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First Hybrid

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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Unread postAuthor: rp181 » Mon Apr 07, 2008 6:46 pm

I started making my first hybrid with just things i find, (i live in a neighbor hood with alot of construction going on). Rightnow, i have a pressure guage connected to a tee, going to a schrader valve and to a ball valve. The valve goes to 2 90 degrees for a U-turn to reduce length.

Now my question is, do pressure guages get ruined from peak pressures? i put the ball valve as a precaution, but is it really nesscary?

All i need is a chamber. How much pressure can a regular nipple handle?
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Unread postAuthor: pat123 » Mon Apr 07, 2008 6:53 pm

You need a valve before the gauge. do you make a meter yet. can you post some pics. what type of material are you using? steel, copper hopefully a metal.
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Unread postAuthor: STHORNE » Mon Apr 07, 2008 6:53 pm

yes, especially with combustions/hybrids. if you didn't have the ball valve protecting the pressure gauge, it would be ruined from the spike in pressure when the gas is ignited.

a nipple can pretty much handle whatever pressure you throw at it (since its being used for a hybrid). I think the maximum pressure they can take (and correct me if I'm wrong) is 460 psi? not sure, but either way, you will be fine.
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Unread postAuthor: pat123 » Mon Apr 07, 2008 6:57 pm

I think the maximum pressure they can take (and correct me if I'm wrong) is 460 psi?

he never said what kind of material he was using. sch40 steel can easily take 460 but sch 40 pvc might not take 200. either way the nipple is the strongest part of the gun, worry about the fittings.
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Unread postAuthor: bigbob12345 » Mon Apr 07, 2008 6:59 pm

Depends on the size but a regular hardware store steel nipple wont burst until ~2000psi but a moderately safe limit would be a 6x mix which is ~650psi.
But most people dont tend to take them above 5x.
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Unread postAuthor: STHORNE » Mon Apr 07, 2008 7:00 pm

we are talking about the nipple and what pressures it can take, not the chamber itself.
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Unread postAuthor: bigbob12345 » Mon Apr 07, 2008 7:03 pm

Well the chamber is a nipple so....
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Unread postAuthor: STHORNE » Mon Apr 07, 2008 7:06 pm

pretty sure they don't make pvc nipples though, so the argument is pointless whether it can take the pressure or not.
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Unread postAuthor: bigbob12345 » Mon Apr 07, 2008 7:08 pm

Oh he is talking about pvc
And you can get pvc nipples just only in sch80
Well if you are using pvc then just scrap your plans and build it out of metal if you want to go above a 1.5x mix safely
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Unread postAuthor: rp181 » Mon Apr 07, 2008 7:09 pm

All metal, i was talking about the hardware store steel nipple. I wasn't planing on taking it past 3x, but might occasianally do 5x. For the metering do i need to do the standard cumbustion way? I was planing on filling the chamber with air to a certain PSI, then adding propane to meet final PSI req. The guage goes to 35 PSI, at 1/2 psi intervals, so i think itle be pretty acurate. If its the standard way, then the volume is a bit small =/

Image

Bit dirty, ile sand it later.
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Unread postAuthor: pat123 » Mon Apr 07, 2008 7:12 pm

you want the meter seperate from the area the air comes in. I broke the valve on my propane tank like that.
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Last edited by pat123 on Mon Apr 07, 2008 7:57 pm, edited 1 time in total.
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Unread postAuthor: bigbob12345 » Mon Apr 07, 2008 7:12 pm

Hmm very small chamber
and you are supposed to fill it with propane before you put the air in otherwise it will bring the pressure into the meter so you would have to unsrew something to realease the pressure before the next shot

just use the standred combustion metering but just make it very small

sorry if this post is hard to understand as i worded it horribley
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Unread postAuthor: rp181 » Mon Apr 07, 2008 8:07 pm

The chamber isnt even there :)

The 90 degree will connect to the chamber.

To *meter*, im first pumping to the needed pressure, take the pump head of, and connect to the propane and fill compared to whatever is left.

If i wanted 100psi, i would put 95+~5psi of air, take of pump, and because some will leak out, let some out so it actually is 96 psi, and fill rest with propane.

Then ile close the ball valve to protect the guage, and fire.
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Unread postAuthor: DYI » Mon Apr 07, 2008 8:17 pm

To *meter*, im first pumping to the needed pressure, take the pump head of, and connect to the propane and fill compared to whatever is left.

If i wanted 100psi, i would put 95+~5psi of air, take of pump, and because some will leak out, let some out so it actually is 96 psi, and fill rest with propane.

Then ile close the ball valve to protect the guage, and fire


Alright, who wants to place bets on how many years it is before he gets a shot? :roll:
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Unread postAuthor: rp181 » Mon Apr 07, 2008 8:58 pm

:wink: naa, its quite fast. Do you think ile be better off using the current setup as a standard combustion metering? With the small volume, ide think it would take a while, but then again im using a small chamber. Ile try both ways.
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