Weil-McLain CGi Series 3 Installation And Maintenance Manual page 28

CG i
GAS-FIRED wATER BOILER- sERIEs a -
Boiler Manual
4d
28
Piping - low temperature systems
SYSTEM-bypass piping
method
This piping method is called a system-bypass because
part of the circulator flow bypasses the system (thro ugh
valve 7a). This bypassed hot water fro m 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 dosed on some low pressure drop sys-
tems in order to cause enough flow thro ugh valve 7a.
Figure 24 is an alternative piping method that provides
return water temperature control for boilers installed
o n 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
o ne 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.
Va lve adj ustment
I. 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 at least 130°F at all
times.
3. Valve 7a regulates the amountofboiler 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 (600F
for converted gravity systems or high mass radiant
systems).
I&
WARNING!
Failure to prevent low return water temperature to the boiler could cause corrosion
of the boiler sections o r burners, resulting in severe personal injury, death or substantial
property damage.
Radiant heating system piping should in d ude a means of regulating the boller 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 boller 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 o r burners, resulting in possible severe personal injury, death o r
substantial property dan1age.
Part Number 550-142-780/0712