Part Number 550-142-302/0520
CGi
SERIES 4 — GAS-FIRED WATER BOILER —
Boiler Manual
28
Piping — low temperature systems
(continued)
4d
SYSTEM-bypass piping
method
This piping method is called a
system-bypass
because
part of the circulator flow bypasses the system (through
valve
7a
). This bypassed hot water from the boiler outlet
mixes with cooler system return water temperature in
order to provide minimum 130°F return water to the
boiler. Valve
7b
will most often be full open, but may
need to be slightly closed on some low pressure drop
systems in order to cause enough flow through valve
7a
.
Figure 24
is an alternative piping method that provides
return water temperature control for boilers installed
on
converted gravity systems
(large water content or
steam systems).
Do not
apply the piping of
Figure 24
on
radiant heat-
ing systems
. It provides no method regulating the water
temperature provided to the system and could result in
excessive water temperature in the radiant tubing.
System-bypass piping as shown in
Figure 24
can be used
with either zone valve or circulator zoning. When used
with circulator zoning however, the boiler circulator
(item
3
), must be piped as shown. It cannot be used as
one of the zoning circulators.
Do not apply system-bypass piping if the reduced flow
in the system could cause poor heat distribution. That
is, system-bypass piping reduces the flow in the system
and increases the water temperature supplied to the
system. This can cause increased heat from radiators
at the beginning of the system and reduced heat from
radiators near the end of the system.
Valve adjustment
1. Start with valve
7a
fully closed and
7b
fully open.
2. Gradually open valve
7a
while closing valve
7b
until
the temperature at gauge
8
reads at least 130°F at all
times.
3. Valve
7a
regulates the amount of boiler supply water
mixed with return water. Valve
7b
causes a pressure
drop in the system needed to balance flow through
valve
7a
and the system.
4. The valve adjustment should be done with the
system at the coldest expected temperature (60°F
for converted gravity systems or high mass radiant
systems).
Failure
to
prevent low return water temperature
to the boiler could cause corrosion
of the boiler sections or burners, resulting in severe personal injury, death or substantial
property damage.
Radiant heating system piping should include a means of
regulating the boiler return
water temperature
and the
system supply temperature
(such as provided by an
injec-
tion pumping control
).
Boiler return water temperature will be adequately controlled using the methods shown
in this manual provided the
system supply temperature
is
relatively constant.
DO NOT
apply the methods of this manual if the system is equipped with an
outdoor
reset control.
Instead,
provide controls and piping
which can
regulate the boiler re-
turn water temperature
at
no less than 130°F
regardless of system supply temperature.
Contact your Weil-McLain representative for suggested piping and control methods.
Failure
to
prevent cold return water temperature
to the boiler could cause corrosion
damage to the sections or burners, resulting in possible severe personal injury, death or
substantial property damage.
