Page 88 - Water Loss Control

70 Cha pte r S i x

FIGURE 6.5 Source meter replacement at raw water pumping station: New 48-in diameter
magnetic meter has been lowered into its chamber and work is underway to make connections
to the raw water transmission piping. (Source: Philadelphia Water Department.)

Traditional source meters are the full pipe bore type; or meter designs that con-
sumed the entire pipe diameter. Some of these meters, such as propeller meters, induce
a head loss through the pipe since part of the meter apparatus exists within the flow
stream of the pipe. Full bore meters, particularly in larger sizes are costly and require
considerable space. Water pipelines must be shutdown and dewatered to replace these
meters. Still, many full bore meter types and brands have proven histories of reliable,
accurate service for periods of many decades. In recent years, insertion-type metering
devices have witnessed considerable evolution. These meters offer advantages of lower
cost, less arduous space requirements and no need to shutdown/dewater the pipeline
to install the meter. Insertion meters can be installed in ferrules that can be tapped while
the water pipeline remains in service. The insertable electromagnetic averaging flow
meter is one type of reliable insertion meter available today.
Many reliable types and brands of flowmeters exist in the commercial marketplace.
Water utilities have many options at their disposal in selecting meters. The challenge
becomes making the best reasonable meter decision to match the desired application in
the field.

6.4 Source Meter Accuracy and Testing Program Steps
Treated drinking water is commonly measured by meters, but untreated source water
from lakes, reservoirs, streams may be measured by other devices, such as Parshall
flumes or weirs. Any unreasonable degree of error in a measuring device must be dis-
covered and corrected; incorrect supply data compromises the water audit since any
error in the source meters carries throughout the audit.