O Potterson CF 20/35, Installation And Servicing Instrucnions, Page: 12 / 43

CIRCULATION PUMP SELECTION
The resistance through the heat exchanger when operating with a water flow r
ate producing an
11º C temperature rise at maximum boiler output is shown in
TABLE 2 . If othercontrols, such as three position valves are used in the syste
m, the resistance through them, quoted in their
manufacturer’s literature must
be taken into account. The pumpmay be fitted on either the flow or return and
MUST be wired directly to the boiler terminal block when fitted to a fully pump
ed system. It must be fitted with two isolating valveswhich are positioned as cl
ose to the pump as possible. Isolation of the valves must always leave the op
en vent unobstructed.
TABLE 2
WATER FLOW RATE BOILER RESISTANCE
With Injector Tee Without Injector Tee
litres/sec gal/min
kN/m²
in.wg
kN/m²
in.wg
20/35 .22 2.92 2.25 9.0 .30 1.2
35/50 .32 4.17 4.73 18.9 .55 2.2
FIG. 3. PRESSURE LOSS ACROSS BOILER
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