anyone w/similar problems on MUA?

[hvac ddc]

I've had MUA burners that had the burner orfices rust over. I would have to take a drill bit and run them into the burner to clean them out again. If they did light up, I would notice that all of the burner wasn't lit. Sometimes the gas would be enough to come across the ignitor and light and other times it fail.

[ewang]

Was the VFD installed by Greenheck?

[emcontrols]

EMC,
there is so much different stuff out there and at so many different levels!
I have leaned on this site to NEVER say NEVER cus I have always been proven wrong! All the Greenheck units I have worked on are positive gas pressure and all have either 7800 or fireye controllers, they all have pilots, some are intermittent and some are interrupted but always have a pilot.
If you said on this site, "every compressor has electricity!" you would be shot down in 30 minutes!!!!
LOL!!!!!!!!!!!

anyhow, have a good day!

Frank

Agreed, different manufactures do different things, I personally have not worked on a direct fired burner (Not indirect fired) but that doesn't mean that some manufactures refer to direct fired as actually intermitten pilot burner ignition with 100% safety shutoff. Now on boilers, AHU's gas fired, duct heaters, RTU's etc... I have worked on with pilots, and would be surprised if they didn't have one.

[jeep6275]

back to the pressure drop across the burners. this is extremely important to have set correctly.

i have had a couple greenhecks that if they were not right on they wouldnt always light. kinda finicky that way.

also if your account is not good about keeping the filters clean set you pressure drop with partially dirty filters.

when i talked to greenheck about it, they said that all units have to be field adjusted because of the variances in duct design.

hope this helps.

jeep

[relay320]

Here are some pic's I've got of what I've got. Hope it helps you out to help me out. I have been suggested to replace existing spark ignition (w/o pilot, with a direct spark ignition with xformer and pilot.). What I'm afraid of is replacing existing setup and geting call-back saying flame failure on same unit after xxxx amount spent on parts + labor!

[relay320]

A bit computer illiterate. I'll try to put pics of burner and gas train on. As you can see NO pilot.

[emcontrols]

Just curious if you confimed the building gas pressure is not fluctuating. When under a load? And if the failures occured less after increasing gas pressure on low fire.

[relay320]

guess I don't catch what your asking? Failures occured if building under load or not. main point is if building under load and not is maintaining same pressure then where does a guy go?

[emcontrols]

guess I don't catch what your asking? Failures occured if building under load or not. main point is if building under load and not is maintaining same pressure then where does a guy go?

If the inlet pressure is dropping, then the regulator upstream of gas train will need to be opened further to increase your inlet pressure to compensate for the drop. Or the regulator may malfunctioning, or the gas line undersized, or the building regulator pressure increased etc....
If it drops to low while it is running or if it is trying to light it will produce a flame failure. The inlet pressure should stay consistant wether building is under load or not.

You probably already know this but any time the flame sensor is not in the flame or weak flame (Dirty burner orphices)(Low gas pressure) or dirty sensor it will not complete the flame proof circuit.(flame proof rectification signal)

Long story short
1. inlet gas pressure must stay above nameplate minumum gas pressure when running(low fire and high fire). If it is
2.Flame proving signal must be above factory recomended minumum while running. If it is
3. replace fenwal ignition controller.

[relay320]

gas press. does stay at constant, when lit flame sig. does stay within stand. 1-2 not firm, it regulates from 1.3-2.0. The Fenwal was replaced new about 1yr. ago, also exchanged with one that know is working properly?, from a differant unit same control, just same continuous prob with this unit. Press. drop across across burn is .7?. not man spec(.65) but not enough to not light. Has anyone had issues with these fenwall controlers that have changed out to 120v ignition with xformers and solved problem?

[emcontrols]

gas press. does stay at constant, when lit flame sig. does stay within stand. 1-2 not firm, it regulates from 1.3-2.0. The Fenwal was replaced new about 1yr. ago, also exchanged with one that know is working properly?, from a differant unit same control, just same continuous prob with this unit. Press. drop across across burn is .7?. not man spec(.65) but not enough to not light. Has anyone had issues with these fenwall controlers that have changed out to 120v ignition with xformers and solved problem?

According to manufactures literature

Pressure drop across burner should be .65 you have .7 "good"
Minimum flame signal 1 microamp you have 1.3 to-2.0 "good"
It also has 10sec to prove flame at minumum of 1 micro amp, if it falls below that 1 microamp at anytime during trial or normal run operation it will fail.

What is the minimum inlet gas pressure stamped on the nameplate and what is the actual inlet gas pressure while running.

Have you actually witnessed the flame failure with your meters monitoring all of the above or is it happening when your not there?

Only reason why I ask is because everything checks out, Gas pressure dropping sporadically is very very hard to catch, easier to catch when you have all of your gas using equipment running at the same time.

[relay320]

yes I have witnessed failure to ignight. gas pressures are right I believe manufactures suggest 8-9"wg, press. drop is in frame, and is far as I know spark is adaquate. Burner is clean as can see from photo.I have turned up inlet gas press. to 8"wg as to mfg spec. The only thing I can play with is low fire ignition which there is no standard to set other than flame sense, witch I have tried to set accordingly to min low fire.

[emcontrols]

yes I have witnessed failure to ignight. gas pressures are right I believe manufactures suggest 8-9"wg, press. drop is in frame, and is far as I know spark is adaquate. Burner is clean as can see from photo.I have turned up inlet gas press. to 8"wg as to mfg spec. The only thing I can play with is low fire ignition which there is no standard to set other than flame sense, witch I have tried to set accordingly to min low fire.

When you witnessed the failure did it spark and light then fail, spark but not light and then fail or not spark and fail.

Is 8" the minimum or maximum inlet pressure on nameplate. If its minimum turn it up in between min and max(while its running).