In order to have valuable flow test data, readings need to be taken accurately
and all necessary data collected. Gauges are checked regularly and recalibrated
as necessary. Preprinted flow test forms are used which include places for the
following information:
- Location
- Date
- Time
- Hydrant inventory No.
- Hydrant Model
- Water main size
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- Static reading at hydrant
- Static reading on main
- Residual reading on hydrant
- Residual reading on main
- Pitot reading
- Name of tester(s)
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At the hydrant.
Static, residual and pitot readings are necessary in order to determine
the hydrant's total available fire flow beyond just what the one test outlet is flowing.
The Hazen-Williams formula allows us to calculate this information based on the readings
taken during our single outlet discharge. This formula allows us to accurately calculate what
an engine could pump from the hydrant from multiple outlets and/or the large diameter pumper outlet.
On the water main.
Secondary static and residual readings taken somewhere close by on the same water
main is important in order to take a look at how the main itself is performing
and to calculate the reserve capacity of the main. This separate look is important since flow
to the specific hydrant being tested may be limited by the capacity of the
lateral serving the hydrant and the efficiency of the hydrant's design.
Date and time are important since there may be temporary heavy usage of
the water system, reservoirs may be at unusual levels or pumping systems
may be in operation. By recording dates and times, it can be determined if
these or other factors caused unusual readings during the test.
WHY WE TAKE THE READINGS WE DO
Different reference sources offer different examples of recommended readings to be
taken when flow testing of hydrants. Our testing standards are based on the following
objectives:
- We need to have accurate data that tells us how much water is available from
each hydrant in order to employ appropriate fire suppression tactics. (We may need to utilize
all available water but not place more or larger fire streams than the hydrant can supply.)
- We need to have accurate data that tells us how much water is available from
the grid in the event of a major fire that would require use of multiple
hydrants. (Can the grid support multiple hydrants flowing or will opening a
second or third hydrant grossly impact the flow from the hydrant(s) already
flowing?)
- We need data that will allow us to determine if a weak hydrant is the result of an obsolete
or degraded hydrant installation or mechanical problem, or whether the water main
itself is performing poorly. (This data is also important in locating choked valves
or other correctable factors that may be causing poor flow from a specific hydrant on
a documented strong main.
- We need data that ISO will accept when evaluating our water supply system.
(Water supply comprises 40% of a community's overall fire protection score.)
- We need data that is useful to water agency engineers in planning water system
upgrade needs, capacity for expansion, identification of weak distribution areas,
etc.
By measuring static, residual and pitot at the hydrant being flowed we get the
most accurate look at that hydrant's individual characteristics and efficiency.
We can calculate pretty closely what that hydrant can provide when pumped down
by a fire engine.
By measuring static and residual from a nearby location, such as a fire hydrant
adjacent to the hydrant being tested, or from a nearby residential water service,
we can take an independent look at the water main itself and estimate its capacity
with reasonable accuracy. Since flow from the hydrant is affected by friction
loss in the lateral, street valve and the hydrant bury, we need to take additional
readings from a "quiet" location where we can look at what is happening in the water
main without such friction losses.
The adjacent hydrant used to take secondary readings should not itself be flowing, but
merely have a cap gauge attached so that readings can be taken.
If the secondary reading is taken from a domestic line as opposed to an adjacent
fire hydrant, the domestic user should not draw water during the few seconds that
the test takes place to eliminate any chance of friction loss in the domestic service
line skewing the readings taken there.
Regardless as to where secondary readings are measured, static readings should be
recorded prior to any water flowing and residual readings recorded with the test
hydrant valve fully opened and water main pressure stabilized.
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