What
is back-siphonage?
Back-siphonage is the reversal of normal flow in a system caused by
a negative pressure (vacuum or partial vacuum) in the supply piping. |
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What
factors cause back-siphonage?
Back-siphonage can be created when there is interruption of the
water supply due to nearby fire-fighting, repairs or breaks in water
supply mains, etc. |
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What
is backpressure-backflow?
Backpressure -backflow is the reversal of normal flow in a system
due to an increase in the downstream pressure above that of the
supply pressure. |
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What
factors can cause a backpressure-backflow condition?
Back pressure-backflow is caused whenever the downstream pressure
exceeds the supply pressure which is possible in installations such
as heating systems, elevated tanks, and pressure producing systems.
An example would be a hot water boiler operating under pressure
coinciding with a reduction or loss of water pressure below the
operation boiler pressure. The backflow condition would cause the
contaminated boiler water to flow into the potable water supply. |
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What
is a cross connection?
A cross connection is a piping arrangement which allows the potable
water supply to be connected to a contaminant source. The most
common example is a garden hose attached to a sill cock with the end
of the hose connected to a pesticide sprayer. A drop in water
pressure can cause these chemicals to be pulled back into the water
supply (backflow), contaminating a building or even a neighbourhood.
The contaminant then poses a risk for anyone using the water for
drinking, cooking, bathing, or other purposes. |
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What
is potentially dangerous about an unprotected sill cock?
The purpose of a sill cock is to permit easy attachment of a hose
for outside watering purposes. However, a garden hose can be
extremely hazardous because they are left submerged in swimming
pools, laying in elevated locations watering shrubs, attached to
chemical sprayers, etc. |
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What
protection is required for sill cocks?
A hose bibb vacuum breaker should be installed on every sill cock to
isolate garden hose applications thus protecting the potable water
supply from contamination. |
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What
is a cross connection control program?
A Cross Connection Control Program is a cooperative effort between
plumbing and health officials, water purveyors, property owners and
certified testers to establish and administer guidelines for
controlling cross connections and implementing means to ensure their
enforcement so that the public potable water supply will be
protected. The elements of a program define the type of protection
required, the responsibility for the administration and enforcement,
and a public education and communications plan. |
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What
is the difference between pollution and contamination?
Pollution of the water supply does not constitute an actual health
hazard, although the quality of the water is impaired with respect
to taste, odor or utility. Contamination of the water supply,
however, does constitute an actual health hazard: the consumer being
subjected to potentially lethal water borne disease or illness. |
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What
is meant by "Degree of Hazard"?
The degree of hazard is a commonly used phrase utilized in cross
connection programs and is simply a determination on whether the
substance in the non-potable system is toxic (health hazard) or
non-toxic (non-health hazard). There are three degrees of hazard;
severe, moderate and minor. For more information on hazard
classification refer to the cross connection manual. |
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What
is the difference between a toxic and a non-toxic substance?
Toxic substance is any liquid, solid or gas, which when introduced
into the water supply creates, or may create a danger to health and
well-being of the consumer. A non-toxic substance is any substance
that may create a non-health hazard, is a nuisance or is
aesthetically objectionable. Backflow prevention devices must be
selected in accordance with the type of connection and degree of
hazard. |
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Should
we be concerned?
Yes, to cause a situation that has the potential to harm the health
and well being of your family, co-workers, or neighbours, should be
a concern to us all. A cross connection in a home, place of business
is a danger to those in the surrounding community. You have a legal
and moral responsibility to ensure that our drinking water supply is
safe. If you need to know more about Cross Connection control
contact a Committee Member near you. |
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Have
there been any recent cases of backflow incidents causing
contamination to the water supply?
Yes. The following is just one of a number of incidents that have
occurred in the last number of years. |
 | A resident in a small town jumped
into a shower at 5 a.m. one morning and when he got out his body
was covered with tiny blisters. " The more he rubbed it,
the worse it got, " the 60 year old resident said. "It
looked like someone took a blow torch and singed me." He
and several other residents received medical treatment at the
emergency room of the local hospital after the water system was
contaminated with sodium hydroxide, a strong caustic solution. |
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water main, broke and was being repaired. While repairing the
break one workman suffered leg burns from a chemical in the
water and required medical treatment. Investigations into the
cause of the problem led to a possible source of the
contamination from a nearby chemical company that distributes
chemicals such as sodium hydroxide. The sodium hydroxide is
brought to the plant in liquid form in bulk tanker trucks and is
transferred to a holding tank and then pumped into drums. When
the water main broke, a truck driver was adding water to the
bottom of the tanker truck instead of the top, and the sodium
hydroxide back-siphoned into the water main. |
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Are
there any regulations related to Backflow or Cross Connection
conditions?
Plumbing codes have always prohibited any connection whereby potable
and non-potable water could mix. The Canadian Plumbing Code
Committee continue to work on revising subsection 6.2
"Protection From Contamination". |
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What
Standards are available governing the manufacturer of backflow
preventing devices?
Numerous applicable standards are in place to ensure backflow
prevention devices meet acceptable standards, they include CSA,
AWWA, ASSE, ANSI, & IAPMO |
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Is
periodic testing required for reduced pressure principle backflow
preventers?
Yes, testing is a requirement of many provincial cross connection
control programs, as well as some provincial plumbing codes, and is
necessary to ensure that the valve is working properly. Test cocks
are provided on all units to facilitate field testing. Testing
information is provided by the manufacture of the backflow
prevention device |
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Should
a backflow preventer be installed in the water supply line to each
residence?
Because of the growing number of serious residential backflow cases,
many water purveyors are now requiring the installation of approved
dual check valve backflow preventers at residential water meters. |
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Will
a backflow preventer affect my water pressure?
Yes, essentially all backflow preventers cause some degree of
pressure loss but other than the reduced pressure assembly the
pressure drop is not significant. The typical pressure drop across a
reduced pressure assembly ranges from approximately 6 to 13 psi
depending the on size and make of the unit. |
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Is
a plumbing permit required when installing a backflow prevention
device?
Any plumbing alteration related to the installation of a backflow
preventer will require a plumbing permit. |
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What
type of reference material is available?
The Western Canada Water & Wastewater Cross Connection Control Manual,
CAN/CSA-B64.10-94, EPA's Cross Connection Control Manual, and AWWA's
M14 Manual are excellent reference manuals for establishing a cross
connection control program or for further information on cross
connection control. |
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What
are the five basic products used for protection of cross
connections?
The five basic products are: Air Gap, Atmospheric Vacuum, Pressure
Vacuum Breakers, Double Check Valve Assembly, Reduced Pressure
Backflow Preventers. |
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What
is an Air Gap?
Air Gap is the physical separation of the potable and non-potable
system by an air space. The vertical distance between the supply
pipe and the flood level rim should be two times the diameter of the
supply pipe, but never less that 1". Air gaps are frequently
used on wash basins and industrial processing applications. |
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Where
is an Atmospheric Vacuum Breaker used?
Atmospheric Vacuum Breakers may be used only on connections to a
non-potable system where the vacuum breaker is not subjected to back
-pressure and must be installed on the discharge side of the last
control valve and above the usage point. A Atmospheric Vacuum
Breaker it not to be used under continuous pressure. Typical
applications for an Atmospheric Vacuum Breaker are lawn sprinkler
systems and dishwashers. |
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Where
is an Hose Bibb Vacuum Breaker used?
Hose Bibb Vacuum Breaker are small inexpensive devices for hose
connections which are simply attached to sill cocks, and threaded
faucets. However, like the Atmospheric Vacuum Breaker they should
not be used under continuous pressure. Hose Bibb Vacuum Breakers are
commonly used on sill cocks, services sinks and any threaded pipe to
which a hose may be attached. |
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Where
is a Pressure Vacuum Breaker used?
Pressure Vacuum Breakers may be used as protection on connections to
all types of non-potable systems where they are not subject to
back-pressure. These units must be installed above the usage point
and may be used under continuous supply pressure. The applications
for a Pressure Vacuum Breaker are similar to the Atmospheric Vacuum
Breaker with the exception that they may be used under continuous
pressure. |
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Where
is a Double Check Valve Assembly used?
A double check valve assembly may be used as protection of all
direct connections through which any substance might enter the
potable water system in a concentration which would constitute a
nuisance or be aesthetically objectionable, such as air, steam,
food, or other material which does not constitute a health hazard.
The Double Check Valve Assembly is used where the degree hazard is
low. |
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Where
is a Reduced Pressure Principle Backflow Preventer used?
Reduced Pressure Assembly may be used on all direct connections
which may be subject to backpressure or back-siphonage, and where
there is the possibility of contamination that constitute a
potential health hazard. A Reduced Pressure Principle Backflow
Preventer is used whenever the non-potable source is more of a
contaminate such as boiler feed lines. |
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What is the
benefit of a strainer preceding a backflow preventer?
A strainer will protect the check valves of a backflow preventer
from fouling due to foreign matter and debris which may be flowing
through the line. This not only protects the valve but eliminates
nuisance fouling and subsequent maintenance and shutdown. The use of
a strainer with a water pressure reducing valve has been an accepted
practice for years.
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