SpudFiles

Hi everyone.
As I started building hybrids, I loved it.
But changing burst disc it not fun at all so I took a little research about piston hybrids. But I really don´t understand how do they vent the pilot air when it fires so I made 2 diagrams, the first one shows 2 type of piston hybrid valve that I thought would work, and the second diagram shows a fast venting chamber that I think will work both for hybrids and combustion.
Any thoughts? I think I won´t have problem machine the pistons out of nylon, but is nylon strong enough?

You could just use a reasonably strong spring inside the pilot chamber behind the piston, and add a small hole in the back of the pilot so the air can vent. Most people do this, as they tend to fill their cannons directly into the chamber.

Crowley and SB15 built the design of the right, mine is like the one on the left but without the popoff valve.

Both will work, but the one on the right will have less piston bounce. That means it's also critical to use a good bumper in this design. Nylon should be workable.

The quick-vent chamber is a very good idea, but in practice you may have sealing issues with the orings eventually. Hybrids get kinda dirty inside.
Make sure all threaded rods in the design are strong enough to take the forces involved.


Alster:
Been there, done that;

Another option would be a check valve in the pilot region that allowed air to flow into the main chamber.

D_Hall wrote:Another option would be a check valve in the pilot region that allowed air to flow into the main chamber.

If I understand you correctly, that would only work if the pilot pressure was lower than pre-ignition pressure?

@Fnord, LOL. Been there, done that twice

As Fnord said, a good bumper is crucial to the design me and SB15 used. You also need a decent flow out the pilot valve to help stop piston bounce. I imagine that if you get piston bounce, your nylon piston will almost certainly break after a few shots. However, if you get everything right and piston bounce is not an issue nylon should be fine.

You will pay a bit in terms of performance but it should still be decent. I built a piston hybrid because I wanted a large hybrid and cutting out disks for a 2" union is crazy. I don't find burst disks too troublesome for my 3/4" burst disk hybrid; you just need to find what works. I use a modified union (tapered union face has been ground flat for more surface area to hold the burst disks), 4 o-rings all of the same size which stack up inside one half of the union and provide a seal and then 4 soda can disks with a very slight scored mark on them to help them burst cleanly at 10x.

MrCrowley wrote:

D_Hall wrote:Another option would be a check valve in the pilot region that allowed air to flow into the main chamber.

If I understand you correctly, that would only work if the pilot pressure was lower than pre-ignition pressure?

Or equal to. True, the pilot pressure could not be more than the pre-ignition pressure (plus a couple psi, depending upon your check valve selection).

As im in the process of designing my own piston hybrid, would the top left diagram work without the pop off valve? I would assume that all the resulting gas would have left the chamber by the time the piston could react and return back to its position?

Alster370 wrote:As im in the process of designing my own piston hybrid, would the top left diagram work without the pop off valve? I would assume that all the resulting gas would have left the chamber by the time the piston could react and return back to its position?

Yes, but not as well as with a pop off you will diffidently get piston bounce that will demolish your sealing face/piston.

*word that BtB would chose to censor*

Alster370 wrote:As im in the process of designing my own piston hybrid, would the top left diagram work without the pop off valve? I would assume that all the resulting gas would have left the chamber by the time the piston could react and return back to its position?

I wouldn't recommend it personally. I think it was ramses who used the "air spring" concept in his design, not sure how it worked out in terms of piston bounce.

jackssmirkingrevenge wrote:*word that BtB would chose to censor

It seems that BtB is more than happy to substitute his name for that word; now we have a synonym we can use

Change of disk is fast on my hybrid (Thorjack), this is not a constraint because I put the bullet at the same time....

It would suck cutting disks for a 2" union
It's annoying enough to spend 15min cutting 12 disks from a soda can that last only 3 shots at 10x.

MrCrowley wrote:It seems that BtB is more than happy to substitute his name for that word; now we have a synonym we can use

hmmm...

"You utter Brian!"

Actually, it does have a ring to it

effectively is a long time ...
they are discs steel or aluminum?