Product Overview

Principle of Operation
The reduced pressure zone backflow preventer is composed of a body with an
inspection cover, an upstream check valve (1), a downstream check valve (2), and
a discharge valve (3). The two check valves divide three different zones, each with a
different pressure: an upstream or inlet zone (A); an intermediate zone, also known
as the reduced pressure zone (B); and a downstream or outlet zone (C). Each of
these has a test port for pressure measurement. A discharge valve (3) is located
in the lower part of the intermediate zone. The valve plug of the discharge valve
is connected to the valve stem (4) and diaphragm (5). This moving unit is pushed
upwards by the spring (6). The diaphragm (5) is the limit of the operation chamber
(D), which is connected to the upstream zone by the channel (7).
Normal flow conditions(1)
Under normal flow conditions, both check valves are open, while the pressure in
the intermediate chamber (B) is always lower that the inlet pressure by at least 2 psi
(14 kPa) due to the pressure loss caused by the check valve (1). In the operation
chamber (D), however, the pressure is the same as in the inlet zone. In this situation,
the moving unit consisting of the diaphragm (5), the valve stem (4) and the valve plug
(3) is pushed down by the thrust created by the difference in pressure acting on the
diaphragm which is greater than that of the spring (6) acting in the opposite direction.
The discharge valve is therefore held in the closed position.
No flow conditions (2)
The check valves (1) and (2) are now closed. Since the pressure in the upstream
zone, and in the operation chamber (D), is still at least 2 psi (14 kPa) higher than
the pressure in the intermediate chamber (B), the discharge valve remains closed.
Upstream pressure loss(3)
Both check valves close as the pressure upstream drops. The discharge valve
(3) opens when the difference in pressure ∆p, between the upstream and the
intermediate zones, falls reaching a value a little bit higher than 2 psi (14 kPa). Under
these conditions the action exerted by the pressure difference ∆p on the diaphragm
(5) becomes weaker than that exerted by the spring (6) and the discharge valve (3)
opens as a result. Discharge then occurs until the body of the backflow preventer
is empty. When the situation returns to normal (pressure upstream greater than
pressure downstream), the discharge valve closes and the backflow preventer is
again ready to operate.
Downstream back pressure
If the pressure in the downstream zone increases until it is greater than the upstream
pressure, the check valve (2) closes and therefore prevents water already delivered
from returning back into the mains system. If the seal of the check valve (2) is slightly
defective or there is any other defect in the backflow preventer, the device always
interrupts (disconnects) the connection between the mains system and the user
system. The backflow preventer has been designed and certified to properly function,
providing safe operation under all conditions.
Backflow:
Water flowing in the distribution piping of potable water mains systems can become polluted with undesirable and hazardous substances caused by
contaminated fluid return coming back from systems directly connected to the mains supply. This condition termed “backflow” occurs when:
a) the pressure in the mains supply is lower than the pressure in the downstream system (back syphon), such as residential domestic water, hydronic or
irrigation systems. This occurs when pipes break or when demand is very heavy by other systems connected to the same supply network;
b) the pressure in the downstream system rises (back pressure) due, for example, to water pumping from a well.
Protection can be provided by installing a backflow preventer at the inlet from the mains supply or in the internal distribution system. This will prevent
contaminated water from flowing back into potable systems.
The 574 and 575 series BA type controllable reduced pressure
zone
preventers are cer as complying with the
National and European product standards by the following
Certifying Bodies: NF - WRAS - KIWA - DVGW - SVGW - SITAC -
BELGAQUA - ACS - VA.
1 2
6
4
5
3
C
7
A
B
7
UPSTREAM DOWNSTREAM
D
(1)
The 574 and 575 series BA type controllable reduced pressure
zone
preventers are cer as complying with the
National and European product standards by the following
Certifying Bodies: NF - WRAS - KIWA - DVGW - SVGW - SITAC -
BELGAQUA - ACS - VA.
1 2
6
4
5
3
C
7
A
B
UPSTREAM DOWNSTREAM
D
(2)
The 574 and 575 series BA type controllable reduced pressure
zone
preventers are cer as complying with the
National and European product standards by the following
Certifying Bodies: NF - WRAS - KIWA - DVGW - SVGW - SITAC -
BELGAQUA - ACS - VA.
1 2
6
4
5
3
C
7
A
B
UPSTREAM DOWNSTREAM
D
(3)
6