Fire Pit shut off without an empty tank

[AeroPnk]

Hi there,

I have a fire pit table that runs off of a 20lb standard grill tank. The other day we had a nice fire going and then it shut off, so I removed the tank to go get it refilled and it wasn’t empty. I weighed the tank and it still had about 7 lbs of propane in it (assuming 17lbs empty weight of the tank).

Is this normal?

 

[DAKSY]

Nope. Not normal. If there's a thermocouple in the system, it may have failed.

 

[AeroPnk]

There’s no thermocouple in the system. Strange that it has worked fine ever since. But I don’t think the tank has got that low yet.

 

[Corey]

Had the same thing happen a month or so ago. From my research... more government safety. Apparently there is a 'sensor' valve in most new propane tanks. The theory is that a spring-loaded valve detects flow out of the tank, through the regulator and to the burner/barbecue/firepit or whatever. If the flow exceeds some small 'normal' amount, it thinks a fitting has cracked or a hose has burst and snaps closed, shutting off propane at the tank valve.

The recommended fix: Turn off the appliance and turn off the propane tank. Wait at least 10 minutes. With the appliance still off, exceptionally slowly, crack the propane tank open. They mention opening the first quarter of a turn 'painfully slow'. The idea is that you let a tiny bit of propane seep out into the hose to the appliance, pressurizing it, which then allows that safety valve to open. Then once you have the propane tank open, you can turn on / light the appliance.

Shutdown should always be the reverse...shut down the appliance, then shut off propane...never shut propane first - it will allow the line to go down to zero pressure and you have to repeat the same painful start-up process again. The goal is to always keep the propane line charged with pressure.

Side note, this did not work for me - had to exchange the propane cylinder, loose the 5-6 pounds of propane I had left. Suppose I could have tried for a slightly cheaper refill, but I'd be stuck with the same flakey safety valve.

 

[AeroPnk]

Thanks, this does make sense. I wonder if this happened since I’ve got quite a large burner (150K BTU) but running it off a regular grill tank. Obviously, I not actually getting 150K BTU from that tank but I wanted a large burner for one day when I get it plumbed into the house gas line.

Since the burner is likely limited by the tank and hose capacity the tank safety feature may have “thought” there was a leak and shut itself down. I did get a new tank, I’ll see if it repeats.

thanks!

 

[Corey]

That could be. I haven't been able to dig up a lot of info on these valves... what pressure do they actually trip at? What pressure is that referenced to... tank pressure? atmosphere? is it differential or absolute, etc.

But yes, that does sound like a rather large draw for 20# cylinder. Ambient temps would also play a factor. If you're already seeing 'chilly' night time temps...40's, 50's etc - it might be hard for that small cylinder to vaporize enough liquid to keep up, especially when combined with low tank levels. If you see a frost/freezing patch on the bottom of the tank, it might be too much draw.

If the reset works - it's likely this is the case. If the reset doesn't work (my case) - it might just be a faulty or hyper-sensitive safety valve. You could possibly find an older tank, or a slightly larger 'forklift' tank, or other industrial tank without the safety valve, then just have it refilled as opposed to exchanged.