Intelligence Report
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RepWars
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DOS Technical Services
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No strainer should be
used in a fire line without the approval of the Owner’s Insurance Underwriters
and/or the Authority Having Jurisdiction.
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BACKFLOW PREVENTION ASSEMBLY
INSTALLATIONS
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This
information reflects accepted design considerations based on experience in
implementing cross connection control programs and policies set forth by
the American Water Works Association, Environmental Protection Agency, USC
Foundation for Cross Connection Control and Hydraulic Research and various
state and local health departments. These recommendations outline what an
acceptable design and installation constitutes and are to be reasonably
interpreted.
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General Installation And Clearances
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All double check valve (DCV) and reduced pressure zone (RPZ)
backflow prevention assemblies are designed for in-line service and must be
installed to prevent freezing, flooding and mechanical damage with adequate
space to facilitate maintenance and testing. Ideally, the installation
should not require platforms, ladders or lifts for access. Adequate
clearances from floors, ceilings and walls must be provided to access the
test cocks and to allow the repair and/or removal of the relief valve and
check valves; as follows:
o
All assemblies should be installed with a centerline height from 30
inches to 60 inches above the floor or adjacent grade. Any installation at
a greater height should be provided with a fixed platform, a portable
scaffold or a lift meeting OSHA standards.
o
A minimum of 12 inches of clear space should be maintained above the
assembly to allow for servicing check valves and for operation of shut-off
valves.
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A minimum of 30 inches of clear space should be maintained between
the front side of the device and the nearest wall or obstruction.
o
At least 8 inches clearance should be maintained from the back side
of the device to the nearest wall or obstruction. This clearance may need
to be increased for models that have side mounted test cocks or relief
valves that would be facing the back wall.
o
All RPZ devices must have an 18 inch minimum clearance between the
bottom of the relief valve and the floor to prevent submersion and to
provide access for servicing and relief valve operation.
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Miscellaneous Considerations
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1.
All assemblies should be adequately supported and/or restrained to
prevent lateral movement. Pipe hangers, braces, saddles, stanchions, piers,
etc., should be used to support the device and should be placed in a manner
that will not obstruct the function of or access to the relief valve.
2.
Strainers are recommended prior to each backflow prevention assembly
on non-fire fighting water lines. No strainer is to be used in a fire line
without the approval of the Owner’s Insurance Underwriters and/or the
Authority Having Jurisdiction.
3.
The assembly should be sized hydraulically, taking into account both
the volume requirements of the service and the head loss of the assembly.
The head loss of the assembly is not necessarily directed proportional to
flow. (Refer to the manufacturers head loss curves).
4.
Before selection and installation, refer to manufacturers literature
for temperature ranges. All assemblies must be protected from freezing
temperatures and if installed where temperatures will reach 100 degrees F or
above, a hot water type assembly must be used. Consult manufacturers
specifications for recommendations.
5.
Thermal water expansion and/or water hammer downstream of the
assembly can cause excessive pressure. To avoid possible damage to the
system and assembly, use water hammer arresters, surge protectors or
expansion tanks as appropriate.
6.
All assemblies should be specified and installed with the
manufacturer supplied resilient seated shut-off valves integral to the
assembly.
7.
Water lines should be thoroughly flushed before installing the
assembly. Most test failures on new installations are the result of debris
fouling one of the check valves or the relief valve.
8.
All assemblies must be installed horizontally unless they are specifically
approved for vertical installation.
9.
Parallel installations should be considered where water service
cannot be interrupted and on water lines larger than 4 inches.
10.
Assemblies should not be installed in areas containing corrosive,
toxic or poisonous fumes or gases which could render the assembly
inoperable or pose a safety hazard to personnel.
11.
Because of the inherent design of a reduced pressure backflow
assembly, fluctuating supply pressure on an extremely low flow or static
flow condition may cause nuisance dripping and potential fouling of the
assembly. While not effective in all cases, the installation of a soft
seated check valve immediately ahead of the RPZ will often hold the
pressure constant to the assembly in times of fluctuating supply pressure.
12.
Where the distance between the water meter and the device is greater
than 10 feet, all exposed piping should be stenciled "Feed Line to
Backflow Preventer – DO NOT TAP" at 5 foot intervals.
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Most test failures on
new installations are the result of debris fouling one of the check
valves or the relief valve.
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Drainage Provisions
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Drainage
for backflow prevention assemblies should be provided for all installations
of DCV or RPZ to accommodate discharge during testing or draining of the
unit and for RPZ relief valve discharges, as follows:
1.
For RPZ devices, drainage capacity should be sized to accommodate
both intermittent discharges and a catastrophic failure of the relief
valve. Refer to manufacturers flow curves to determine maximum discharge rate
based on supply pressure or on-site pressure; whichever is greater.
2.
Discharge from relief valves must be readily detectable to
maintenance personnel either visually or by means of water level alarms,
flow indicator lights, etc.
3.
All drainage from RPZ’s must be by gravity drains. Sump pumps should
not be relied upon unless they are sized to accommodate the maximum
discharge rate and connected to emergency power supplies.
4.
An air gap must be maintained between the RPZ relief valve opening
and any discharge piping. The air gap must be at least twice the dimension
of the effective opening of the relief valve; but in no case less than 1
inch.
5.
Manufacturer’s air gap fittings may be utilized provided that they
maintain a proper air gap and do not enclose or cover the relief valve.
These fittings are only sized to handle intermittent and low flow
discharges. Additional drainage capacity may be required to accommodate a
catastrophic relief valve failure.
6.
Discharge piping from relief valves should be terminated a minimum
of one inch above any floor drain or other receiving receptacle.
7.
Interior storm sewer drains receiving discharge should be equipped
with backwater check valve.
8.
Sanitary sewer drains receiving discharge should be trapped and
vented.
9.
Exterior discharge piping must be terminated above grade in an area
not subject to flooding (generally one foot above the 100 year flood
elevation). The terminal end of the discharge piping must have a rodent
screen and securely supported.
10.
All exterior discharge terminals should be screened and kept free of
debris, ice, snow or any other obstructions that could inhibit discharge
flow.
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Pit Installations
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Primarily
due to considerations for access, safety and gravity drainage, it is preferred
that backflow prevention devices not be installed in pits. Where pit
installations are proposed, however, they should be designed:
o
To be watertight with gasketed manholes or access doors extending a
minimum of 6 inches above grade and located to allow natural light into the
pit during testing/maintenance.
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With stairways, ladders or step irons.
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For crane access for installing and removing large assemblies.
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With adequate horizontal and vertical clearances to allow access to
the device.
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With a full flow screened gravity drain terminating above grade for
all RPZ installations.
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With sump pumps or gravity daylight drains for all DCV
installations.
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With floors pitched to drain.
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With adequate ground cover to prevent freezing.
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With surface grading to divert runoff away from the entrance way.
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Semi-buried pits for berm installations may be necessary to satisfy
gravity drainage requirements.
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Exterior Above Grade Installations
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An
above grade installation is generally necessary to provide gravity drainage
from RPZ devices. The additional benefits of improved access and enhanced
safety are also realized with an above grade installation. Two companies,
"Hot Box" and "Hydrocowl", have designed prefabricated
insulated enclosures that provide heat, gravity drainage and removable
access panels for servicing and testing. As an alternate, wood frame,
fiberglass, steel, masonry or precast concrete structures may be utilized.
All enclosures should be designed:
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With a floor elevation that is at least 6 inches above finished
grade.
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To provide adequate clearances around the device to access the test
cocks, shutoff valves, check valves and relief valve.
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With electric heaters or heat trace wire for any water service used
year round.
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With provisions for natural or artificial light.
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With full flow gravity drains according to the drainage
requirements.
o
With security measures such as locking doors and panels, flow alarms
or flow indictor lights, power indicator lights, etc.
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All assemblies must be
protected from freezing temperatures and if installed where temperatures
will reach 100 degrees F or above, a hot water type assembly must be used.
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Installation Within A Building
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Where
containment at the property line cannot be achieved or is waived based on
extenuating circumstances, installation within a building is often desirable
as the unit can be installed in a mechanical room or other area that has
heat and light. Access and drainage considerations must also be satisfied
and the devices should be located to avoid physical damage, electrical
panels, areas of excessive heat, etc.
Interior
installations above grade level should be provided with adequate
clearances. Discharge can be directed to adequately sized floor drains or
through an exterior wall above grade and screened.
Interior
below grade or basement installations are acceptable for DCV’s. RPZ’s are
only allowed below grade where one or more of the following conditions can
be met:
o
Where an adequate gravity drainage system is provided to accommodate
a relief valve failure.
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Where water level alarms are installed to detect flow from the
device and alert maintenance or security personnel.
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Where sump pumps are sized to accommodate a relief valve failure and
are connected to emergency power.
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Where the floor area and volume below the device could accommodate discharge
from a relief valve failure. For 2 inch and smaller units, 2,000 cubic feet
is generally acceptable. For larger units, the time to submerge the device
based on the maximum discharge rate and floor area/volume should be no less
than 8 hours.
In
any of the above cases, the Facility Owner must be made aware of the
potential for water damage in the event of a discharge.
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Drawings
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Plans
and specifications for the installation of backflow prevention assemblies
should include the following:
1.
A site plan (to scale or with dimensions) of the facility containing
a general location map, name and address of facility, property lines,
buildings, the size and location of public water main(s) and all fire and
domestic water services, meter pits, yard piping and hydrants, pumper
connection(s), interconnections, and the location of the proposed backflow
preventer(s).
2.
A plumbing floor plan (plan view) or partial floor plan indicating
water services, proposed backflow preventer(s), booster pump system, floor
drain(s) and all nearby objects (examples: electrical panels, boilers,
chillers, storage tanks, fire pumps, fire sprinkler risers, etc.). The plan
must be drawn to scale or with dimensions indicated distance from walls and
all nearby objects.
3.
A vertical cross section(s) of the proposed installation with
elevations from floor, ceiling, outside grade and all nearby objects.
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Design Information
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The
Plumbing Engineer should provide the following design information to the
Facility Owner for operations and maintenance of the water systems:
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General use of water within the facility.
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The degree of hazard for each BFP device.
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Detailed explanation of BFP drainage provisions.
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Size and description of all fire and domestic water services.
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Actual or estimated maximum flow demand.
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Pressures – upstream and downstream of the backflow preventer during
peak design flow.
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Description of the fire fighting system.
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Description of the installation of the backflow preventer – indicate
the location of backflow preventer, drainage, lighting, heating, access to
unit.
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The elevation and location of the 100 year flood plain in relation
to the BFP. A reduced pressure zone backflow preventer must generally be
installed 1 foot above the 100 year flood plain elevation.
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Description of the booster pump system, answering the following
questions:
1.
After the installation of the proposed backflow preventer(s), will
the Net Positive Suction Head (NPSH) required for the proper operation of
the booster pump system be adequate?
2.
After the
installation of the backflow preventer(s) in the suction line to the
booster pump system, will the booster pump system operate properly at peak
demand to deliver adequate pressure to the highest elevation and/or most
remote fixture unit or any other operation requiring a certain pressure?
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RepWars
Copyright
© 1997 - 2006
DOS
Technical Services
All Rights
Reserved
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Certification and Testing
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After
an approval of plans has been issued and the assembly has been installed,
it must be tested by a certified tester. The Plumbing Engineer is then responsible
to certify that the installation complies with the approved plans and
specifications.
Assemblies
must be tested at least annually by a certified tester with the results
recorded.
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