Keeping a Red Dragon Lit

[buzzard86]

I'm stuck on a tie down in the NE and have a Red Dragon that I use as a backup preheater (I have Reiff cylinder band and oil sump heater that I use primarily).

I've had a persistent issue with the Red Dragon not staying lit when I release the primer. In years prior, I used to return it to the factory every other season for their reasonably-priced tune up, but they have since stopped making and supporting the airplane preheaters.

I rarely use it but would like to have it functioning if necessary. I speculate that the issue is with the thermocouple, but I've tried cleaning and reinstalling with no success. Anybody have other tricks or ways to bypass the thermocouple all together?

Thanks.

Jim

 

[Bob Noel]

caveat: I'm no expert on small-engine repairs.

Why would you suspect the termocouple when it dies after you release primer?

Wouldn't it be more likely to be a problem with fuel flow?

 

[buzzard86]

caveat: I'm no expert on small-engine repairs.

Why would you suspect the termocouple when it dies after you release primer?

Wouldn't it be more likely to be a problem with fuel flow?

Not an expert here either, but I had the same problem in the past and it was thermocouple related. It works fine with the primer depressed, which by bypasses the thermocouple. Sanding the thermocouple contacts had worked in the past, but no joy this time around.

 

[Dana]

It could be the thermocouple or it could be the valve that the thermocouple activates. Does the heater have an electronic control, or is the thermocouple wired directly to the valve? You could check for voltage from the thermocouple, it's some level of millivolts depending on the thermocouple type. If it goes straight to the valve, it's more likely a "thermopile", which is essentially a bunch of thermocouples wired together to generate enough voltage to operate the valve.

 

[smv]

caveat: I'm no expert on small-engine repairs.

Why would you suspect the termocouple when it dies after you release primer?

Wouldn't it be more likely to be a problem with fuel flow?

Donno about this model, but pre-heaters typically more closely resemble a furnace than an engine. I would also immediately suspect the thermocouple.

 

[geezer]

The thermocouple may be poorly positioned in the pilot flame. The outer end should be enveloped in the hot portion of the flame, slightly above the center of the flame. Moving the heater around can jar them loose and out of place. The holders are usually fairly flimsy. Only the end 1/3 should be in the flame, if the whole bulb is heated, there is no output.

If it is positioned properly, buy and install a new one, they are very inexpensive.

 

[buzzard86]

Thanks guys, I'll try to do some more sleuthing, both with the multi-meter and also to see i I can visually determine where the thermocouple is placed. It's a very simple setup with what I think is an off-the-shelf thermocouple. Heater works fine otherwise, just frustrating and impractical to have to hold the primer open to keep it running. I don't ever leave it unattended so I've love to just bypass it altogether, but it sounds like that may not be practical.

 

[geezer]

Don't even think of bypassing it, if the flame goes out, you will blow the hanger into oblivion. Gas explosions level the house with the leak, and the ones nearby, consistently.

Thermocouples are a generic device, for pilot lights. The only difference is the length, which needs only to be approximate, and if you get one that is too long, bend an S in it or a circle. The diameter of the circle should not be less than an inch.

 

[buzzard86]

Don't even think of bypassing it, if the flame goes out, you will blow the hanger into oblivion. Gas explosions level the house with the leak, and the ones nearby, consistently.

Excellent advice... certainly don't want to blow myself or anything else up. Just wondering aloud how this setup would be different than my gas grill, which has no thermocouple.

For discussion, this Red Dragon doesn't have a pilot. Its just a piezo igniter that lights it when the primer is depressed. If I'm understanding right, I guess that the thermocouple keeps the supply valve open once it heats up. A cool thermocouple makes the heater think the flame has gone out and closes the valve, right?

 

[smv]

Excellent advice... certainly don't want to blow myself or anything else up. Just wondering aloud how this setup would be different than my gas grill, which has no thermocouple.

For discussion, this Red Dragon doesn't have a pilot. Its just a piezo igniter that lights it when the primer is depressed. If I'm understanding right, I guess that the thermocouple keeps the supply valve open once it heats up. A cool thermocouple makes the heater think the flame has gone out and closes the valve, right?

Exactly. If the flame blows out, the gas gets shut off. Also, unlike your grill, it is designed to be used mostly unattended once started. Are you going to stand there watching it while it heats your engine or are you going to do your preflight and get a cuppa? Therefore needs an 'automated' way of shutting off the gas should the flame go out... A furnace works the same way but uses the pilot light instead of the main flame as the heat source for the thermocouple. If the main gas supply is stopped for some reason and the pilot light goes out, you do NOT want the thermostat to be able to turn back on the gas until the pilot light is relit.