Raypak VERSA 155C Operating And Installation Instructions page 16

UNITHERM GOVERNOR OPERATION
The patented Unitherm Governor is a thermostatic
mixing valve specifically designed to maintain constant
heater internal temperature between 105°-115°F de-
spite continually changing flow rates from the filter and
changing pool temperatures. This narrow range is
needed to prevent damaging condensation on the burn-
ers which will occur if the heater runs for any length of
time below 100°F. It is also needed to inhibit scale
formation in the tubes by maintaining temperatures
well below accelerated scaling temperatures.
INTERNAL AUTOMATIC BY-PASS VALVE
In addition to the Unitherm Governor, a built-in
automatic by-pass valve is provided in the in/out
header. While the Unitherm Governor responds to the
changes in water temperature in the heater, the internal
by-pass 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.
EXTERNAL AUXILIARY BYPASS VALVE
(where required)
An auxiliary bypass valve should be used when flow
rates exceed 115 GPM (usually a high performance
pump size larger than 2 HP 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 down below 50°F. It also serves to
eliminate needless pressure drop through the heater
and accompanying reduction in the flow rate to the spa
jets, etcetera.
From Heater
To Pool
Auxiliary Bypass Valve (do not use gate 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 comfort-
able to the touch. If pipe is hot, close bypass; if cold,
open bypass.
PRESSURE RELIEF VALVE INSTALLATION
To conform to local building codes, it may be
necessary to install a pressure relief valve. A 3/4"
pressure relief valve having a capacity equal to BTU/HR
output of the heater to be installed is recommended for
this appliance.
A 3/4" NPT connection is provided in the inlet/outlet
header for installation of a pressure relief valve. The
valve shall be installed in a vertical position.
PRESSURE RELIEF
Fig, # 8078.0
INLET/OUTLET HEADER
16
To Heater
VALVE
PRV DISCHARGE
CONNECTION
From Pool
Fig. # 8150.0
Fig. # 8095.0