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| Jeeperforlife |
 Posted: 03/11/2008 20:00 PM Post subject: Plans, what do you think? EDIT added pictures |
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Private First Class
Joined: 15 Jan 2008
Posts: 39
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I have layed low for a few weeks wile I have been working and planning my gun. I will build my first hybrid this weekend and I am wondering what you think of the specs.
6" OD 1/8th" wall steel pipe 30" long, welded 1/4" end caps. 2" union.
For now I plan on using it more for testing for the purpose of building others and making loud bangs. Though I am sure it will get a short barrel at some point.
The steel is some I had left over from a old project. and I have aquired most of the pieces. I will be hard mounting it to a old lawn mower trailer on a turret. It will have a built in compressor and mapp gas tank.
The ignition will be a 15,000 volt transformer for neon lights that will make a 1" ark. I will be putting a simple automotive spark plug in it for now.
A couple of questions I have used burnt lakes gas tool to get the legnth of the meter pipe but I assume the given pressures are for propane. Do I need to modify it for Mapp? It will have wireless remote ignition, what is the highest load I should go?
Last edited by Jeeperforlife on 03/30/2008 0:19 AM; edited 1 time in total |
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| _Fnord |
| Posted: 03/12/2008 10:27 AM Post subject: |
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reenigne
Joined: 13 Feb 2007
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Unless you plan on a 50 foot barrel, that chamber is overkill. WAAAY overkill.
Something 1/3-1/2 of your barrel volume will give about the same result and be much easier to move/fill.
I wouldn't go for higher mixes when you only have a 1/8 wall thickness. Even then you better test it remotely a bunch before you fire it up close.(high, meaning 6x+. )
A 15kv neon sign transformer can light you up pretty good, if not kill you. Why add another potential risk to the equation when a stungun, piezo, or flash+ignition coil will give the same result? (If you're only using one spark gap) |
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| DYI |
| Posted: 03/12/2008 10:49 AM Post subject: |
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Rear Brigadier
Joined: 07 Jul 2007
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I think that, since this is a hybrid, you should do the meter calculations yourself, just to make sure. Remember to take into account gas that will remain in the meter, and the way that more will remain in the meter with every successive injection because of steadily increasing chamber pressures.
Also, I believe that MAPP should be closer to 5% in air, but I don't know the exact number. It contains methylacetylene, propadiene, and propane, for what it's worth, but I don't know the proportions, and there may be other ingredients that aren't mentioned.
If the chamber tube is seamless 304 SS, Barlow's formula would seem to indicate that its failure pressure is ~1300 psi if yield strength is used, and ~3600 psi if ultimate strength is used. 1300 seems to be more likely, but could someone who knows which one to use please tell me? |
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| Jeeperforlife |
| Posted: 03/12/2008 10:49 AM Post subject: |
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Private First Class
Joined: 15 Jan 2008
Posts: 39
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| _Fnord wrote: | Unless you plan on a 50 foot barrel, that chamber is overkill. WAAAY overkill.
Something 1/3-1/2 of your barrel volume will give about the same result and be much easier to move/fill.
I wouldn't go for higher mixes when you only have a 1/8 wall thickness. Even then you better test it remotely a bunch before you fire it up close.(high, meaning 6x+. )
A 15kv neon sign transformer can light you up pretty good, if not kill you. Why add another potential risk to the equation when a stungun, piezo, or flash+ignition coil will give the same result? (If you're only using one spark gap) |
Like I said before this one is just being made from what I have on hand, more to test different fuels, and I am shure at 5X, no barrel it should rival any M80 in noise. I am not really looking for peak performance, I will be making some smaller ones in the future. (though I did just get a 80 gallon compressor take for free). We carry 10 ft pieces if 2" at work so I will probly pick one up for it.
The neon trasnformer I got a few years ago after a sign change at a old job. I have been shocked by it though not directly always though something else with high resittance. The remote is about 20' range and I never plan on firing it in my line of sight. I will always have something in between it and me.
Edit, Just saw DYI's reply.
Part of the point of this is to test different pressures and mixtures. I think I will start with where Burnt lake says and see if I can get some better answers for Mapp. the chamber is mild steel and and does have a seam. I have it left over from some air tanks I was building for my Jeep.
Thanks for the replys. I still have a lot of learning to do. |
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| Jeeperforlife |
| Posted: 03/21/2008 23:19 PM Post subject: |
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Private First Class
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Got it built and now am working out the bugs. I will finish it up and get pictures this weekend. I fired it a few times at just 2X last monday, quite impressed with the power it seems to have.
Two questions,
I am having trouble with burst disks, I have a 2" union and ground down the side with the ridge that goes out. I have a rubber gasket that keeps it sealed very well. But any Burst disk I use pops out at over 50 PSI, it doesn't burst it just pops out. I am going to try Al. flashing, it is .0092" thick and should be right about what I want, I hope. Any ideas?
A wile back I read about a high preshure compressor-generator that went inline with any compressor that multiplied the pressure of the first compressor. It was self powered and could build up to 2000Psi if I remember right. What was it? I have researched and can't find any thing on it.
Marcus |
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| DYI |
| Posted: 03/22/2008 9:06 AM Post subject: |
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Rear Brigadier
Joined: 07 Jul 2007
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Firstly, how much are you tightening the union? You should be turning the knut as far as it can possibly go with an 18" or larger pipe wrench, while bracing it on something solid with another wrench.
I've seen something similar to what you're talking about on McMaster, called a pressure amplifier. They trade flow for pressure, and range from $400 to about $1500. But considering the chamber material, you really shouldn't be pressurising it before ignition to anything higher than your average compressor can generate. |
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| Jeeperforlife |
| Posted: 03/22/2008 9:25 AM Post subject: |
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Private First Class
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| DYI wrote: | Firstly, how much are you tightening the union? You should be turning the knut as far as it can possibly go with an 18" or larger pipe wrench, while bracing it on something solid with another wrench.
I've seen something similar to what you're talking about on McMaster, called a pressure amplifier. They trade flow for pressure, and range from $400 to about $1500. But considering the chamber material, you really shouldn't be pressurising it before ignition to anything higher than your average compressor can generate. |
I am tightening the union with a 24" pipe wrench as hard as I can.
The only reason I want the pressure amplifier is to try different burst disk pressures and i want to build a high pressure pneumatic this summer. |
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| DYI |
| Posted: 03/22/2008 9:34 AM Post subject: |
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| What disk materials are you using? Are they as large as the sealing face of the union? Do you have a picture of the union? Why did you grind down the sealing face? |
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| Jeeperforlife |
| Posted: 03/22/2008 21:47 PM Post subject: |
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Private First Class
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| DYI wrote: | | What disk materials are you using? Are they as large as the sealing face of the union? Do you have a picture of the union? Why did you grind down the sealing face? |
The burst disks have been aluminum foil and two liter plastic. I ground off the inside sealing surface after reading that when it was ground down and a rubber gasket was added it sealed better. I have been having problems with the burst disk on my pneumatic not sealing so I tried this. I will get pictures of it tomorrow.
Edit I could not get down to the shop to get pictures today. I will get them this weekend. I also hope to get the barrel done and everything painted. |
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| Jeeperforlife |
| Posted: 03/30/2008 0:27 AM Post subject: |
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Private First Class
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I got a few pictures tonight. They should be pretty self explanatory. Post up if you have any questions. I need to get the barrel still, it will be 10 foot 2" steel conduit.
This is my first hybrid so don't expect much. A few things I need to do is support the metering chamber, redo the igniter, I'm adding spark plugs top and bottom.
My second one is turning out better.
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| sniperjosh |
| Posted: 03/30/2008 6:09 AM Post subject: |
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Specialist
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| what a beast, gigantic chamber. |
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| DYI |
| Posted: 03/30/2008 9:18 AM Post subject: |
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| Welding looks a tad messy, but overall pretty good. How thick are the end plates? I'd suggest no less than 1/2" for 6" pipe, as 4" pipe should have caps at least 1/4" thick for 10x, and 6" has twice the cross sectional area. Igniting from the front may not be the best idea though... |
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| SpudFarm |
| Posted: 03/30/2008 13:59 PM Post subject: |
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Hybrid Guy
Joined: 04 Nov 2006
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why not ignite in the front DYI?
the shot is not fired until the disk goes...
500 posts  |
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| DYI |
| Posted: 03/30/2008 15:14 PM Post subject: |
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Rear Brigadier
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I just reread his post, and it said that he was adding more ignition points. So there's no problems, other than the rather thin pipe.
This forum seems to be getting a lot of monster hybrid projects, doesn't it spudfarm?  |
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| Jeeperforlife |
| Posted: 03/30/2008 23:25 PM Post subject: |
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Private First Class
Joined: 15 Jan 2008
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| DYI wrote: | | This forum seems to be getting a lot of monster hybrid projects, doesn't it spudfarm? |
Inside joke?
Thanks for the replys. the welds and spatter have not seen the grinder yet. I will paint the chamber. I am going to switch over to duel ignition once I get it on the tripod. the end caps are just 1/4 inch but I don't plan on taking it over 6X. I have rethought the barrel and am going to try to find a stick of 2.75" exhaust pipe to shoot concrete filled coke cans. |
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