Part number 550-142-058/0811
35
WM97+
gas
-
fired
water
boiler
—
Boiler Manual
Supplementary expansion tank, if required
— systems having volumes more than
15 gallons only
1. The boiler is equipped with an internal diaphragm-type expansion
tank, factory charged to 12 PSIG.
a. The internal tank is suitable for systems up to 15 gallons, not in-
cluding the volume of water in the boiler and its internal piping.
b. This should be adequate for finned-tube baseboard systems and
most radiant heating systems.
c. Existing expansion tanks should be left in place even if additional
expansion tank capacity is not needed for the system.
For larger volume systems, such as systems with radia-
tors or cast iron baseboard, provide an additional expan-
sion tank sufficient for the system volume
. Undersized
expansion tanks cause system water to be lost from relief valve
and make-up water to be added through fill valve. Eventual
boiler failure can result due to excessive make-up water ad-
dition.
2. If the system does not have an existing expansion tank, add a dia-
phragm or bladder-type tank, piped as in Figure 37. Always install an
automatic air vent on top of the air separator to remove residual air
from the system.
When using diaphragm or bladder tanks only — when the
boiler is installed above the system main piping, install an
automatic air vent in the top of the outgoing boiler piping
to prevent air pocketing.
Follow the expansion tank manufacturer’s sizing and applica-
tion guidelines
Existing expansion tanks
1. An existing expansion tank should be piped as in Figure 37 for dia-
phragm or bladder-type tanks, or Figure 38 for a closed-type expan-
sion tank.
DO NOT install automatic air vents on closed-type expan-
sion tank systems. Air must remain in the system and return
to the tank to provide its air cushion. An automatic air vent
would cause air to leave system, resulting in water-logging
the expansion tank.
When possible, replace an existing closed-tanks with a dia-
phragm or bladder-type expansion tank. Closed-type tanks
often cause air removal problems.
Install water piping
(continued)
Figure 37
External expansion tank piping,
diaphragm or bladder-type
Figure 38
External expansion tank piping,
closed-type expansion tank
LEGEND for Figure 37 and Figure 38
1 WM97+ boiler
3 Relief valve, supplied with boiler, field piped —
MUST be piped to boiler supply connection —
see page 10 for information
4 Relief valve piping to drain — see page 33
6 Isolation valves
8 Supplementary expansion tank, diaphragm
type, when used
9 Air separator
10 Flow/check valve (in boiler circulator)
11 Purge/drain valves
12 Boiler circulator
14 Primary/secondary by-pass valve — see
page 34 for information
15 Supplementary expansion tank, closed-type,
when used
20 Make-up water supply
23 Backflow preventer, when used
25 Pressure reducing valve, when used
26 Internal expansion tank, diaphragm-type
27 Quick-fill valve, when used
28 DHW boiler water supply connection, when
used — see page 11 for information
29 DHW boiler water return connection, when
used — see page 11 for information
30 Pressure/temperature gauge, supplied with
boiler, field piped
