PEERLESS PF-50 Installation, Operation & Maintenance Manual page 18

WATER PIPING AND CONTROLS
Figure 4.1: Piping Symbol Key
6. Pressure Reducing Valve: A pressure reducing valve,
such as the Bell & Gossett B-38 or a TACO #329, is
used in a hydronic system to automatically feed water
to the system whenever pressure in the system drops
below the pressure setting of the valve. These valves
should not be used on glycol systems unless close
supervision of the glycol solution is practiced.
7. Back Flow Preventer: A back flow preventer (check
valve) is required by some jurisdictions to prevent water
in the hydronic system from backing up into the city
water supply. This is especially important on systems in
which glycol solution is used as the heating medium.
8. Pressure Relief Valve: The boiler pressure relief valve
is shipped separately for field installation. It is
extremely important that this is installed on the boiler
return pipe (at the rear of the boiler).
Do not operate this appliance without installing the
pressure relief valve supplied with the boiler or one
with sufficient relieving capacity in accordance with
the ASME Rating Plate on the boiler heat exchanger.
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The valve is to be installed as shown in Figures 4.2 or
4.3. Pipe the discharge of the relief valve to within 12"
of the floor and close to a floor drain.
CAUTION
Pipe the discharge of the relief valve as close as
possible to the floor and away from high traffic areas.
Pipe the discharge to a floor drain. Failure to do so
may result in personal injury and/or property
damage.
Provide piping that is the same size or larger than the
relief valve outlet.
9. Circulator: The boiler circulator is to be sized to
overcome the pressure drop of the system while
providing the flow required by the boiler.
a. If the boiler is piped in a secondary loop of a
primary/secondary heating system, the circulator
will need only to overcome the resistance of the
boiler and any fittings in that loop.