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Help with metering setup?

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Help with metering setup?

Unread postAuthor: cfb_rolley » Sun Sep 25, 2016 9:50 pm

Hi, it's been a really long time since I've lurked around these forums, although I'm still launching vegetables and things. But, I'm hitting a dead end and need some assistance. Who better to ask than the experts?

I'm going to be setting up onboard propane or MAPP tank and metering, and this is my first venture into an advanced combustion, so I have a small handful of questions. Below is the metering setup I'm planning:
Propane metering.png
Propane metering.png (13.87 KiB) Viewed 159 times


1. I'm planning to run two inlets for the chamber for more reliable gas mixing, as the chamber is fairly long. I'll need to T off the tubes after the metering, but I'm concerned as to how this will affect the amount of gas that enters the chamber. will I need to adjust my metering calculations?

2. The bottle I'm using is this: [url]https://www.bunnings.com.au/tradeflame-tf-ultra-gas-performance-gas-mapp-replacement_p5910238][/url]. It uses a BOM fitting as far as I can tell, how can I adapt this to fit a regulator? Is there such a thing as a BOM to hose barb adaptor? If there is, I can't find one anywhere :(

3. No idea what the outlet pressure on these cylinders is, which makes it difficult to figure out what regulator I need.

4. In general, any other things I have overlooked in the plan?

Thanks very much in advance. I'll post pics of the project so far some time this week.
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Re: Help with metering setup?

Unread postAuthor: mark.f » Mon Sep 26, 2016 10:04 am

1.) If you're worried about that small of a volume, simply add it to your chamber volume, although:
  • Using a mixture fan will work much better than simply injecting in two spots, and decrease complexity and dead volume between the meter and the chamber.

2.) I made a page here which describes how I've always done it. You can also buy BOM - > 1/4" NPT adapters at specialist stores.

3.) Outlet pressure depends on temperature, but standard 120PSI max regulators work well enough. Choose a target pressure for your meter well below the tank pressure, to account for low temperatures and the decreased pressure. I usually aim for around 40-50 PSI in my meters.

4.) Not much, I'm sure you'll have fun looking at all of the examples the site has to offer... there's a lot.
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Re: Help with metering setup?

Unread postAuthor: cfb_rolley » Mon Sep 26, 2016 10:21 am

Awesome! I think you covered all bases for me. I do occasionally lurk through the showcases from time to time, and although I've been here a long time I haven't had much time for spudding over the last few years (had 2 kids +career advancement), but this combustion rig I have happening at the moment is just too much fun, even just on aerosol propellant!
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