration Calibration usually checks electronic or secondary meter components Apply reference signal Check indicated flow Does not check primary element signal producer Testing checks both primary and secondary meter elements

15 How to Test Master Meters Clearwell drawdown test Second meter in series Clamp-on meters Portable probes Mag meter probes Pitot tubes

16 Pitot Tube for Testing Meters Invented in 1730 No moving parts Directly measures velocity head as differential pressure between upstream & downstream tips Accuracy 1-2% for stable profiles at velocities > 0.5 fps Reversible for foolproof check

17 Pitot Tubes Require Taps for Insertion 1-inch minimum tap size 2-inch maximum tap size Air valve tap works if not offset diameters straight pipe upstream and 5 downstream Vertical clearance depends on pipe size Pipe at pitot tap must carry same flow as meter

18 Pitot Tube Measures Point Velocity v = c 2gd / 12 c is coefficient (0.9) v is velocity in fps g is feet/sec^2 d is differential in inches Differential recorded as a 4-20 ma signal 12 ma is zero dp Zero dp Check

19 Pitot Tube Positioned at Centers of 10 Rings of Equal Area to Determine Average Velocity

20 Flow Calculated from Continuity Equation Q = V * A V is average velocity determined from profile A is area of pipe calculated from inside diameter Inside diameter measured with pipe caliper

21 Meter Test Compares Pitot Tube Measurement With Registration on Meter Totalizer 30 Best Fit Average Maximum Minimum 25 Pipe Location - inches Velocity - fps Q = V * A Q = V / T

22 Procedure for Testing Master Meters 1. Measure inside diameter 2. Plot velocity profile 3. Read meter to start test 4. Record velocity 5. Read meter at end of test Pipe Location - inches Best Fit Average Maximum Minimum Velocity - fps City Greensboro, NC Type of Test Meter Tap Location Stoney Creek PS Tap Number Velocity F Nominal Size 16 inches Table E Co Caliper Size inches Area Corre PCR Range Zero Head 12: ma Forward: 10: ma inches Reverse: 10: ma 1.62 inches Test Head 11: ma DP Calibration 1.75 inches vs 1.88 Actual Test Date/Time 5/2/ :15 to 10:45 Rod being reversed from 10:29 to 10:30 TEST RESULTS inches fps Time ma inches fps Remarks :15: OK 2 10:16: OK 3 10:18: OK 4 10:19: OK 5 10:21: OK 6 10:22: OK 7 10:24: OK 8 10:25: OK 9 10:27: OK 10 10:28: OK 11 10:29:00 RevRod 12 10:30: OK 13 10:31: OK 14 10:33: OK 15 10:34: OK 16 10:36: OK 17 10:37: OK 18 10:39: OK 19 10:40: OK 20 10:42: OK 21 10:43: OK 22 10:45: Average OK

23 Example Showing Typical Test Results Velocity Factor = Best Fit Average Maximum Minimum 25 Pipe Location - inches Velocity - fps Test Date May 20-May Totalizer Registration - kgal Elapsed Time - minutes Pitometer Flow - mgd Totalizer Flow - mgd Totalizer Error -2.8% -2.2%

24 Example Showing Consistent Under-Registration Over Wide Flow Range

25 Example Showing Close Instantaneous Rate But 28% Over-Registration for Totalizer Test Data Test Date Apr WTP Totalizer Totalizer Registration - kgal 724 Elapsed Time - minutes Pitometer Flow - mgd Totalizer Flow - mgd Instantaneous Meter Rate - mgd Totalizer Error 28.2% Instantaneous Meter Rate Error 3.2%

26 Example Showing Consistent Meter Registration Regardless of Pump in Operation Velocity Factor = Pipe Location - inches Best Fit Average Maximum Minimum Velocity - fps Test Date May 2-May 2-May Pump 1 Pump 2 Pump 3 Totalizer Registration - kgal Elapsed Time - minutes Pitometer Flow - mgd Totalizer Flow - mgd Totalizer Error -2.4% -2.3% -2.5%

27 Example Showing Venturi Meters Accurate Except at Low Flow Rates

28 Questions