Low Water Cutoff - RBI FUTERA XLF Series Installation And Operation Instructions Manual

Table 7 Temperature Rise Table
Model ΔT = 20 o
Number
Flow Rate Pres. Drop
GPM
2500 217.5
3000 261.0
3500 304.5*
4000 NA
Model ΔT = 25 o
Number
Flow Rate Pres. Drop
GPM
2500 174.0
3000 208.8
3500 243.6
4000 278.4 *
o
Model ΔT = 30
Number
Flow Rate Pres. Drop
GPM
2500 145.0
3000 174.0
3500 203.0
4000 232.0
Model ΔT = 35 o
Number
Flow Rate Pres. Drop
GPM
2500 124.3
3000 149.1
3500 174.0
4000 198.9
* This fl ow rate exceeds the recommended maximum for a boiler with
a standard copper heat exchanger. Use a greater temperature rise or
consult manufacturer. Consider a cupro-nickel heat exchanger, because
its maximum fl ow rate is 315 GPM.

Low water cutoff

If a boiler is installed above any radiation elements it must be fi tt ed
with a low water cutoff device.
Refer to the wiring diagram supplied with the boiler/water heater for
proper wiring connections.
Expansion tank and air separator
An expansion tank or other means to control thermal expansion
must be installed in the heating system. An expansion tank must be
installed close to the boiler on the suction side of the pump. An air
scoop and automatic air vent must also be installed to eliminate air
trapped in the system.
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F F F Finned copper tube gas boilers & water heaters – Boiler Manual d
F ΔT = 11.1 o C
Flow Rate Pres. Drop
Ft L/s kPa
10.05 13.7 29.6
15.20 16.5 44.8
20.26 19.2* 59.7
NA NA NA
F ΔT = 13.9 o C
Flow Rate Pres. Drop
Ft L/s kPa
6.45 11.0 19.0
9.73 13.2 28.7
13.40 15.4 39.5
17.30 17.6* 51.0
o
F ΔT = 16.7 C
Flow Rate Pres. Drop
Ft L/s kPa
3.71 9.1 10.9
6.75 11.0 19.9
9.56 12.8 28.2
12.00 14.6 35.4
F ΔT = 19.4 o C
Flow Rate Pres. Drop
Ft L/s kPa
2.79 7.8 8.2
4.65 9.4 13.7
7.19 10.9 21.2
10.48 12.5 30.9
b b l & h
Primary/secondary piping
Boilers connected to heating systems using zone valves, zone pumps,
or systems that have excessive fl ow rates or return water temperatures
o o
less than 140 F, 60 C must be isolated from these systems to protect
the boiler.
Variable water fl ows
Figure 10, shows a typical primary/secondary piping system.
A dedicated pump is used to maintain a constant water flow
through the boiler. Th is boiler pump is sized to overcome the head
loss of the boiler and near-boiler piping system while supplying the
fl ow rate required to maintain the desired temperature rise across
the boiler heat exchanger. Th e system pump is sized to provide the
required fl ow to the heating system. Th e boiler piping connections
to the heating system piping must be a maximum 6 pipe diameters
between centers to ensure zero pressure drop in the primary system.
Low return water temperatures
To prevent the problems associated with condensation of the
products of combustion due to low return water temperatures a
primary/secondary piping system with a bypass and bypass valve
must be installed, see Figures 11 and 12. Th e bypass system must be
sized the same as the secondary piping. Th e primary and secondary
pumps should be sized to provide the required fl ow through each
system. Th e boiler piping connections to the heating system piping
must be a maximum 6 pipe diameters between centers to ensure zero
pressure drop in the primary system.
Multiple boiler systems
Systems using multiple boilers can also be installed using a primary/
secondary manifold system, Figure 13.
Piping for use with cooling units
The boiler, when used in connection with a refrigeration
system, must be installed so the chilled medium is piped
in parallel with the boiler. Appropriate valves must be used to prevent
the chilled water from entering the boiler.
When a boiler is connected to a heating coil that may be exposed
to refrigerated air from an air handling device, the piping system
must be equipped with fl ow-control valves or some other automatic
means of preventing gravity circulation of the boiler water during the
cooling cycle.
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