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Fueling problems (manometer)

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Fueling problems (manometer)

Unread postAuthor: CS » Wed Jan 23, 2013 9:02 am

So I fill the manometer to a water column difference of 14.8" (adjusted for elevation). Close the ball valve to the meter, click the sparker, and nothing. I've tried shaking it (mixing), adjusting the spark gap (always sparks when chamber open), clear chamber with compressed air every time to make sure propane isn't left behind.

Thinking it might be a mix problem I tried a 2x hybrid mix. 29.6" difference, 13 ish psi air. Nothing.

The ignitor is not picture, it is a BBQ sparker.

Electrode gap is not shown, its the all thread sticking out the back, and bent to points in the chamber.
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Attachments
IMAG1059.jpg
Overview
IMAG1060.jpg
Electrodes, part of fuel meter
IMAG1065.jpg
Burst disk, m/f adapter,2 rubber washers
IMAG1062.jpg
Overview with manometer
IMAG1063.jpg
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 23, 2013 9:07 am

Haven't checked your math but what is your spark gap? In my experience they need to be a fraction of a millimetre for hybrid ignition with piezos, even though 2x isn't much.
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Unread postAuthor: CS » Wed Jan 23, 2013 9:13 am

I'd say 1 mil. I did do a lot of attempts at 1x for the issue of my sparker. Need to buy a 9 volt and I can try to fire with the stun gun.
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 23, 2013 9:16 am

I would make it as small as possible, literally paper-thin, and also make sure the birst disk isn't leaking as even a small leak will throw the mix off completely.
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Unread postAuthor: jrrdw » Wed Jan 23, 2013 9:34 am

I'll take electrode insulation all the way to the point under fueled conditions for 500 Alex.
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Unread postAuthor: CS » Wed Jan 23, 2013 9:34 am

Fixed 4 leaks already: burst disk (two rubber washers absorbed the mis alignment over just one), teflon tape on each electrode, and tightend the 6" brass nipple.

The quick connect needs to be elimnated it leaks slowly. I lose a 1 psi in about 30 seconds. A good thing in way so I can transverse different mixes. I've over shot the called amount in hopes at a certain point the mix will cross into an ignitable mix.

Damn maddening. Stun gun, and fixing the quick connect are in order.
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Unread postAuthor: MrCrowley » Thu Jan 24, 2013 7:04 pm

How accurate is your gauge? I can't tell from the photos what it reads to. You definitely want a gauge that reads something like 0-15PSI for manometric metering as a 150PSI gauge with an error of 1.5% F.S. could be either side of the gauge reading by a couple of PSI.

Apart from that, you might have difficulty using manometric metering in a smallish cannon at low mixes. I don't believe I've tried it below 4x or 5x on my 500ml hybrid.
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Unread postAuthor: CS » Fri Jan 25, 2013 5:24 am

The gauge pictured was 0-160psi. Now I got a 0-60psi (lowest range I could find locally). Which will work for 2-5x mixes nicely.

Good news, got it to fire yesterday. Bad news, once out of ~20 tries. And didn't close the ball valve and now air leaks out of the bike pump somewhere... slowly. Got a plan to fix that though.

The bike pump doesn't have a good seal on it, so idea is have a bike pump-> schrader valve -> buffer tank -> blowgun -> where the schrader valve used to be.

Got a long ways to go to come up with a repeatable design so I can have multiple cartridges...

I love how problems are never anticipated, never would have guessed I'd be fixing leaks to get this thing working. With them I can't hone in on the correct number just have to hope. Sounds like 1 out of 20 luck.

Apart from that, you might have difficulty using manometric metering in a smallish cannon at low mixes. I don't believe I've tried it below 4x or 5x on my 500ml hybrid.


We're talking this thing not this thing right?
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Unread postAuthor: Zeus » Fri Jan 25, 2013 5:30 am

Look in an automotive store, I've got a great 0-15psi gauge from one, pretty cheap too. It's used for checking the pressure in the manifold.
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/sarcasm, /hyperbole
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Unread postAuthor: CS » Fri Jan 25, 2013 5:38 am

While I'm only doing 2x mixes now, I do later plan to go higher. 0-15 gauges would mean I only could do a 2x mix. I want to see how much pressure this PVC design can handle. To give myself a safety factor.
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Unread postAuthor: MrCrowley » Fri Jan 25, 2013 5:39 am

Ah I getcha, was looking at this topic on my phone and didn't see you were talking about that kind of manometer.
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Unread postAuthor: CS » Fri Jan 25, 2013 5:54 am

Poland got me thinking about purging. How do I purge a U tube manometer or is it necessary? Atomspheric pressure is constant, but that doesn't mean that it is purely air in the manometer when it goes back to zero right?

:?
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Unread postAuthor: mark.f » Fri Jan 25, 2013 7:28 am

At 14.8" column difference I believe your mix is a little lean, although there's not a whole lot of difference between a couple of inches of water.

Are you reading manometric metering as 'Use 0.6174 PSI per mix number' or something else?

Note that 0.6174 PSI has no 'gauge' or 'actual' modifier, it is a change in pressure.

I believe SB15's thread mentions a different number that people use that works.

Because if you were to hook that U-tube manometer up to your cannon, fill with propane until the difference read was 17.1" (assuming 1 PSIG = 27.707 inH<sub>2</sub>O at 60*F), you would have an ignitable 1x mix in your chamber.

If you were to fill until there was a column difference of 34.2", top off to 15.9 PSIG (441.5" column difference :lol: ), you would have an ignitable 2x mixture, and so forth.

My web site is currently down, but I had a write up on where 0.6174 PSI/mix came from. I reuploaded real quick to show you. :P

http://174.129.213.10/hyfuel.html
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Unread postAuthor: wyz2285 » Fri Jan 25, 2013 6:49 pm

Just a quick question I wanted to ask a long long time ago but too embarrassed to do. So in manomatric fueling, there is a certain fuel pressure per mix for each gas, independent from launcher size right? So what's the PSI per mix for butane?
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Unread postAuthor: MrCrowley » Fri Jan 25, 2013 6:56 pm

wyz2285 wrote:Just a quick question I wanted to ask a long long time ago but too embarrassed to do. So in manomatric fueling, there is a certain fuel pressure per mix for each gas, independent from launcher size right? So what's the PSI per mix for butane?
Haha you could've always PM'd one of us :D

To answer your first question: yes. And I think butane is 3.2%. Here's some relevant info provided by Ragnarok:
http://www.spudfiles.com/forums/true-mi ... 16788.html


When I inter-change my meter between my two hybrids (you can do that with manometric setups ;)), I use the same mix numbers for both launchers (10x mix of propane is 6.44 PSI).
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