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Fig. 29: Mechanical Modulating Valve
M
ODULATING VALVES
W/ BUILT-IN REGULATOR
Fig. 28: Mechanical Modulating Valve Location
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The design uses a motorized valve which varies posi-
tion based upon an external controller that
communicates with the gas valve actuator, through a
3-wire 0-135 ohm wiper circuit. Minimum fire is 20%
of rate. The actuator runs on 120V power, and takes
26 seconds to go from fully closed to fully open.
Raypak offers a single-boiler digital controller which
drives the actuator; see controller options B-40 and
B-41 (includes outdoor reset). For systems with mul-
tiple boilers, see controller options B-45 through
B-47. For a field-supplied controller with a 4-20 mA
signal, see option B-35.
-
Fig. 30: Single Stage Tankstat
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The boiler will fire at low fire when there is closure
across the stage 1 contacts. Thereafter, it will fire at
high fire when there is closure across the stage 2
contacts. Numerous staged controllers are available.
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The boiler will fire at full fire when there is closure
across the TH contacts. Numerous mechanical
staged controllers are available (see Fig. 37), as well
as digital controllers offering additional features. A
typical wiring diagram for a mid-size H4 unit is shown
on page 35; this basic layout applies to most other
firing modes as well.
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The boiler will fire at lowest setting when there is clo-
sure across the stage 1 contacts. Thereafter, it will
fire at increasing rates when there is closure across
the contacts for additional stages. Loss of closure
across stage 1 will shut down the entire boiler imme-
diately. Numerous digital controllers are available.
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Connections for Tankstats in WH modes are shown in
Figs. 30 and 31.