25
®
DESCRIPTION OF FUNCTIONS OF OPERATING CONTROLS
1.
Limit Switches:
These are generally pressure, water level or temperature activated. There are two
types which are:
a. Recycle - when it is desired to start the burner or a call for heat is present, the limit switch
closes causing the burner start-up sequence to begin. When it is desired to stop the burner or the
setpoint has been satisfied, the limit switch opens causing the burner to stop. The recycle limit is
connected between terminal 4 and 5.
b. Non-Recycle/Lockout -when it is necessary to stop the burner when the limit switch opens and
prevent it from starting until both the limit switch recloses and the manual reset is activated. The
non-recycle limit is connected between terminals 4 and 14.
2.
Proof of Closure Interlock:
This is generally an integral switch mounted on the main fuel valve
and activated by the valve stem. It is connected between Terminal 4 & 12 when burner is idle.
The POC switch interlock prevents a burner start-up if the valve stem is not in the "valve closed"
position. This interlock must remain closed while in STANDBY and until the start of PTFI.
3.
Purge Interlock:
Generally a firing rate motor linkage position switch or a differential air-pres-
sure switch, that proves a maximum purge air flow rate. It is connected between Terminals 8 and
9. The purge interlock proves that the air damper is fully open and purge air flow rate is at maxi-
mum during the purge.
3.
Running Interlocks:
These generally are high and low fuel pressure switches, oil temperature
switches, atomizing media pressure switches, and excess smoke density controls. These inter-
locks prove proper conditions for normal operation of the burner.
