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Part Number 550-142-300/0520
20
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 injec-
tion 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.
Primary/secondary (preferred)
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 13 and 14, page 21, show suggested bypass
arrangements using primary/secondary bypass piping
(preferred) for low temperature systems such as radiant
heating systems
or converted gravity systems. For
alternatives, see pages 22 through 25.
The bypass valves (items
7a and 7b) provide mixing 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 system.
Gauge
4b is optional on converted gravity systems, but
required on radiant heating systems — to display the
3d
water temperature being supplied 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/pres-
sure gauge reads at least 150°F when the system return
water is cold (approximately 60°F water temperature).
Valve adjustment
(Figures 13 and 14 on
ly)
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 tempera-
ture 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 wa-
ter from the boiler supply which mixes with return
water. Valve 7b regulates the amount of system water
flowing through the boiler secondary loop.
Water piping — low temperature systems
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