Weil-McLain CGi 4 Series Manual page 24

CGi
SERIES 4 — GAS-FIRED WATER BOILER —
4d
Piping — low temperature systems
Primary/secondary
bypass piping method
Primary/secondary bypass piping is preferred
because the flow rate and temperature drop in
the heating circuit(s) is determined only by the
heating circuit circulator(s). So adjustment of the
bypass valves in the boiler circuit will not cause a
change in the heating circuit rate and temperature
distribution.
Figures 20 and 21 show suggested bypass ar-
rangements using primary/secondary bypass
piping (preferred) for low temperature systems
such as radiant heating systems or converted
gravity systems. For alternatives, see pages 26
through 29.
The bypass valves (items 7a and 7b) provide mix-
ing of hot boiler outlet water with cooler system
return water — set to assure a minimum return
water temperature (at least 130°F) to the boiler.
Set the valves as explained below.
Temperature gauges
Gauge 4a is suggested, but optional on any sys-
tem.
Gauge 4b is optional on converted gravity sys-
tems, but required on radiant heating systems
— to display the water temperature being sup-
24
Boiler Manual
(preferred)
Failure to prevent low return water temperature to the boiler could cause corro-
sion 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 tem-
perature. 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.
plied to the radiant tubing.
Gauge 8 is required on all systems to assure the
return water temperature is accurately set for a
minimum of 130°F. If this gauge is not available
however, adjust the valves such that the boiler-
mounted temperature/pressure gauge reads at
least 150°F when the system return water is cold
(approximately 60°F water temperature).
Valve adjustment
(Figures 20 and 21 only)
1. Set the valves while the system is cool, setting
for the coldest expected water temperature
(usually 60°F since the system will often drop
to room temperature between cycles).
2. Start with valve 7a fully closed and 7b fully
open.
3. Gradually open valve 7a while closing valve 7b
until the temperature at gauge 8 reads 130°F
when gauge 4a reads 60°F.
4. Note that valve 7a regulates the amount of hot
water from the boiler supply which mixes with
return water. Valve 7b regulates the amount
of system water flowing through the boiler
secondary loop.
Part Number 550-142-302/0124