Brochure

Backflow…
What is it?
Backflow? You may have heard
of it, and you may understand
some of what it involves. This
booklet will help you to under-
stand it better; exactly what it
is, and how to prevent it.
Backflow is the undesirable
reversal of the flow of water
or mixtures of water and other
undesirable substances from
any source (such as used
water, industrial fluids, gasses,
or any substance other than the
intended potable water) into
the distribution pipes of the
potable water system. There
are two types of backflow
conditions: backpressure and
backsiphonage.
Backpressure: Occurs when
the user system is at a higher
pressure than the supply water
systems allowing undesirable
substances to be “pushed”
back into the potable water
system. Some causes are:
booster pumps, potable water
system connections for boilers,
interconnection with other pip-
ing systems operating at higher
pressures, or higher elevations
in user systems such as high-
rise buildings.
One specific example of this
would be a steam heating sys-
tem with the make-up water
line piped directly into the boil-
er. The higher pressure in the
boiler could force the chemi-
cally treated boiler water back
through the make-up water
line and into the potable water
system.
Backsiphonage: Occurs when
negative or reduced pressure
exists in the supply piping
allowing undesirable sub-
stances to be “drawn” into the
potable water supply. Some
causes are:
undersized supply piping, sup-
ply line breaks, reduced supply
system pressure on the suc-
tion side of an on-line booster
pump, or sudden upstream
high demand. An example of
this is a child drinking milk with
a straw. The child “sucks” on
the straw and the milk flows
up the straw and into the
child’s mouth. What the child
is actually doing is creating a
subatmospheric pressure in
his mouth and the atmospheric
pressure (14.7psia at sea level)
is pushing down on the surface
of the milk and forcing the
milk up the straw and into the
child’s mouth.
There is one other very impor-
tant term that must be under-
stood before we can proceed.
The term is “Cross-Connection,”
and it is defined as any
actual or potential connec-
tion between a potable water
system and any other source
or system through which it
is possible to introduce into
the potable system any used
water, industrial fluid, gas, or
other substance other than the
intended potable water with
which the system is supplied.
By-pass arrangements, jumper
connections, removable sec-
tions, swivel or change-over
devices and other permanent
or temporary devices through
which, or because of which,
backflow can or may occur
are considered to be cross-
connections.
City Water
Boiler
Make-Up
Water Line
1