World Toilet Day, observed Nov. 19, calls much needed attention to global...
Part 1: Water Meters
One-size-fits-all is not in the vocabulary of most water
utilities when it comes to water service entry lines. The water service entry
into a building can be simple or complex depending on the building and what it
contains. Even water services for residential homes can be points of
controversy under the right conditions. Sound confusing? It really should not
be if the local municipality/utility has a set of regulations in place that
clearly spells out how the water service is to be installed and what components
are placed in the water service line as well as by whom and at what cost.
There are three important components that must be considered
for a water service entry line--the water meter, a local/remote reading device
and a backflow prevention device. Usually, backflow preventers are considered
only for commercial/industrial applications, but they also should be placed on
residential service lines when the residence is used as a commercial
establishment (e.g., hair salon, dog grooming, photo processing, etc.). Under
the right conditions, these dwellings can be a source of contamination.
However, finding these home businesses might be difficult, as they often do not
hang a sign advertising their presence.
This series of articles will describe each of the separate
functions or components of the entry line as individual items and will detail
how each can be used or placed. Additional information within each article will
describe the operating characteristics of each device as well as some tips on
maintenance and service. The articles will not cover water shutoff valves or
Water meters are always the most interesting to discuss
because everyone knows their importance in generating revenue for the utility.
(At least the author hopes your meters are generating revenue.) However, water
meters also provide such important information as recording the flow, providing
production versus consumption usage, helping identify leaks at the property and
identifying illegal water usage. The latter occurs when the property owner uses
water from other than the potable water connection.
Water meters are manufactured by a number of different
companies and in a number of different styles. The one point to remember is
that most water meters are made in accordance with standards that were
developed within the industry. Meters manufactured for use in the United States
are made in accordance with American Water Works Association (AWWA) standards
(Table 1). This means that the physical construction has uniform dimensions and
that the internal parts of each type also have some similar characteristics
although they are neither alike nor interchangeable.
Meter selection always is based on the utility's preference
and experience. Most utilities use two or three different types from one or
more manufacturers. The type selected should be based on the maximum cold water
flow through the service line to the building. Residential meters usually are sized
for 3/4" (or slightly smaller) and are connected to a 1" service
line. The smaller size meter is acceptable because the residential water flow
seldom exceeds 25 gpm (the nominal flow for the meter). In cases where flow is
greater, a 1" meter can be installed, but this often reduces the meter's
ability to accurately record leaks or very small flows (1/8 gpm or less).
However, most 3/4" meters at 25 gpm can handle two water hoses and a
flushing toilet without any adverse effect on the water flow and pressure.
Multi-family, commercial and industrial water meters should
be sized for the maximum anticipated flow and not the size of the service line
entering the building. There are published tables that can assist the utility
in determining the proper size for different properties and applications based
on the number of fixtures and the approximate use.
Water services that require meters greater than 2" in
diameter need a compound meter. Compound meters are constructed with a small
meter (3/4" to 1") for low flows and a larger meter for the higher
flows. This arrangement permits the utility to capture all of the low flow
usage that occurs when a single faucet is turned on for brief periods of time.
Buildings that are constructed with fire sprinkling systems
also should be equipped with a water meter on the fire protection system. In
some cases, the fire line is separate from the potable water service
connection, while in others only one large service line is connected to the
building, providing both demands.
Buildings that have separate fire protection systems should
have a detector check meter that records the fire line flow. Additionally, the
meter should be constructed with a small meter to record any small flow that is
used. Another option is the use of a compound and fire flow meter combination.
Small Meter Construction
Water meters come in four basic types of construction:
positive displacement, multi-jet, single jet and turbine (Figure 1).
Additionally, there are some electronic meters, but their use is not as
widespread. The designations refer to the flow of the water through the meter
and the manner in which the flow is measured and recorded.
The meter case can be made of bronze, brass or plastic and
usually is available in the different materials from any given manufacturer.
The internal measuring chamber is made of a thermoplastic compound and is
replaceable as a unit. The register or recording component is mounted outside
of the case and often is magnetically driven. There still might be some very
old mechanical drive meters in use, but those are rare.
Operation of the meter-measuring chamber varies with the
different meter construction types. Positive displacement type meters generally
are constructed with a nutating disc or oscillating piston in the measuring
chamber. Water enters the chamber through a port in the side and flows across
and through the disc or piston, discharging through another side opening.
There is a different action that takes place within each
device that measures the water flow. Oscillating piston meters transfer their
motion to a spindle mounted in the top of the case that is fitted with a
magnet. Water flowing across the piston rotates the magnet that then drives the
Nutating disc measuring devices wobble within the chamber
and do not rotate. However, the wobble motion is restrained in a lower ball and
socket and only the small spindle on the top has a circular motion. This
circular motion is transmitted by a connecting link into rotary motion that
drives a spindle-mounted magnet outside of the chamber. This magnet actuates a
secondary device in the recording mechanism.
Multi-jet meters also are made with a removable
thermoplastic measuring chamber. However, in these meters water enters the
bottom of the chamber and flows upward past an impeller (or rotor) that looks
like a series of vanes extending from a hub that is mounted on support shafts.
Water flowing past the vanes causes them to rotate on their axes. The upper
shaft has a magnet located on its end and transfers the rotary motion of the
impeller to another device in the recording head.
Some new styles of the multi-jet meter are made with a
special exterior case placed at right angles to the threaded service line
connections. This setup permits water to enter on the side of the case and then
flow upward through the impeller. The advantage is that the meter service line
does not have to be horizontal while still metering the water flow as if it
were on a horizontal plane.
Single jet meters consist of a bronze, brass or alloy case
that houses a measuring impeller and a chamber placed slightly off-center from
the water flow connections. Water entering the case is directed through a
single orifice into the impeller chamber. Water flowing tangentially past the impeller
causes it to rotate on its supporting axis. This rotation drives the magnetic
coupling on the recording head.
Turbine meters usually are made of bronze or brass
materials, although some other alloys might be used. The measuring chamber is
made of a thermoplastic material and is removable from the main case. The
impeller (rotor) is mounted horizontally within the measuring chamber on a set
of support spindles/shafts. The measuring chamber often is fitted with a series
of straightening vanes that control the direction of the water that enters the
Water passing through the chamber causes the impeller to
rotate. Since this rotation is parallel to the water flow, a set of worm or
bevel gears is needed to change the motion direction so it is perpendicular to
the water flow. This change in direction allows a magnet located on the end of
the shaft to be magnetically coupled to the recording device on top of the
A variation of the turbine meter is the propeller meter.
This type of meter uses a tapered and curved impeller placed in an open pipe to
register the flow of water. These meters are used as production (wells and
plant discharge) or fire hydrant meters and not as consumption meters, because
of their inability to register low flows.
Large Meter Construction
There are several different styles of large meters used for
commercial, multi-family and industrial applications. However, these meters do
not have special or different methods of measuring the flow of water. Instead,
they use a combination of one or more of those types of meters (positive
displacement, turbine, etc.) previously discussed.
Some meters (11/2" and 2") used in four- to
six-unit multi-family buildings still may be a single unit meter much like
those previously described. The only difference is in their physical size, the
maximum flow capacity (120-170 gpm) and a loss of low flow accuracy. However,
if the building has other occupancy or has a higher flow, then generally a
compound meter is used.
The advantage of a compound meter over a single meter is in
its ability to capture low flows more accurately, while still accommodating the
same high flow and fitting into the same general space. For example, one
2" disc meter has a flow range from 11/2 gpm to 170 gpm, with a continuous
rating of 100 gpm. A 2" compound meter from the same manufacturer has a
flow range from 1/4 gpm to 170 gpm continuous flow. If this were a six-unit
apartment, about 15 to 20 percent of the water used would be less that 11/2
Compound meters usually are manufactured in sizes from
2" to 6" and have different flow ranges for each size. Generally, the
low flow measuring range is somewhere between 1/4 gpm and 1/2 gpm, with the
high flows extending to approximately 1,500 gpm. Some manufacturers also make
8" compound meters that range from 1 to 2,000 gpm.
Compound meters (Figure 2) generally consist of a small
meter that can measure up to 25 gpm and a turbine meter that handles the
remainder of the flow. Most manufacturers place them in a single cast bronze or
brass housing that is made with flanged connections. Since all are manufactured
in accordance with AWWA standards, the external dimensions usually are the
same, with some physical differences. Additionally, some manufacturers make
compound meters with other than a single body so they can accommodate their
individual meter styles.
Those meters that share a common body usually have some sort
of a diverting plate or valve device located within the main body of the meter.
The purpose of the diverting device is to direct the flow of water to the
proper section of the meter. Therefore, when the flow becomes greater than the
upper limit of the small meter, the gate opens and the water is directed to the
high flow turbine or recording device. In some instances, the compound meter
has individual recording heads for the separate measuring devices, while in
others a single recording device is supplied.
Fire line meters are another large style meter that usually
are found in industrial, commercial and multi-family (apartment or condo)
buildings that have fire suppression systems. However, these meters are made in
a variety of types (Figure 3). The one selected for any given application will
depend on the utility serving the property and the regulations that they
follow. Not all have the same requirements.
For example, some utilities are not concerned with how much
water is used within a building's sprinkling system. For these applications, a
simple detector check with a small bypass meter will only record the small
amount of water that is used for testing or flushing and almost no water if the
system is activated. Other utilities want an accurate record of all water used
and require fire line meters that are fitted with compound and main line meters.
These usually are 6" to 12" meters.
As a rule, the measuring chamber of the fire line meter is a
proportional type meter and is not made with an individual housing or chamber.
Instead, the measuring section is similar to a multi-jet chamber that is placed
in the top of the case. The placement of the measuring section permits a clear
path for the fire suppression system water to flow through the meter. It also
prevents damage to the measuring section in case a contractor left something
large in the pipe. However, many new installations require a strainer placed
ahead of the meter to prevent such damage from occurring. These strainers are
sized and manufactured so that there is no restriction to the water flow.
Meter Size and Selection
Selecting a water meter for a building usually is based on
previous experience or existing criteria. If there are no previous data
available, selection should be based on the demand or anticipated consumption
of the building using some existing device flow formulas. This meter should
never be based on the size of the water service line, unless the building has
Developing a water demand for an application is not
difficult, but it does require a set of building plans or an on-site
inspection. Since an on-site inspection can be done only with the building
nearly complete (a little late to be selecting a meter), the plans usually are
necessary. The best time for the plan review is during the permit application
and before any construction begins.
Most meter manufacturers, as well as the AWWA, have tables
giving the consumption rates of different building fixtures. Using these tables
and counting the number of fixtures will provide a maximum building demand.
This amount then can be modified to an actual demand by estimating the number
of fixtures that will be used at any given time.
For example, if the building was a four unit multi-family,
the water demand could be based on three of the four units using similar
fixtures at the same time--such as showers in the morning combined with a
couple of water closets (toilets) and lavatories (wash basins). This projected
maximum flow in gallons per minute then can be checked against the meter
manufacturers capacity for a given meter size. If the projected flow was 50
gpm, then a meter having a standard flow capacity above this would be required.
Most meters have an excess capacity over the normal
operating range. However, this excess should never be used as the basis for
meter selection. It only provides a cushion for peak flows that do not have a
long duration. Again, remember to ascertain the low flow rating on the meter.
Capturing the leakage flow that occurs in older buildings not only provides
revenue but also can assist the utility in alerting the building owner of a
problem and save water.
Full size meters can be used for industrial applications
that have large service lines. Even if a building does not currently have the
domestic demand for an 8" line, it is easier to install an 8" fire
line or compound meter than to try and calculate what the building consumption
will become in future years. When the service line (16" to 24") is
greater than a meter size, the service can be manifolded to accommodate two or
more small size meters that would provide an equal amount of flow as the
Buildings (warehouses or commercial) that have fire
protection systems, but only a small water demand require a different method of
selecting the water meter. For these applications the potable water for the
building often is tapped off of the main line and does not require a full-size
meter. To be most efficient, the fire protection system should be fitted with a
detector check meter (including a strainer) and the small line should have a
meter that meets the required demand of the fixtures.
All water meters should be installed in accordance with the
manufacturer's instructions. They should be located in an accessible location
that is protected and has ample room in which to work. If the meter is a
compound or larger type, then consideration must be given to the size or style
of test equipment that will be used. It must factor in the ability to discharge
test water safely without causing any water damage to the building.
Since many electricians ground the electrical system to the
water pipes, some consideration must be given to providing protection to the
meter and anyone working on the system from stray electrical currents. Usually,
this is accomplished by installing a jumper wire across the meter, as well as
grounding the electrical line to the incoming side of the service line. Much
new construction, because of changes in the electrical codes, requires a
separate grounding rod for the electrical service located outside of the
building. In some cases, this is required because the new plastic service lines
being installed do not provide a grounding capability.
Meter testing often is a controversial subject. For
starters, it requires money. It also is an inconvenience to the property owner,
as well as a disruption to normal daily routines. However, in almost all cases,
the cost of meter testing and replacement (if necessary) is more than offset by
an increase in revenue during the life of the meter. This is especially true
for areas that have average or higher water rates. A thorough and
well-thought-out plan is the best approach.
The frequency of meter testing depends on several factors:
meter size, quality of water, usage, service calls and application being the
most common. Manufacturers and other associations (AWWA) have recommended
standard times for meter test cycles that have proven satisfactory over the
years. Many utilities also have established programs that they gladly will
share with interested parties.
As a rule of thumb, most residential meters should be
checked at a 10- or 15-year interval. A test sample of a few meters within a
given area will help you determine the present meter accuracy. This can be
accomplished using a portable test meter any time there is a service call to
check a low registering meter or a complaint of a high water bill (presuming
there are no leaks).
If the meters are relatively accurate (95 percent) then a
total testing program can be delayed. Lower accuracies are a catalyst for a
total test program. If the utility experiences a lot of service calls for
stopped meters, then a testing program should be started. Further, if many of
the meters show large inaccuracies, then a changeout and repair program should
be initiated without going through a testing program.
Large meters should be tested more frequently, especially if
the building uses a great amount of water. The rationale is that the low flow
meter sizes often fall behind in their registration, causing the utility to
have an increased amount of unaccounted for water and resulting in a loss of
revenue. In some cases, the cost of testing and subsequent repairs may be more
than the gain from lost revenue, but the testing program frequency should not
Testing larger meters at two- to three-year intervals might
seem excessive to some, but it should be cost effective in most cases. This is
especially true for multi-family buildings (or apartments/condos) where there
is a lot of low flow usage (e.g., toilet flushing and wash basins/sinks). If
there is any concern about the cost benefit, a record of the test costs versus
revenue gain can be used as a basis for the testing program. The test time also
will provide the utility a chance to make a vital inspection of the meter to
check for tampering or other problems.
A water meter is tested in a variety of ways. For
residential meters, it is easier to do a change out and bench test the meter
than trying to test within the house. However, there are portable test meters
that can be used within the house that give accurate results. Larger meters
usually can be tested only in place, which means having to shut off the water
or provide some other means to supply water while the test is going on. Having
a locked bypass line around the meter will allow the building to have water
while the test is being done.
In other cases, the building might be served by two or more
lines (common in hospitals), thus permitting one to be shut down at a time. If
there is no other way of providing water while the meter is being tested, then
arrangements have to be made for the test to be done at other-than-normal
working hours. Usually this involves a lot of coordination and overtime pay.
Still, this testing must not be ignored or put off. After all, it is revenue
and unaccounted-for water that is at stake.
Photos courtesy of Hersey Meters, Cleveland, N.C.