Flame Switch Assembly

f. Non-Fire Relay. The non-fire relay is a thermal-

to either ON position. In the ON-LO position

the control switch closes a circuit to the fuel

type, time-delay relay which is a safety device

regulator to reduce fuel flow.

incorporated into the heater electrical system to stop

(4) The indicator lamp glows after the heater

fuel flow if ignition fails to occur two minutes after the

reaches

operating

temperature

and

heater is turned on. The relay heater element is

continues to glow until the heater

energized by a circuit through the power relay and the

extinguishes and the combustion chamber

flame switch in cold position. If the flame switch does

cools. The indicator lamp also provides a

not trip to hot position, the relay will break the circuit to

check of the power supply to the heater. A

the fuel regulator valve.

spring-loaded terminal on the lamp socket

g. Ignition System. The ignition system consists of

is connected to the circuit breaker, so the

a spark plug, ignition coil, condenser, and contact set

lamp glows when pressed in if the circuit

similar to automotive systems. The contact set is a

breaker button is in and power is available.

mechanical interrupter, operated by a cam collar on the

b. Flame Switch Assembly. The flame switch

combustion air motor shaft, which causes the ignition

assembly is a mechanically operated device which

coil to energize the spark plug to ignite the fuel vapor.

controls the electrical circuits during heater operation. It

The spark plug, located in the burner, creates a spark

consists of a frame supporting a microswitch and a heat-

between its electrode and the ground electrode in the

resisting tube encasing a quartz rod. The tube extends

burner base, causing fuel ignition. The ignition system

into the combustion chamber and is subjected to the

is thoroughly shielded for suppression of radio

heat resulting from combustion. The difference in

frequencies.

expansion of the metal tube and the quartz rod when

h. Limit Switch. The overheat limit switch shuts the

heated trips the microswitch. The switch automatically

heater off by breaking the primary power circuit if the

restores itself to the normal position when it cools.

temperature of the liquid rises beyond a safe limit. The

c. Preheater Assembly. The preheater assembly is

switch incorporates a manual reset button which must

an imbedded coil of resistance wire encased in a metal

be pressed to close the circuit again for further heater

sheath and mounted within the burner. It is energized

operation.

only when the heater is initially started. The preheater

i. Thermostat. The thermostat is an adjustable heat

heats the burner in preparation for the incoming fuel for

sensor which is electrically connected to the control box.

combustion. This vaporizes the fuel so that it can easily

When the liquid has attained the preset temperature, the

be ignited.

electric circuit is opened, stopping the heater operation.

d. Preheat Relay. The preheat relay is a thermal-

The circuit is closed when the liquid temperature is

type, time-delay relay which delays energizing the power

below the thermostat adjustment allowing the heating

relay that controls the ignition system, for approximately

cycle to be completed.

one minute until the preheater sufficiently heats the

j. Motor Switch. A two position switch permits

burner to allow fuel vapor to ignite.

operation of the liquid pump without the heating cycle.

e. Power Relay. The power relay is a coil operated

When the switch is in the automatic position, the

relay that controls the circuits to the combustion air

electrical circuit is connected directly to the liquid heater

blower, ignition system, and the fuel regulator valve

system. With the switch in the manual position, the

during normal heater operation. The flame switch

electrical circuit is disconnected from the liquid heater

supplies energy to the power relay coil through the

system and a circuit is completed to an electrical

preheat relay.

source, allowing the pump to circulate fluid.

AGO 5667A