Peace Flame

Hi

I could do with some design help, please.

I'm tasked with producing a propane fired peace flame for the village. The enclosure will hold two 3.9kg propane tanks with an automatic changeover valve that switches to a full cylinder when the first is empty. The valve incorporates a 37mb regulator. We have been given a ruby pilot jet from a portable gas heater.

When fed from the 37mb regulator, the flame from the pilot is too large and will consume too much gas. So I produced a manifold with a tapered screw to throttle the gas flow and reduce the flame. Here's the drawing of the manifold:

The problem is that the adjuster has to be screwed in tight to get the flame down to what it needs to be. I was disappointed that screwing the screw in tight does not completely shut off the gas flow and it is very sensitive. Screwed fully in, here's the flame produced:

The flame size is about right but I want a finer adjustment. Can anyone suggest a better design for the throttle that will completely shut off the gas and allow fine adjustment at the very low pressures and flows pertaining?

Thanks!

These are very effective, Glyn : **LINK**

https://bullfinch-gas.co.uk/regulators/bullfinch-regulators/variable-tinyreg-for-propane-0-1-bar-detail

MichaelG.

As Michael has indicated, you do need a pressure regulated output.

He has got a low pressure 37mbar regulator, presume that is being used before the adjuster

I find the small regulators for camping gas cylinders give quite fine adjustment, that is what I'm using to control this flame

Edited By JasonB on 13/08/2018 16:15:25

Thanks for the replies. Following Jason's suggestion, I took the burner off a butane stove and lit the jet. The control knob is just what I want. But how to get it apart to see how it works without wrecking my stove?

I assume the valve is seeing the full vapour pressure of the butane (about 30 psi or 2000mb).

Edited By Glyn Davies on 13/08/2018 16:55:05

Have you or the village looked into the legal and insurance implications of using this in a public place? I'm sure you can build it safely to a good standard, but unless you are a qualified gas engineer it is probably best avoided. Just saying. .

You're using an M8 adjusting screw! I wouldn't use that to regulate the Niagra falls. (model)

You want to look at the throttles for a model aeroplane engine which use a fine needle and a fine thread.

Get yourself two fine sewing needles one the smallest you can and the next a bit bigger, but not darning needle size. Make the small one into a small drill by grinding off the end and then grinding it into an elongated chisel shape.
Drill your brass valve seat almost through with the smallest drill you can find and not break. Then finish off the last 20 thou (half mm) with the needle.
Thread the body something like M2.5 or 6BA and drill a screw so that you can fit your larger needle in it.
The gas is of course going though the hole not across it as you have in your prototype and the needle is downstream so thread sealing is less of an issue.

The auto-changeover might also be problematic as the pressure from a propane cylinder hardly changes until it's empty as the liquid evaporates. Wouldn't it be easier to just connect the cylinders in parallel with both valves open?

One thing that does affect the pressure is temperature, as the latent heat of evaporation has to be supplied by ambient heat. Propane is I believe reputed to be more affected than butane. I guess if you have a pressure regulator that should avoid problems except at very low temperatures when the cylinder pressure may be too low to regulate. Even in the UK I believe that this can make winter caravanning problematic.

You will also need I think a flame failure device so that if the flame does go out the gas flow is stopped - I recall that some of these used to have a sensitive solenoid operated by a thermocouple, I don't know if these are available and suitable for propane.

Ages ago I did a little bit of consulting for British Gas Research on microprocessor controlled gas cookers. As gas cookers are popular because they still work in a power cut, there was interest in having something not needing mains. One idea we had was to use the pilot light to generate some electric power using a thermopile, question was whether a pilot could generate enough power. It turned out the the relevant BS required that the minimum pilot light had to dissipate the BThU equivalent of 250 W! Even if we could only get 1% efficiency we could have 5 volts at 500 mA for our electronics! Shortly after that pilot lights were banned in new appliances - 10 million homes x 250 watts being 2.5 gigawatts! We looked at all kinds of ideas to generate the power, my favourite being a stirling engine.

May be easier to just make an adaptor from your change over valve to take a camping regulator and from that to your burner. Thread on the end of the hose is M7 x 0.75. This is what I was using

Why do you need an automatic change over? You could just run the two bottles in parallel if you want a longer running time.

Auto change over is easy once you get used to how long a cylinder lasts you just go and swap the empty one and the flame never goes out. If you have two together you will either have to sit there waiting for them to empty, gas will run out or change before all the gas is used. Latest ones will even tell you when the bottle is empty.

I've fitted a few kitchens where there was no mains gas and used a similar setup but with 47kg bottles for the hob.

With such small gas usage I doubt icing up of the bottles will be an issue, don't think you would even notice a temp drop, different if you had a 20Kw burner on the end

Edited By JasonB on 13/08/2018 18:45:43

Use weight, not temperature, to trigger the changeover.