OT: Any Burner Gurus Here? Possible Maxon Valve Failure...

A few days ago I was checking the signal strength on a fire-eye module. The range was 4.00-5.50VDC, and the reading was a solid 5.2X range.
When I went to place the cover back on I accidentally pressed the 'reset' button.
NORMALLY this just shuts down both burners (there are 2 burners per actuator). Normally I just reset the plc and relite. Thirty seconds and it's done.
But.. this time.. the 'flame detected' light stayed on... on BOTH BURNERS!!! I reset the alarm, and it would come right back. I swapped the amp cards. Once inserted the flame detected light came on. I put a meter to the amp card again.. this time they read between 4.70-5.09VDC, which is really strong.. considering that the burners were supposed to be off at this time.
I thought that maybe the uv scanners had possibly 'burned in'. They're the old style (shutter-less).
However when I went to the burner I found flame. Both burners still had flame visible from the site ports. Both maxon gas valves (there are 2 in the train) were 'shut' according to the window. I tapped one of the pilot solenoids, and nothing happened.
I then shut a manual valve that was between the two maxon valves and both burners went out.

It appears that gas was passing through both 'shut' valves.

Tomorrow, when the plant has time, I'm going to clean both valve seats. My first thought is that there is build-up on the seats. This, coupled with the draft fan running at 57Hz creating a nice negative static at the burners, is why I believe that the burners stayed lit after 'shut down.'

Would like some feedback, and also some other things that might be good to look at. I'm also thinking about the springs. Maybe they need to be replaced?
These actuators have been in service since 1989. I don't believe the valve seats have ever been cleaned.

Do you have a filter in the train?, if it were I...I would replace them or get a rebuild kit

Edit: Second thought, after that amount of time and the springs being compressed for that long, then they may be getting weak?, I dont think that a build up would give you that strong of a flame signal, I would start with a rebuild kit asap

From the Maxon manual on electro mechanical valves:
http://www.maxoncorp.com/pdf/I-em-5000-808.pdf

Insurance authorities agree . . .
. . . that the safety of any industrial fuel burning installation is dependent upon well-trained operators who are able to follow instructions and to react properly in cases of emergency. Their knowledge of, and training on, the specific installation are both vital to safe operation.

Safety controls may get out of order without the operator becoming aware of it unless shutdowns result. Production-minded operators have been known to bypass faulty controls without reporting the trouble.​

Continued safe operation of any installation is then assured only if the plant management carefully develops an exact schedule for regular periodic inspection of all safety controls, insisting that it then be rigidly adhered to.​

A main gas shut-off **** should be located upstream from all other fuel train piping components and used to shut off all flow of fuel for servicing and other shutdowns.​

All safety devices should be tested at least monthly* and more often if deemed advisable. Periodic testing for tightness of manual or motorized shut-off valve closure is equally essential.​

*per NFPA 86-Appendix B-4 (1995)​

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It also states that

Maxon valves are designed to be used with clean fluids. If foreign material is present in the fuel line, it will be necessary to inspect the valve to make certain it is operating properly. abnormal opening or closing is observed, the valve should be removed from service. Contact your Maxon representative for instructions.

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If you follow the regulations for gas fired vessel inspections, leak by of the fuel shut of valves is one of the required checks.
Maxon valves are terrible, they never last more than a year in clean service, before they fail the leak test.
One trick to get a leaky valve to seat is as follows:
Squirt WD40 onto the seats and cycle the valve 40-60 times. It will then pass the leak test.

I would suggest you consider another brand of fire rated valves. We have.

If you have the ability, you might even want to look at an automatic system for proving the valves.

GM has standardized on the Dungs VDK.

The Dungs unit pressurizes the space between the blocking and safety shut-off valves and tests the valves to be sure that they can hold the pressure. The unit is set to check the valves each time the burner is run (usually after shut-down).

Thanks for all the help. There are 5 units, with a total of 18 maxon valves.
The only filtration in the stream is the y-strainer. I'll check that first. Though I've never seen that cause of valve to leak.
I'll check the seats, and talk with the plant about rebuilding/replacing them.
Since there are 18 maxon gas valves currently being used, on just the equipment I service, it might be a good idea to have a few spares.
Not sure about trying a different brand. Wouldn't be a bad idea, but this is the first time I've had this kind of failure. Then again, in the 6+ years I worked with my former company we never tested the valves themselves for leaks. We only tested the line to see if it was leaking to atmosphere.
What would be a good way to test? Would opening up burner's gas test port (1/4" barb fitting) be enough? I've never tested a valve for leaking before, but I'm very interested in learning this.



thanks again for all the feedback. Concerning valve replacement.. is there a brand that would fit the same type of physical size of the maxon's?


thanks..

Vent Stand Pipe

It is very surprising and rare that BOTH valves are leaking by. You should have a solenoid vent valve and stand pipe between the valves. Is it opening to vent when the valves are closed? Also, if it is opening, you should be smelling gas in the vacinity. I had a similiar situation several years ago with an incinerator. I thought the Maxons were leaking by, I had flame. As it turned out, the pilot regulator had gotten fouled up and was giving me more pilot flame. The extra pilot flame was being detected by the main flame fire-eye and sending the control logic nuts.

You typically hook up a piece of tubing to the barbed test port, insert the other end of the tubing into a small container of water. Open the valve on the test port and watch for bubbles, the standards list the maximum about of bubbles allowed in a defined amount of time. I don't have the spec. on hand, but I believe 10 bubbles in 60 seconds is the maximum leak rate allowed.

DenverGreg said:

It is very surprising and rare that BOTH valves are leaking by. You should have a solenoid vent valve and stand pipe between the valves. Is it opening to vent when the valves are closed? Also, if it is opening, you should be smelling gas in the vacinity. I had a similiar situation several years ago with an incinerator. I thought the Maxons were leaking by, I had flame. As it turned out, the pilot regulator had gotten fouled up and was giving me more pilot flame. The extra pilot flame was being detected by the main flame fire-eye and sending the control logic nuts.

Click to expand...

That was one of my initial concerns. However the pilot line connects to the main gas line upstream of the manual valve I had closed. My thought is that if the pilot were leaking then the burner would have stayed lit. Plus, this would mean that both pilot solenoids had failed.



I noticed that the maxon valve has an over travel setting. I'm positive that this has never been checked. It's going to be the first thing I'm going to look at today.

Is there a vent valve between the Maxons?

There is a vent valve between the two maxons. I checked the 'bug screen' end, and it looks clean.
Though due to its location it's tough to notice any gas vapours when it opens.

however... here's a quick update:

Spoke with a maxon tech. He recommended cycling the valves to clean off any accumulation. These valves aren't cycled very often, and he said that there is a possibility of condensation, which would prevent the valves from properly closing.


The tech I'm working with confirmed that he saw lingering flame in one of the burners. It seems that the only reason it flames out is because of a change in air flow within the combustion chamber itself (this is an rto). We closed the pilot line to each burner (at the manual valves).. and one of the burners still saw a strong flame signal at the module. I repeated this a number of times with the same result. I believe that it might be seeing the spark ignitor. However..
I opened up the other burner's pilot line and both burners lit. One with a closed pilot line, while the other burner's pilot line was open.
I'm now going to try a leak test on the maxon valve closest to the burners. I believe that if there are more than 15 bubbles/minute then it has failed the test. If it leaks, then both are leaking.
Quite fascinating....

It is definately an interesting problem and and probably a little fun to troubleshoot, it sounds like you are attacking the troubleshooting perfectly. Good luck and let us know what you figure out.

Here's a quick update: Yesterday I was able to perform a proper leak test on one of Maxon Valves (due to the ball valve placement I could only test the Safety Shutoff Valve, without having to do a lot of work). Since I was concerned with gas leaking through both valves and allowing the burners to stay lit, I reasoned that this test should be sufficient. If the gas doesn't get past the SSOV, then it doesn't matter the condition of the valve downstream (blocking valve), since it won't see any gas. Plus if the SSOV was good, then odds are that the other valve is good too.

The SSOV tested fine. There were No Bubbles. I repeated this test on the other 7/8 gas trains, and was happy to find that none of the valves were leaking. On one of the trains I couldn't remove the plug, but since that burner hasn't had a lingering flame alarm in the 4+ years that I've been on site, coupled with the fact that the other train on the unit tested fine, I'm not too concerned.

This leaves only one possibility: The pilot solenoid. It's an Asco Red-Hat. Due to the age of the burner there's only 1 in the train, and there's no easy way to isolate it for a test.



Thanks everyone for your feedback. I spoke at length with both Maxon and Fire Eye.

One interesting note: The fire-eye Chassis is where the lingering flame timer is located. It is supposed to be a 60 second timer. It is consistently alarming between 22-25 seconds. I've seen this happen before. But while it is a shortened alarm time, it is much longer than needed for this application.
I made the plant aware of this, and also that the chassis is still viable at this time. No sense in throwing money into replacing it, when it's not currently a problem. But, when the timer does shorten to a point where it needs to be replaced (in a few years), then the plant will already be aware of the problem. It won't be a shock.



I had a chassis timer shorten to under 12 seconds. That was a pita. lol... it was also 10 years old. Not too bad a life span.