Fulton Hopkins (HPN) Horizontal Coil Thermal Fluid (hot oil) Heater - Manual (Page 69)

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SECTION 4
HPN-IOM-2014-0416
MAINTENANCE
4-9
Troubleshooting
 Flow Circuit/ Circulating Pump(s)
The fl ow circuit is the electrical circuit that enables the
circulating pump(s). Your thermal fl uid pump(s) will remain on
until the fl ow circuit opens to disable the pump starter or the
Off / Pump / Heat switch is turned to the “Off ” position. Items in
the fl ow circuit may include paddle type fl ow switches, a high
inlet pressure switch, a low inlet pressure switch, a high outlet
pressure switch and a diff erential pressure switch.
 LOW INLET PRESSURE SWITCH
All C-Model heaters have a Low Inlet Pressure Switch. This is
a normally open switch that closes with proper heater inlet
pressure.
The purpose of the Low Inlet Pressure Switch is primarily to
protect the heater from a low fl ow condition. The switch senses
low backpressure downstream, indicating a change in valve
position (or a dirty strainer).The Low Inlet Pressure Switch
should be set 10 psi lower than the heater inlet pressure when
the system is at operating temperature (or 50 psig; whichever
is less), assuming that none of the conditions indicated in
Table 10-A are true. Refer to Table 10-A for a tripped Low Inlet
Pressure Switch.
HIGH OUTLET PRESSURE SWITCH
All C-Model heaters have a High Outlet Pressure Switch. This is a
normally closed switch that opens with excessive heater outlet
pressure.
The purpose of the High Outlet Pressure Switch is primarily to
protect the heater from building too much pressure. Typical coil
model heaters have a maximum working pressure of 150 psi
with 100 psi safety valve(s) on the heater outlet manifold.
The setpoint should be 25 psi above the heater outlet
pressure when the system is at operating pressure and
temperature; however, at no time should the switch be set
above the safety relief valve set pressure.
Refer to Table 10-B for a tripped High Outlet Pressure Switch,
which will require the manual reset button on the switch to be
pushed.
 FLOW SWITCHES
Units older than mid-1993 have Flow Switches on the inlet of
each pipe in the coil. These are normally open switches that
close, making a micro-switch, upon fl ow establishment.
The purpose of the Flow Switch(es) is to protect the heater coil
from too high of a temperature and to protect the thermal
fl uid from exceeding its maximum fi lm temperature. Each fl ow
switch is wired in series requiring fl ow through each pipe in the
coil. Refer to Table 10-C for fl ow switch troubleshooting.
 HIGH INLET PRESSURE SWITCH
Units newer than mid-1993 have a High Inlet Pressure Switch.
This is a normally closed switch that opens with improper
heater inlet pressure.
The purpose of the High Inlet Pressure Switch is to protect the
heater from building too high of a pressure.
Typical coil model heaters have a maximum working pressure
of 150 psi with 100 psi safety valve(s) on the heater outlet
manifold. The High Inlet Pressure Switch should be set at
25 psi over the heater inlet pressure when system is cold.
At no time should the switch be set above the safety relief
valve set pressure. Reference conditions in Table 10-D for
troubleshooting.
DIFFERENTIAL PRESSURE SWITCH
Units newer than mid-1993 have a Diff erential Pressure Switch.
This is a normally open diaphragm switch that closes with a
proper heater diff erential pressure between the heater inlet
and outlet.
The purpose of the Diff erential Pressure Switch is to protect the
heater coil from too high of a temperature and to protect the
thermal fl uid from exceeding its maximum fi lm temperature.
The setpoint should be 2 - 3 psi below the published
diff erential pressure of the heater (this will vary by heater
model).
This pressure is the diff erence in pressure between the heater
inlet pressure gauge and the heater outlet pressure gauge. See
Table 10-E for troubleshooting.
 CALL FOR HEAT/BURNER INTERLOCK
The call for heat circuit is the circuit that enables burner
operation. Fulton Thermal Corporation has used a variety of
Temperature Controllers to act as the Call for Heat. Generally
these controls work in combination with a control relay. When
the Temperature Controller calls for heat, a signal is sent to the
coil of a control relay that closes a normally open set of contacts
in series with the burner circuit.
When the call for heat is met, the signal is removed and
the contacts return to their open state. Situations that may
interfere with the Call for Heat circuit are in Table 10-F. The