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Part Number 550-142-300/0520
24
CGa Series 3 Gas-Fired Water Boiler — Boiler Manual
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 injection
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 return 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.
Water piping — low temperature systems (continued)
SYSTEM-bypass piping
method
This piping method (Figure 17, page 25) is called a
system-bypass because part of the circulator flow by-
passes 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 17 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 17 on radiant
heating systems
. It provides no method of regulat-
ing the water temperature provided to the system and
could result in excessive water temperature in the radi-
ant tubing.
System-bypass piping as shown in
Figure 17 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).
3d
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