SpudFiles

G'day everyone,
I am building my first hybrid, its made out of 90 mm ID x 8 mm wall steel pipe.
I want to use a piston valve, I've already had one attempt, but I figured out what went wrong, I made the piston smaller than the sealing face and it can't overcome the force holding it shut.

Here's some photos of construction, the plate on the back of the tee will have to go to accommodate my modifications for the new piston setup ( in the middle of making it). I was wondering what fuel metering to use ? Manometric, or Volumetric
I will upload some more photos soon of the rest of it

Some more information as to the mixtures you're planning on using would be very helpful. Based on your previous creations (and username), I assume it's hydrogen and oxygen.

Any piston valve you build would need to have some pretty beefy construction. You could take advantage of hydrogen's wide flammability range to add more fuel to absorb heat during combustion, lowering peak pressure but perhaps lengthening the lifetime of your valve.

Of course this is all speculation... any specifics on the mixture you should be using?

Also, google "Utron hydrogen type:pdf" to get your hands on what you can by former DoD contractor Utron, which details their work on fuel/oxidizer composition.

Hi,
Thanks for replying so quickly,
The fuel I hope to use for this gun is Propane.
My other guns have been just combustion, my electrolyser cell doesn't produce high pressures, and I don't!! Want to compress hydrogen and oxygen mix....BOOM

The piston material will be steel hopefully if I can find the right size material in the scrap heap.
As soon as I find something I will post some pics so you can see what you reckon.

Regards burning water

Sounds good.
For the piston, aluminum should be perfectly adequate for propane mixes. The lighter weight would reduce stress at the back of the valve less as well.

Hi Mark
I don't have any access to some aluminum bar stock so, I was wondering if steel pipe with two end caps would be ok ?

It would work but anything you could do to reduce weight while maintaining strength is a good call. Considering pipe and fittings are lighter than solid steel stock you're heading in the right direction.

This is going to be one serious gun if this thing works.
The piston would be over 65 mm across.
BTW the piston would be welded not fittings. And I have a lathe

How did you remove the seem?

Hi mate,
I used a file and sand paper to remove the seam, then I honed it with a drill engine reamer

I thought you would have used the lathe then custom fitted the piston. I guess it was already welded together at that point?

Yeah I would have used the lathe if I had a long enough boring bar.
I have got about halfway doing the piston, it seems to be sealing well :bounce:

The piston is done, I just have to work on the front and back sealing faces now.
Heres a photo of the piston
At very low pressure (10-20 psi) you can't hold the piston in, it seems like it will work well.
The piston is also very light, so it should actuate fast.

Do you think the threaded rod will handle the stress ?

It was either MrCrowley or Spudblaster15 had a lot of trouble with threaded rod. Search their hybirds follow the fix so you don't tear up what you've build so far.