Weil-McLain CGi Series 3 Installation And Maintenance Manual page 26

CG i
GAS-FIRED wATER BOILER- sERIEs a -
Boiler Manual
4d
26
Piping - low temperature systems
BOILER-bypass piping
method
This piping method (Figure 22 or 23) is called a boiler-
bypass because part of the circulator flow is bypassed
around the boiler (through valve 7a). This method
reduces the flow rate throughout the boiler, in order to
raise the average water temperature in the boiler enough
to prevent
flue gas condensation. Boiler-bypass
piping
is effective for some boilers - including the CGi -
provided the flow rates are adjusted according to the
instructions following.
Figures 22 and 23 are alternative piping suggestions
for converted gravity (large water content or steam
systems) or radiant heating system - for use when
primary/secondary piping can't be applied (Figure 24
is another alternative, using system bypass in place of
boiler-bypass piping. Figure 24 however, is not suitable
for radiant heating applications because it does not
protect the radiant system fro m possible high water
temperature.)
Boiler-bypass piping keeps system flow rate as high as
possible and temperature drop as low as possible, help-
ing to equalize the building heat distribution.
Temperature gauges
Gauge 4a is optional if the bypass valves will be ad-
justed using cold (or room temperature) return water
to the boiler. (When setting the valves without gauge
4a
installed - using cold or room temperature water
- assmne the return water temperature to be
6Q•F.
Set
the valves
so
gauge 8 reads at least t 20"F.
Gauge 4b is optional on converted gravity systems,
but required on radiant heating systems - to display
the water temperature being supplied to the radiant
tubing.
Gauge 8 is required on all systems to assure reliable
adjustment of the bypass valves. The boiler-mounted
temperature/pressure gauge
can be used if a separate
temperature gauge is not installed
Valve adjustment
t . Start with valve 7a fully dosed and 7b fully open.
2. Gradually open valve 7a while dosing valve 7b
until the temperature at gauge
8
reads
60 °F
higher
than gauge
48. A
minimum 60°F temperature rise
through the boiler assures a low enough flow rate
and high enough average temperature to prevent
condensation even with low system return water
temperature.
3.
Valve 7a regulates the system flow rate, wllile valve
7b regulates the boiler flow rate.
4. The boiler- mounted temperature/pressure gauge
may be used in place of a separate gauge 8.
I&
WARNING!
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 shovm
in this manual provided the system supply temperature is relatively cons tent.
DO NOT
apply the methods of this manual if the system is equipped with an outdoor
reset control. Instead, provtde 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-Mcl.ain 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.
Part Number 550-142-780/0712