TYPICAL
START UP SEQUENCE
The sequence represented on this page is typical of over 95% of the equipment that we build. Actual options installed on your heater may cause the equipment you are servicing to deviate slightly from the sequence shown however, the basic requirements to provide safe and proper startup of fired equipment remain the same therefore the intent of the sequence steps will remain the same.
FIGURE 1.1
REFER TO FIGURE 1.1 for a timeline which represents the following steps.
STEP 1 - Standby - Provided that the control panel has been powered and all of the alarms have been cleared. The heater is now ready and waiting the operator to initiate a heater start. Some of the alarms are active as shown at the bottom of Fig. 1.1. The heater may remain in this condition indefinitely, this step is not timed.
STEP 2 - Heater Start - This step is initiated by the plant control system or by the operator placing the control panel switch in the run position, or pressing the start push-button. (Some systems may start this step automatically when panel power is on and the alarms are cleared). The first noticeable action is to energize the circuit which provides a signal to the motor starter(s), this will start the blower(s) to provide air for ‘Pre-Purge’ and for combustion. Ten seconds later combustion air alarms become active. The second noticeable action is the movement of the firing control linkage toward the Max position. This step takes no longer than 30 seconds and ends when the control linkage reaches high fire.
STEP 3 - Pre-Purge - at this stage of operation the blower(s) are pushing air into the heater cabin or firetube. Typically both the air and fuel control valves are open, however the fuel block valves are closed, this arrangement allows the maximum air flow without any fuel flow into the combustion chamber of the heater. The control linkage will remain at high fire position until the Pre-Purge Timer is complete. This timer is typically 90 to 120 seconds. (The timer on most systems will not count up if the low fire start switch does not open to signify that the control valve has moved to open).
STEP 4 - Pre-Purge Complete - This step begins when the timer for step 3 is complete. The blower(s) will remain on as the control linkage returns to the Min (Low Fire) position. Steps 2 thru 4 have provided a safe environment within the heater cabin or firetube prior to ignition. This step takes no longer than 30 seconds and ends when the control linkage reaches low fire.
STEP 5 - Ignition - The LFS-01 switch will confirm that the purging steps are over and will initiate the ignition of the heater. The pilot gas solenoid valve(s) will open and the ignition transformer(s) will provide the spark ignitor(s) with 10 seconds of continuous sparking activity. (The low fire start switch will be a limit switch capable of determining and closing its contacts when the control valve has returned to the minimum firing position or it may be a pressure switch monitoring air pressure downstream of the air control damper the switch will be is wired to close when the air pressure within the burner is low).
STEP 6 - Standing Pilot - At the end of the 10 second ignition period, if flame is confirmed by the UV detection device on the burner(s), the pilot gas valve will remain open and the control system will begin a 5 second timer before moving on to step 7. This 5 seconds will insure that the a stable pilot flame has indeed been established and can maintain itself. If the burner(s) does not appear to have a pilot flame, the pilot gas valve will close and the control system will return to step 2 and will flush any unburned pilot gas from the heater cabin by repeating the purging steps. If the pilot(s) can not be established within 5 attempts the heater will lockout and indicate which burner is failing to achieve pilot ignition.
STEP 7 - Main Flame Establishing - With a confirmed pilot flame, the control system will open the fuel gas block valve(s). On a system with two block valves and vent valve located between, the fuel gas vent valve will be the first to act by closing, immediately following will be the opening of the fuel gas block valves allowing fuel gas to travel toward the fuel control valve(s). Within the 10 seconds following the opening of the block valves a relay will energize and complete the 4-20mA control circuit enabling the TIC to control the throttle of the heater. (On systems using pneumatic controls a 3-way solenoid is used to route the 3-15psi to the control actuator).
STEP 8 - Fully Operational - The end of step 7 marks the end of the start up sequence the heater is now fully operational. The Temperature Controller will move the firing control linkage (by electronic or pneumatic means) as required to achieve the set-point input to it. This step is not timed and will continue until the operator or plant control system stops the heating cycle or an alarm condition occurs.
STEP 9 - Back to Standby - The end of the heat cycle or any alarm will take the control system to this step. The following events will occur as the heater shuts down. Pilot and fuel gas block valves will shut, any fuel gas vent valve will open, the firing control linkage will return to the Min position, the burner blowers will remain on for 5 minutes past the shutdown to cool the burner parts. If the shutdown was caused by an alarm, one of the alarm lamps should be indicating why the heater has shutdown. This step is not timed. As long as all alarms are clear the heater will be ready and waiting for the operator or plant control system to initiate a heater start as in step 1. For all intents and purposes the system has returned to step 1.
ALL ALARMS ARE CLEAR BUT HEATER DOES NOT INITIATE STEP 2
HEATER PRE-PURGE BEGINS BUT DOES NOT END
HEATER PRE-PURGE STARTS AND ENDS BUT SYSTEM DOES NOT FOLLOW THROUGH
WITH IGNITION
SYSTEM COMPLETES PURGE AND TRYS TO IGNITE BUT FAILS TO LIGHT THE PILOT
PILOT LIGHTS, MAIN FUEL VALVE OPEN BUT FLAME GOES OUT AND UNIT SHUTS DOWN
HEATER STARTS BUT DOES NOT MAINTAIN TEMPERATURE PROPERLY
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