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196 Cha pte r T w e l v e

(c) Air may be trapped in the hoses connecting to the meter tester. Flush the hoses and
rerun the tests.
(d) One or both isolation valves may be leaking, causing inconsistent tests. Check by
looking at the tested meter’s register low flow indicator for movement over a 1- to
5-minute period.
(e) The strainer is clogged with debris, or partially blocked.
(f) The test meter may be clogged with rocks or debris, or may have been damaged
during flushing.
There are many other causes for inconsistency of test data. Inconsistency problems must
be resolved before continuing or the validity of the test results will be questionable.
10. Continue testing of additional targeted large meters by referring to AWWA M6 Manual for
test rates on specific meter types. Use the test flow rates from the meter manufacturer’s
literature if these are available. It is also recommended to perform one additional test
at the average customer flow usage rate. This will provide important information on how
efficiently the meter is operating in the primary revenue producing flow rates.
11. When testing compound meters review the consumption rate at the changeover point
with the accuracy of the meter at that flow rate. Determining the exact crossover rate
requires use of a pressure gage and rate-of-flow display. Slowly open the rate control
valve. When a rise in the pressure gage needle is noted, the flow rate indicated by the
register is the crossover rate. If crossover is not detected, close the rate valve until the
gage drops back again. Repeat opening and increasing the flow until the crossover rate
is identified. This process may take practice but is worth the effort.

Source: Expanded version of Section 14.3.4 Water Loss Control Manual 1st ed.

TABLE 12.9 Customer Meter Testing: Procedure and Safety Checklist (Continued)

Manufacturers of meter test equipment typically provide detailed procedures for
conducting accuracy tests. In general, the tester is connected and the line flushed. As a
preliminary step, a brief test should be conducted at a relatively high flow to determine
if there are any leaks or unknown taps in the pipeline. The flow rate should be set
approximately to 50% of the meter’s capacity and the test conducted for 10 sweeps of
the dial for adequate resolution. After determining the accuracy of the meter, the test
should be rerun for half the volume. The second accuracy test’s results should be within
1/2% of the first test. If not, a leak or other uncontrolled flow of water may be compro-
mising the test. If the meter in question has a flow indicator, it may indicate water
movement as a result of downstream isolation valve leakage.
When conducting tests, it is suggested that no test be less than 1 minute long and
that the meter’s sweep hand make at least one complete revolution. The residual pres-
sure on the tester should never be less than 20 psi when running a high-flow test. Also,
for safety, the tester should not be operated on lines with static pressure exceeding
80 psi unless provisions are made to secure the tester.
The formal testing sequence should then initiate, first in the low flow ranges and
progressing to higher flows. Experience has shown that, when most meters begin to
wear, accuracy is first impacted at the lower rather than the higher flows. If a meter is
performing accurately up through the lower 25% of its capacity, it will normally test
accurately through the rest of the range. This is especially true on very large meters.