The Pressure Vessel
2-4
750-96 (revised 2010)
Model CB Packaged Boiler Manual
If care is not taken to insure adequate or proportional flow through the boilers, wide variations in firing rates
between the boilers can result.
In extreme cases, one boiler may be in the “high fire” position, and the other boiler or boilers may be loafing. The
net result would be that the common header water temperature to the system would not be up to the desired
point. This is an important consideration in multiple boiler installations.
2.3.1.7 — Pressure Drop Through Boiler
There will be a pressure drop of less than three feet head (1 psi - 2.31 ft. hd.) through all standard equipped
Cleaver-Brooks boilers operating in any system which has more than a 10º F temperature drop.
2.3.1.8 — Pump Location
It is recommended that the system circulating pumps take suction from the outlet connection on the boiler and
that they discharge to the system load. This puts the boiler and the expansion tank on the suction side of the
pump. This location is preferred because it decreases air entry into the system and does not impose the system
head on the boiler.
It is a common practice to install a standby system circulating pump, and these main circulating pumps are usually
located adjacent to the boilers in the boiler room.
2.3.1.9 — Pump Operation
Pumps are normally started and stopped by manual switches. It is also desirable to interlock the pump with the
burner so that the burner cannot operate unless the circulating pump is running.
2.3.1.10 — Pressure
The design of the system and the usage requirements will often dictate the pressure exerted upon the boiler.
Some systems are pressurized with air or with an inert gas, such as nitrogen. Caution must be exercised to make
sure that the proper relationship of pressure to temperature exists within the boiler so that all of the boiler’s inter-
nal surfaces are fully wetted at all times. It is for this reason that the internal boiler pressure be held to the level
shown on the chart in Figure 2-2.
When initially firing a newly installed boiler or when cutting an existing boiler into an operating system, the boiler or
boilers to be cut into operation must be pressurized equal to the system and/or other boilers prior to cutting in.
It is advisable to have a thermometer installed in the return line to indicate return water temperature. With this
determined and with the supply water temperature to the system known, the temperature differential will be estab-
lished. With knowledge of the pumping rate, the operator can easily detect any excessive load condition and take
appropriate corrective action.
Special caution must be taken to guard against any condition, or combination of conditions which might lead to
the transfer of cold water to a hot boiler or hot water to a cold boiler. This is particularly true in the case of boilers
which are operated for purposes other than supplying hot water for the normal system load (e.g., boilers equipped
with coils for domestic hot water).
It cannot be over-emphasized that rapid changes in temperature within the boiler can, and sometimes do, cause
damage.
Courtesy of: C3 Surplus LLC
Surplus Industrial Superstore
305-428-2777
https://www.c3surplus.com
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