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CGi-4E Gas-Fired Water Boiler — Boiler Manual
28
Part Number 550-110-711/1108
Piping — low temperature systems4d
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.Valve7b will most often be full open, but may
need to be slightly closed on some low pressure drop sys-
tems 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-bypasspipingasshownin
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.
Donotapplysystem-bypasspipingifthereducedow
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. Startwithvalve7a fully closed and 7b fully open.
2. Graduallyopenvalve
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
mixedwithreturnwater.Valve7b 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
).
Boilerreturnwatertemperaturewillbeadequatelycontrolledusingthemethodsshown
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.
ContactyourWeil-McLainrepresentativeforsuggestedpipingandcontrolmethods.
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.