Brochure

There are several different
types of mechanical backflow
prevention device. An alterna-
tive to a mechanical device,
is a physical separation, or air
gap. The air gap is a physi-
cal break in the system. The
different types, of mechanical
device, are used in different
situations (if there is backpres-
sure or backsiphonage) and for
different degrees of hazard.
The degree of hazard is based
on the fluid (or other substance)
that may backflow into the
supply piping system. The fluid
may be toxic or nontoxic and
could create a “non-health” or
“health” hazard.
A non-health (non-toxic) haz-
ard cross-connection is any
point on a water supply system
where a polluting substance
may come in contact with
potable water aesthetically
affecting the taste, odor or
appearance of the water, but
not hazardous to health.
A health hazard (toxic) cross-
connection is any point on a
water supply system where a
contaminating substance may
come in contact with potable
water creating an actual health
hazard, causing sickness or
death.
Double Check
Valve Assembly (DC)
The double check valve
assembly (DC) is composed of
two single, independently act-
ing check valves. The unit also
has two tightly closing, resilient
seated, shutoff valves located
at each end of the device and
four test cocks for the testing
of the check valves.
Reduced Pressure
Principal Assembly (RP)
Commonly referred to as an
RP or RPP, this device con-
sists of two independently
acting check valves, together
with an automatically operating
pressure differential relief valve
located between the two check
valves. The first check valve
reduces the supply pressure
at a predetermined amount so
that during normal flow, and
at cessation of normal flow
the pressure between the two
check valves shall be lower
than the supply pressure. If
either check valve leaks, the
relief valve will discharge to
atmosphere. This will main-
tain the pressure in the zone
between the two check valves
lower than the supply pressure.
The unit also has two, resilient
seated, shutoff valves (one
upstream and one downstream
of the checks) and properly
located test cocks for field
testing.
Pressure Vacuum
Breaker (PVB)
The pressure vacuum breaker
(PVB) is a device that contains
within a single body, a single
loaded check valve and a
loaded air opening valve which
opens to admit air whenever
the pressure within the body of
the device approaches atmo-
spheric. The device has two
tight closing, resilient seated,
shut-off valves, and it is fitted
with test cocks, appropriately
placed, for testing the device.
Dual Check Valve
(DuC)
The dual check (DuC) is a
device which has two single,
independent acting check
valves in series. It does not
have any testcocks and is gen-
erally not field tested.
Dual Check with
Atmospheric Port (DCAP)
This device has two indepen-
dent acting check valves with
a relief valve located between
the checks. The device is not
testable and should only be
used for lower degrees
of hazard.
Atmospheric Vacuum
Breaker (AVB)
An atmospheric vacuum break-
er (AVB) is a device which has
a moving element inside, which
during flow prevents water
from spilling from the device
and during cessation of flow,
drops down to provide a vent
opening. This device should
not remain under pressure for
long durations, and it cannot
have any shutoff valve down-
stream of it.
Air Gap
An air gap is a physical separa-
tion between the free flowing
discharge end of a potable
pipe line and an open or non-
pressure receiving vessel. To
have an acceptable air gap,
the end of the discharge pipe
has to be at least twice the
diameter of the pipe above the
topmost rim of the receiving
vessel, but in no case can this
distance be less than one inch.
This may seem to be the sim-
plest, most effective and least
expensive type of protection.
However, the chance for future
cross-connections, the cost of
additional pumps to pressurize
the system often makes this an
expensive protection system.
Spill-Resistant Vacuum
Breaker (SVB)
The valve shall consist of a
one-piece modular check valve
force-loaded closed and an air
inlet valve forced loaded open
to atmosphere, positioned
downstream of the check
valve, and located between
two (2) tightly closing shut-off
valves and two (2) test cocks.
Backflow Prevention
Devices
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