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|Troubleshooting Direct Spark Ignition Systems|| Rating:
|Posted: Thu Feb 12th, 2009 10:27 pm||
Flame Rectification Is Vital Knowledge For Gas Heat Troubleshooters.
This article deals with flame rectification as it applies to direct spark ignition (DSI) modules. They are manufactured by a few different companies — Fenwal, Honeywell, Robertshaw, and White Rodgers, to mention a few.
The procedures for DSI flame rectification are pretty much the same for all manufacturers. It is a good idea, however, to check the specification sheets for the particular manufacturer’s equipment you are working on.
One of the primary uses for DSI systems has been on some power gas conversion burners. The initial problems with DSI systems have been eliminated by today’s technology — such things as multiple-try systems and what is called “soft lockout” (where the system will attempt several tries at ignition and, if it fails to ignite the burner, the system will shut down for 60 minutes, then go through another series of tries). This has prompted a comeback of DSI use with some manufacturers.
DSI Components And Specs
Standard DSI systems include the following components:
· A system control module that contains the electronics for regulating the system’s sequence of operation;
· A dual valve combination control (or two in-line single valve gas controls) that provides for positive gas shutoff and control of the main burner gas;
· Ignition hardware that provides for spark ignition of the main burner and monitors the presence of the main burner flame; and
· Auxiliary controls that complete the system — temperature controller, high limit control, transformer, etc.
Honeywell DSI control modules include the S825A, B, C, and D; the S87A, B, C, and D; and the S89A. All modules are for low-voltage (24 VAC nominal) application on gas-fired furnaces.
When powered by a suitable 24-VAC, 60-Hz transformer and activated by the system’s temperature controller, they perform the following functions:
1. Check for a false flame condition (short to ground) before each startup. If a false flame condition is present, the module does not allow startup.
2. Generate a potential of 30,000 V (open circuit) at the spark igniter for direct ignition of the main burner.
Note: The S89A does not include a spark generator circuit. The S89A has an internal relay for activating a separate spark generator for ignition of the main burner.
3. Open the main valve(s) of the gas control(s) to allow gas to flow to the main burner.
4. Sense the presence of a main burner flame and discontinue ignition spark. If the burner fails to ignite within the trial-for-ignition period, the module goes into safety lockout.
5. If there is a loss of power, the systems will shut down safely. Startup is initiated when power is restored.
6. If there is a loss of the main burner flame, the trial for ignition is repeated. Safety shutdown occurs if the flame is not re-established within the trial-for-ignition period.
The American National Standards Institute (ANSI) requires that all new DSI-equipped gas-fired appliances must have dual gas controls for positive shutoff of the main burner gas. This requirement can be met by using any of the following methods:
· By installing a dual-valve, “VR”-type combination gas control in the gas supply piping .
With a direct burner ignition valve , where the direct spark or hot surface systems use the same valve, and the two main valve operators work simultaneously under the control of the electronic module;
Note: For direct burner ignition, there is no pilot; leave the plug in the pilot outlet.
Ignition, Flame-Sensing Hardware
Ignition and flame-sensing hardware for DSI systems is available in several configurations:
· Separate flame sensors and spark igniters;
· Combination spark igniters and flame sensors that are mounted on a common bracket; and
· A single electrode igniter-sensor.
Generally speaking, the separate flame sensors and spark igniters are used together, or the single electrode igniter-sensor is used alone. However, some appliances use a different combination of these components; for example, an igniter-sensor for ignition and a separate flame sensor and spark igniter for flame sensing.
Whatever the combination, the system must have components, or a combination of components, for spark ignition and flame sensing.
Check Safety Lockout
1. With the system power off and the temperature controller set to call for heat, manually shut off the gas supply cock.
2. Turn the power on to energize the control module; begin spark ignition; immediately start timing.
3. Determine the number of seconds to safety lockout (spark cutoff). It should not exceed the time specified by the manufacturer.
4. After spark cutoff, manually reopen the gas supply cock. No gas should flow to the main burner.
5. Reset the system control module as described here:
· If the control module goes into safety lockout, it will remain locked out until the system is reset.
· To reset the system, adjust the temperature controller below room temperature, wait 30 seconds, and turn the temperature controller up to call for heat. Normal ignition should occur.
Final System Checkout
Start the system and observe operation through at least one complete cycle to make certain all controls are operating safely, according to the manufacturer’s specifications.
Retired US Army Refrigeration Specialist / NYC Board of Education HVAC/R (Retired)
40 Years HVAC/R service, sales,installations. a tragedy has happen to me : http://web.me.com/zenzoidman/Bobice/
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