Oxy/Propane mix in Sch 80 PVC; Is it safe?

[WizardNoodle]

I am planning on making a Sch 80 PVC Combustion Cannon with a 3 inch chamber at the start of the Summer, and am not satisfied with the currently projected power.
If I inject 20% of the Chamber's Volume in Oxygen, and then 8.6% Propane, will that be equal to a 2x mix in a Hybrid?
I understand that at 4x mix you have a risk of DDT and PVC is less than suitable for the mix, but is 2x safe enough for a PVC Combustion, or will I end up with a one-way trip to the ER?

Thank you for your time

[mark.f]

At one point in time, people would say yes. However, opinions change over here over time, and nobody uses PVC for hybrids anymore; and for good reason.

Do yourself a favor and go with a better construction material.

[WizardNoodle]

"Do yourself a favor and go with a better construction material."

I would like to, but my planned budget doesn't exceed 200$ and I simply don't have the tools and skills to work with metal, and definitely not enough cash to hire a machinist.
I don't want to make a Hybrid just yet, but I don't want a half ass gun either, hence my question about the safety of injecting 20% oxygen + 8.6% propane into a combustion.

[jackssmirkingrevenge]

I would personally avoid playing with oxygen altogether. For a pressurized 2X hybrid all you would need to do is add a schrader valve somewhere and use a barrel coupling that will take a burst disk. You don't need a complex fueling system either, a large syringe will do.

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Simply multiply the calculated fuel by your mix number.

[WizardNoodle]

I would personally avoid playing with oxygen altogether. For a pressurized 2X hybrid all you would need to do is add a schrader valve somewhere and use a barrel coupling that will take a burst disk.

So if I am switching the design to a Hybrid, is it safe if it is a handheld Sch 80 PVC Hybrid without remote ignition, as long as it runs under 3x mix, or whatever is deemed safe for PVC? (Definitely not exceeding 4x)

[jackssmirkingrevenge]

Here's an HGDT simulation of a 3 inch chamber hybrid at 3X where the burst disc is too strong and doesn't burst, a worst case scenario giving you maximum chamber pressure:

As you can see, it maxes out at 330 psi.

Schedule 80 PVC has a burst pressure of 1200 psi and working pressure of 225 psi, safe to say that even in this scenario a correctly manufactured pipe would not burst. In practice of course if you run only at 2X and use an appropriate burst disk, chances of a chamber rupture are virtually zero.

Nothing is 100% safe of course, but in this case competent assembly of fittings is much more critical, as it is more probable that a poorly attached fitting will fail than the material itself.

[WizardNoodle]

Here's an HGDT simulation of a 3 inch chamber hybrid at 3X where the burst disc is too strong and doesn't burst, a worst case scenario giving you maximum chamber pressure:

hgdt3inch.jpg

As you can see, it maxes out at 330 psi.

Schedule 80 PVC has a burst pressure of 1200 psi and working pressure of 225 psi, safe to say that even in this scenario a correctly manufactured pipe would not burst. In practice of course if you run only at 2X and use an appropriate burst disk, chances of a chamber rupture are virtually zero.

Nothing is 100% safe of course, but in this case competent assembly of fittings is much more critical, as it is more probable that a poorly attached fitting will fail than the material itself.

Thank you so much for that data, unfortunately, I cannot use HGDT as I have a new computer, which is a Chromebook
You mention that it is more likely for a poorly attached fitting to fail than the pipe itself, would this fail because of the manufacturer/material or someone who poorly solvent welds the pieces together?
Also the barrel diameters I would use are
2" sch 40(I don't feel like having a barrel 16 feet long, the smaller diameter of the barrel should counter the lower wall thickness... right?)
sdr 21 sleeved in (2 inch, I think?)sch 80 PVC, and
2.5" Sch 40

Thank you so much for replying to and helping me.

[jackssmirkingrevenge]

You mention that it is more likely for a poorly attached fitting to fail than the pipe itself, would this fail because of the manufacturer/material or someone who poorly solvent welds the pieces together?

The latter, you have to be absolutely sure that you weld it according to the manufacturer's recommendations, otherwise you might get an endcap as a projectile.

Thank you so much for replying to and helping me.

No worries, I went head and ran more typical numbers and as you can see with a 4 inch long potato slug you'll have the same energy as a .44 Magnum Note also that peak pressure does not exceed 250 psi, well within the limits of the materials if correctly put together.

[WizardNoodle]

No worries, I went head and ran more typical numbers and as you can see with a 4 inch long potato slug you'll have the same energy as a .44 Magnum Note also that peak pressure does not exceed 250 psi, well within the limits of the materials if correctly put together.

hgdt2inchhybrid.jpg

That is so awesome, I would never have dreamed of that much power!! I know it seems inferior to all you welding machinists, but it is more than I would have dreamed of!!
Now all I have to do is build it correctly.

OH and I forgot to mention,
#1 I might as well give the specifics of the chamber and length if this is going to be completely accurate, chamber is 231.92" cubic inches, or 3" Diameter(Could this be too small of a diameter relative to a barrel of 2" or 2.5"? Should I change the Diameter to 4", keeping the cubic inches constant?) with 3' in Length if it's straight(This will be an over/under cannon),
barrel(s) will be 288.524" cubic inches, or 2" Diameter at 87.5 inches in Length and 2.5" Diameter at 58.78125 inches in Length.

#2 I am also considering using MAPP instead of propane. It sounds like it would be pushing it, but is it still safe to use in PVC?

Again thanks for your time, that comment about it's energy relative to a .44 Magnum has completely made my day!
(I was riding my horse and all I could think were the words "...more energy than a .44 Magnum...")

[jackssmirkingrevenge]

That is so awesome, I would never have dreamed of that much power!! I know it seems inferior to all you welding machinists, but it is more than I would have dreamed of!!

Hot gas and the instant "valve" certainly gives hybrids the edge when it comes to raw power.

Don't forget that with great power comes great responsibility

(Could this be too small of a diameter relative to a barrel of 2" or 2.5"? Should I change the Diameter to 4", keeping the cubic inches constant?)

No, you're fine with the 3" - smaller diameter is stronger and safer.

I am also considering using MAPP instead of propane. It sounds like it would be pushing it, but is it still safe to use in PVC

The percentage difference is too low to be significant compared to the safety factors involved.

Again thanks for your time, that comment about it's energy relative to a .44 Magnum has completely made my day!
(I was riding my horse and all I could think were the words "...more energy than a .44 Magnum...")

Well you'd better sit down for this then, with your numbers HGDT suggests that with a lightweight projectile in the 2 inch barrel you could go supersonic, while a heavy projectile in the 2.5 inch barrel you'll have muzzle energies approaching a 12 gauge shotgun slug:

This means a hefty recoil too, you're probably better off with an inline as opposed to an over-under design that will avoid putting torque on the elbow.

[WizardNoodle]

That is so awesome, I would never have dreamed of that much power!! I know it seems inferior to all you welding machinists, but it is more than I would have dreamed of!!

Hot gas and the instant "valve" certainly gives hybrids the edge when it comes to raw power.

Don't forget that with great power comes great responsibility

(Could this be too small of a diameter relative to a barrel of 2" or 2.5"? Should I change the Diameter to 4", keeping the cubic inches constant?)

No, you're fine with the 3" - smaller diameter is stronger and safer.

I am also considering using MAPP instead of propane. It sounds like it would be pushing it, but is it still safe to use in PVC

The percentage difference is too low to be significant compared to the safety factors involved.

Again thanks for your time, that comment about it's energy relative to a .44 Magnum has completely made my day!
(I was riding my horse and all I could think were the words "...more energy than a .44 Magnum...")

Well you'd better sit down for this then, with your numbers HGDT suggests that with a lightweight projectile in the 2 inch barrel you could go supersonic, while a heavy projectile in the 2.5 inch barrel you'll have muzzle energies approaching a 12 gauge shotgun slug:

hgdt3inchhybrid.jpg

This means a hefty recoil too, you're probably better off with an inline as opposed to an over-under design that will avoid putting torque on the elbow.

I just stopped screaming. I honestly have no words. Mom is rolling her eyes, "Why don't you just get an actual 12 Gauge? Why do you have to make it?" BECAUSE I CAN.
Thank you so much for running that simulation for me, I have been planning and designing this gun, but to hear what the projected values are... :bounce:

Oh, and what is an inline design? I suppose it would be heavy recoil... maybe I could glue some foamboard to where it will be pressed against my shoulder, should soften the blow.

[jackssmirkingrevenge]

When you put the chamber under the barrel it's a more compact design but the elbow or tee connecting them becomes a weak point, with PVC it's better to have the chamber in line with the barrel.

I am so excited ohmygosh only a couple more weeks

Enthusiasm is fine but don't let it stop you from doing things slowly, deliberately and most of all, safely.

[WizardNoodle]

When you put the chamber under the barrel it's a more compact design but the elbow or tee connecting them becomes a weak point, with PVC it's better to have the chamber in line with the barrel.

I am so excited ohmygosh only a couple more weeks

Enthusiasm is fine but don't let it stop you from doing things slowly, deliberately and most of all, safely.

I could coat the elbows in primer, make a rough mold, and fill it with cement :bom:

And of course, I will approach this project with much premeditated thought and carefulness, like I read somewhere, if a combustion cannon fails your out a few bucks but if a hybrid fails you're dead.

[WizardNoodle]

When you put the chamber under the barrel it's a more compact design but the elbow or tee connecting them becomes a weak point, with PVC it's better to have the chamber in line with the barrel.

Hang on a second- I always thought that working with metal meant welding/machining, but could I build the cannon out of threaded metal pipe and adapters, with the threads wrapped in Teflon tape?

I saw Mr Crowley's Piston Golfball Hybrid, and it seems like that is what he did!
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Do you think I could abandon PVC altogether and go all metal? It would be more costly, but not half as much as it would cost to pay someone to weld it together, and I would be able to go significantly higher in power, while staying 100% safe.

[wdr0]

Yes, you can use threaded metal pipe, there are a number of other joining methods for metal piping not involving welding as well although likely out of your price range. As another note, it might be beneficial to make the effort and find a welder. I've built a large cannon out of sch 80 pvc and another out of welded steel. The steel weld fittings were cheaper than pvc by far in the larger sizes.