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Unitherm Governor Operation
CAUTION: The patented Unitherm Governor is
A
a thermostatic mixing valve specifically designed to
maintain constant heater internal temperature between
105°F (41°C) and 115°F (46°C) despite continually
changing flow rates from the filter and changing pool
temperatures. This narrow range is needed to prevent
damaging condensation on the burners which will
occur if the heater runs for any length of time below
100°F (38°C). It is also needed to inhibit scale formation
in the tubes by maintaining temperatures well below
accelerated scaling temperatures.
UNITHERM
GOVERNOR
Figure 18. Unitherm Governor - Bronze
Internal Automatic Bypass Valve
In addition to the Unitherm Governor, a built-in automatic
bypass valve is provided in the In/Out header. While the
Unitherm Governor responds to the changes in water
temperature in the heater, the internal bypass valve
automatically responds to changes in water pressure in the
piping system. Proper amount of water flow is maintained
through the heater under varying pressures dictated by the
conditions of the pump and filter.
BYPASS DISC
SPRING
"YELLOW" COLOR - 268A
"GREEN" COLOR - 408A
Figure 19. Internal Automatic Bypass Valve - Bronze
NOTE: The Unitherm Governor and Bypass Valve Assy
are not individually replaced components on ASME units.
If either needs to be replaced, the entire UG/Bypass assy
must be replaced. The "yellow" color spring is used on
model 268A. The "green" color spring is used on model
408A.
APPROVED
UG/BYPASS ASSY
F10642-2
UG/BYPASS ASSY
F10642-4
UNCONTROLLED DOCUMENT IF PRINTED
External Auxiliary Bypass Valve
Where Required - An auxiliary bypass valve should be
used when flow rates exceed 100 GPM (378 lpm). Usually
a high-performance pump size larger than two horsepower
will exceed this flow rate. This valve is required to
complement the function of the automatic bypass valve,
particularly when starting the heater in winter or early
spring when the spa or pool temperature is below 50°F
(10°C). It also serves to eliminate needless pressure drop
through the heater and accompanying reduction in the flow
rate to the spa jets, etc.
FROM HEATER
TO POOL/SPA
BYPASS VALVE
Do not use gate valve.
Figure 20. Auxiliary Bypass Valve
Auxiliary Bypass Valve Adjustment
To set bypass, with clean filter, adjustment is made by
feeling the inlet and outlet pipes at the heater. Outlet pipes
should be slightly warmer than inlet and comfortable to the
touch. If pipe is hot, close bypass; if cold, open bypass.
FULL PORT
BALL VALVE
OR GLOBE
VALVE
FROM POOL/SPA
17
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