I've been prototyping a forced air propane burner over the winter, getting it dialed in and working one step at a time. Only testing the burner outside of the furnace, for now. Decided to try the 130 cfm boat bilge blower w/ motor speed controller and 12V DC power supply seen in another post... which is working quite well BTW. Being a boiler operator/ mechanic most of my career operating NG boilers I have to wonder what would happen if I lost household 120V power, the 12V DC power unit, motor speed controller or the blower motor. Typical propane pressure during testing has been 10-12 PSI w/ regulator, 1/4 turn ball valve for quick shut off, needle valve for fine tuning and MIG tip orifice. If a blower failure of any kind, there would still be 10-12 PSI of propane being introduced to the furnace, the flame would fail but what about the 10-12 PSI being introduced to the furnace (most likely cherry hot)? I could see a possible hazardous situation w/ gas accumulating in the furnace and finding any air supply to reignite, even back through the forced air supply. Boilers have draft sensors that would trip the burner out if forced air flow was lost, only experienced it once when the drive belts on the forced air blower crapped the bed. I was totally 'eyes on' when I operated boilers vs the just wait for an alarm guy, but there could be times I walk away from this furnace even for a minute or two. Am I overthinking this or is there a way around this scenario? Thoughts? Discuss.
Battery, with diode between battery and power supply. When the power goes, you've still got power to your motor (for a while, at least). 2) solenoid valve held open by the power supply. Power goes, gas valve closes.
That's one of the reasons everyone here would tell you not to leave a lit furnace unattended. If you're really worried about it, dennis has got your answer.
I don't believe you're overthinking it as I had a blower failure during a cast iron melt over the summer. I was on my second heat using a 1.0 gph Delevan siphon burning mostly diesel. I had my compressor at about 10 psi and fuel at about 20psi when the blower quit. So I was still at least getting some air in there. I had orange yellow flame at least 4ft out my exhaust, 12" all around my lid seal, and out the back of my burner before I got the fuel shut down. Lots of black smoke. So yeah, blower failure is a distinct possibility. I know you're talking gas. A cold furnace and a hot furnace would almost certainly behave differently. At least with a hot furnace you would have plenty of heat for sustained ignition and by the time it hit the vent hole you'd probably get a flame geyser. I doubt there would be enough gas buildup to give you much more than a whoosh on reignition. A cold furnace full of gas could be a different matter, but given the size of our typical furnaces I doubt you get much more than a gunshot and brown shorts. None of this is desirable so you could use dennis' suggestions above, or be Johnny on the spot. Pete
You are correct sir. If I'd walk the 20 feet to behind my garage to take a leak or go in the shop to fetch a tool, that's fairly close and less than a minute. Going in the house for a cold snack could be similar. I highly doubt I'd shut down every time as there could be many. Gotta wonder though how many casters here actually shut down when walking away for a minute or so, be honest here.
That was my first thought but would only cover power loss. If the motor speed controller or blower motor shit the bed there wouldn't be any indication other than through observation. The 12VDC power supply, motor speed controller and blower appear to be general duty but not what I would call commercial quality. Maybe the bounce house blowers are a step above these. Blow driers seem to be popular here also, so the bilge blower seems to be middle ground as I see it. I've used 12-36VDC NC solenoid valves before so familiar w/ them, pneumatic applications tho. Only asking because I don't wanna be 'that guy' who detonates a furnace in the carport, if that's even possible, I dunno.
I've had one person's furnace scare the <expletives> out of me when it pauses and then "thumps." If it's just the furnace thumping, you'd need to have worse PTSD than mine to really worry about it. If the carport loads up with well-mixed propane, though...
So, got to thinkin' and looked up air flow switches for residential furnaces, ductwork and power vents for gas fired water heaters. Adjustable range be more better. 24VAC appears common and probably cheaper than 120VAC. Air flow switch in circuit to control gas rated NC solenoid valve. This sounds doable. After 4AM now, callin' it a night.
Wasn't there a video on this site of a furnace lid thumping, lifting or popping off not that long ago? Don't remember all the details here. I wouldn't know where to start that search. But yea, I don't wanna be that guy.
You have to set out to make a propane furnace light with a bang, the standard procedure is to get a sheet of newspaper and crumple it up, stuff it into the furnace and light it, then shut the lid, turn on the gas and ease open the air valve if using forced air. It will light with a whoomp! and blow burning newspaper embers into the air. You could fit a "normally open" spring loaded butterfly valve arranged so that if power fails, the valve opens the air pipe to the outside and allows enough convection air into the hot furnace to keep a rich sooty flame burning without forced air. A similar power fail cut off valve on the gas line would cut the gas too.
What's a little pee or skidmark stained drawers among friends??? It was windy at my house tonight and my wife went out to relight the gas lanterns. As I watched her do it on the cameras, I was hoping she would remember to BLOW some fresh air in there before relighting them. All I could think of was THIS! Ya still owe me a hot tub ya IDIOT!
search "sail switch" they can be set up to shut off the gas if you loose sufficient air flow , you have to wire them with a bypass so you can start the burner if your a BT you can figure it out V/r HT1
That looks like a very simple set-up, it would fairly easy to repurpose this type of simple micro limit switch to do that.
Thanks guys. I'll take a look at sail switches and how to adjust and mount them. Looking at this type currently for ease of install: Robertshaw, comes with several springs for range and is adjustable as well. Ordered a digital manometer to bench test the burner first, then to order a switch in range. Since I retired I cannot borrow the 'cool tools' from work anymore. Likely will have to tune the switch in the furnace. 24VAC and 110VAC gas rated solenoid valves are relatively cheap also. Don't mind spending time and money on projects like these, it's way cheaper than my old hobbies like building project vehicles.
I don't turn my back on it but still food for thought...thanks. Using an inducer motor, has the pressure port for those switches already in place. Al
When my furnace is running, I don't shut down it when I just walk indoors or into the shed to pick up something like a tool or a drink. It usually lasts less than a minute. TO: When the blower fails, does the gas flame really go out ? At my furnace, never, it just gives a, slightly sooting, yellow flame. Turn on the blower and a dull thud sounds and it runs again. In a cold furnace, it is harder to keep the flame on as the blower tends to blow out the flames against the cold furnace walls. But that is over after a few minutes.
I'm running forced air propane. Once it's lite and the furnace is hot it doesn't really go out even with the blower not running. It's not stable or hot but it's not going to be an explosion hazard. That is unless you take off for a couple of hours with it unattended.
