Slant/Fin Gas Steam User Manual
Page 12
12
12. Caravan modular boiler systems are often used as a replace-
ment for old, large, inefficient boilers. Compared with older
boilers, modern steam boilers have a relatively small water
volume in the operating range. The result can be that a
normal volume of condensate return water could create high
water levels in the new modules. In most systems, the use of
a combination feed-pump and receiver will prevent flooding.
The recommended storage capacity for the receiver is shown
in Table 9. This table is based on condensate returned to the
receiver within twenty minutes of start-up. If the time required
for returning condensate is greater, a larger receiver would be
needed. Check with the fee pump manufacturer for the
correct size. The feed-pump/receiver is used to store con-
densate returned from the system, provide feed-water to the
boilers, as regulated by the pump control and add makeup
water to the system.
A balancing valve MUST be provided on the feed-pump dis-
charge line. This valve is used to adjust water volume to
prevent feed-water from entering the boilers too quickly, which
can cause water levels to “bounce”. The pump discharge
pressure must be slightly higher than the steam operating
pressure. A rate of 1 GPM per module is more than sufficient
to feed a steam Caravan system (see Table 9).
The feed pump is activated by a pump control mounted on
the equalizer drain line, (see Figure 8, page 9). When the
boiler water level drops, the pump control energizes the feed-
water pump, transferring feed-water from the receiver to the
bank of modules. On systems with more than one bank of
boilers that are isolated (valved), each bank must have a
dedicated feed-pump with a dedicated power supply, (see
Figure 11, page 11). This will prevent the operation of one
bank of boilers from interfering with another.
During operation, condensate from the heating system is
constantly being returned to the receiver. It is natural that
some steam / condensate will be lost through venting and
small, undetected leaks in the system. When the receiver
water level drops below a predetermined low level, a float
mechanism allows make-up (fresh) water to enter the receiver
and replace any water lost in the system. However, if this is
occurring frequently, the system should be checked for leaks.
The use of a water meter in the make-up line is
recommended.
Certain local codes may require a Hartford Loop. However,
the use of a Hartford Loop is otherwise not recommended
when using a feed-pump. Consult your local authorities.
WARNING: The description in this manual is for a boiler
feed-pump only. Do not use a “condensate pump” in place of
a feed-pump on a Caravan system. Unlike a feed-pump, a
condensate pump will pump water into the boilers regardless
of the boiler water level. Some systems may require the use
of condensate return pumps in distant parts of the system.
These condensate pumps must discharge into the boiler
feed-pump/receiver, not into the boilers.
13. All equipment such as steam traps and air vents in the steam
heating system should be checked for proper operation and
replaced or repaired as needed. All piping should be
checked for proper pitch.
14. It is good practice to re-pack and/or tighten the packing nuts
on all valves in the system.
Definitions of terms
• Make-up water: Fresh water introduced into the system to
compensate for evaporation, leaks, blow-down and other use of
steam or condensate.
• Condensate water: Water that has been condensed from steam
in the system.
• Feed-water: Any mixture water, both condensate and make-up, that
enters the boilers to maintain water level.
• Header: The pitched horizontal pipe connecting the modules where
steam or condensate flows to or from a bank of modules.
1
.65
13
.75
15
2
1.30
26
1.50
30
3
1.95
39
2.25
45
4
2.60
52
3.00
60
5
3.25
65
3.75
75
6*
3.90
78
4.50
90
7*
4.55
91
5.25
105
8*
5.20
104
6.00
120
9*
5.85
117
6.75
135
10*
6.50
130
7.50
150
11*
7.15
143
8.25
165
12*
7.80
156
9.00
180
13*
8.45
169
9.75
195
14*
9.10
182
10.50
210
15*
9.75
195
11.25
225
No. of
Modules
Min.
GPM
Net
Storage
Oil
Table 9: Boiler feed pump and receiver sizing
Gas
* Maximum 5 modules per bank.
On systems with more than one bank of boilers, each bank must have a
dedicated feed-pump with its own power supply. This will prevent the
operation of the one bank of boilers from interfering with another.
Min.
GPM
Net
Storage