While *most* flow meters will work well on water service, there are
meters specifically designed for water service, providing the best
combination of cost vs. performance. A typical cold water meter will
have a bronze or plastic body with plastic internals.
A few meter designs dominate the cold water meter market including
oscilating piston, nutating disc, and multi-jet. They all have their
particular
advantages, but all cold water meters must meet minimum specifications
set forth by the AWWA.
For hot water meters you are limited to multi-jet or other 'turbine-type'
meters. P.D. meters cannot be used for hot water service.
Water Meter Sizing
You call and say that you want a 3/4" meter for water service.
If the person you are talking to knows meters and wants to give you
the best possible selection, he will say "Do you want a 5/8 x
3/4 or a 3/4 x 3/4?" The normal reaction is "Why would I
want a meter with a 5/8" inlet and a 3/4" outlet?" Fortunately,
that is not what these fractions mean.
At one time, before design improvements which have come about in the early '90's,
we would tell people:
The first fraction is the chamber capacity:
5/8 meant a 25 GPM capacity with a 13 psig pressure drop
3/4 meant a 30 GPM capacity with a 13 psig pressure drop
1 meant a 50 GPM capacity with a 13 psig pressure drop (seldom used)
Note that the second fraction is not the meter end connection, but the line size
the meter will install into when the coupling connections are used. The cases
on meters which comply with AWWA C700 (American Water Works Assoc) have straight
threads, which are 1 line size over the size pipe. Here are the actual threads:
5/8 x 1/2 meter Actual end threads are 3/4 x 14 TPI, NPSM (male)
5/8 x 3/4 meter Actual end threads are 1" x 11 TPI, NPSM (male)
3/4 x 3/4 meter Actual end threads are 1" x 11 TPI, NPSM (male)
1" meter Actual end threads are 1.5 x 11.5 TPI NPSM (male)
Why this straight thread? The meter is designed to be periodically removed and
tested. If the meter ends had tapered threads, the connecting pipe coupling rides
over the meter thread (interference fit). In order to remove the meter, the connecting
pipe must be pushed backwards to disengage the NPT threads. But the pipe is buried
under tons of dirt and will not move. By using straight threads and couplings
which utilize a gasket to seal the line, one can loosen the coupling nut, spring
the line slightly and pull the meter out.
If you try to screw a tapered coupling (FIP, NPT) to the meter, it will leak.
Use the couplings offered with the meters.
For more information on water meters, click on a link below:
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