D3 Prep Water Meters PT2

New Meter Testing

Should be tested before installed, states allow a representative sample of new meters to be tested for accuracy, if the tested meters prove accurate, the rest of the lot is assumed to read accurately as well.

Testing Frequency

• Meters deteriorate/metering accuracy goes down.

• Older meters benefit the customers while water utility loses revenue.

• Meters should be tested & repaired or replaced as required.

• No national standard has been frequency

• Most states that have established frequencies require that larger meters are tested more frequently than smaller meter.

Testing Procedures

• Run several different flow rates over the meter’s operating range to determine meter efficiency

• A known volume of water is passed through the meter at different flow rate.

• Determining if the meter meets acceptable accuracy limits for use.

Testing processes

Three ranges of flow are typically tested

• Maximum

• Intermediate

• Minimum

• For larger current and compound meters, 4 or 5 flow rates are tested

• Large meters are typically tested in the field while small meters r removed and brought back to the meter shop for testing.

• Only the lower 5-10% of range is tested since this tends to be the range where accuracy falls off and the upper ranger requires large volumes of water which makes it difficult to perform.

Current Meters

Commonly called velocity meters, are usually installed on water lines that are 3in or more in diameter

• Turbine, MultiJet & Propeller

Turbine Meters

The flow of water causes a rotor to rotate within a measuring chamber that is recorded on the meter’s register.

• There is nearly a directly proportional relationship between the number of revolutions of the rotor and the volume of water that passed through the meter.

• The meter requires a minimum flow rate b4 the blades will begin to rotate which means this meter is best suited for high flow applications.

• Very low friction loss, unless sediment accumulates on the blades then meter would under register

MultiJet Meter

• Has a multiblade rotor that is mounted on a spindle within the cylindrical measuring chamber

• Water enters the measuring chamber through many orifices around the circumference

• clogged meter will over register while worn meter will under register

Propeller Meter

• Water causes a propeller to rotate and this movement is transmitted to register to record the flow.

• Propeller doesn’t take entire diameter of pipe, meter used when flow is fairly consistent and does not change abruptly.

Proportional Meter

• Has restriction in the pipe that requires a portion of the flow to go through a meter and be recorded

• Has Multiplication factor, meter reading must be multiplied to get actual flow through the system.

• Is accurate and have minimal friction loss

Venturi meters

• Pressure can be compared by mechanical or electronic instrumentation then converted to a flow rate and totalized flow

• Are accurate, Minimal fraction loss & require little maintenance.

• Has been used for many years to measure flow through large diameter pipelines

• The main inlet has the highest pressure and whilst in the throat area pressure is @ its lowest

Orifice Meters

• Has a thin plate that restricts flow through the system and creases a differential pressure on each side of the plate.

• The differential pressure is proportional to the flow rate

• Major disadvantage is the head loss it produces

Magnetic Meters

• A conductive material moving through a magnetic field will induce a voltage

• A magnetic field is established across the pipe by the magnetic (mag) meter while water acting as a conductor flows through the magnetic field which causes a voltage.

• Voltage produced is proportional to flow

• Meter is very accurate and well suited for dirty water/corrosive since they have no moving parts

• meter has very little headloss

Ultrasonic Meters

• Uses sound generating and sound receiving transducers to send and receive sound waves through a pipe with flowing water.

• The flowing water changes the frequency of the sound waves due to the Doppler effect.

• This frequency change is proportional to the flow rate.