Need help with piston valve design

[spudlicker2x]

I am in process of building a hybrid, but am lost when it comes to building a good valve idea. My other hybrid used burst discs, but the problem with that is they need to be changed after ever shot. Any ideas would be helpful

Edited by jrrdw, don't use all caps in titles.
Misleading topic title edited by MrCrowley

[Mr.Tallahassee]

First help, I think the title should be different to avoid confusion. Second, if you are VERY good with your hands and extremely good with math then a piston hybrid is not out of the realm of possibility. Mr.Crowley is the person to consult about piston hybrids seeing as he has a fully functional hybrid.

[wyz2285]

valve less?

[spudlicker2x]

i want to make it where i no longer have to use burst discs. it makes the reloading process that much longer

i guess a piston valve set up is the way. it is the part of knowing how to make it is my issue

Edited by jrrdw, double posting use the edit button if no one posted under your last post.

[jrrdw]

First help, I think the title should be different to avoid confusion. Second, if you are VERY good with your hands and extremely good with math then a piston hybrid is not out of the realm of possibility. Mr.Crowley is the person to consult about piston hybrids seeing as he has a fully functional hybrid.

After a design is posted you may ask for help in the Hybrid section. Absolutely no spoon feeding in this section!

[SpudBlaster15]

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[MrCrowley]

i want to make it where i no longer have to use burst discs. it makes the reloading process that much longer

i guess a piston valve set up is the way. it is the part of knowing how to make it is my issue

If you've never made a barrel-sealing piston valve for a pneumatic before, do that first.

If you have, it's not as difficult as it sounds.

Make a piston that has at least one o-ring (two is better) to seal off the pilot from the chamber 100% (important). The piston has to be able to withstand huge amounts of force so it can't really be built from plastics or wood. Mine is made from bolts, washers and nuts. You can find pictures of my piston in my hybrid thread in the showcase section.

Now that your piston is made, I suggest you take the same route with the pilot valve that I did (thanks goes to SB15 for the design), it shouldn't be difficult for you to figure out how it works and how to make it if you've built pistons before and hybrids before. The key here is high flow, you'll have lots of problems if you don't have enough flow through the pilot such as piston bounce (which will absolutely destroy the piston face).

Now that's about it. The hardest thing is making the piston last for a reasonable amount of time and getting everything to seal, the actual design and operation is relatively simple.

There's enough information in the hybrid discussion section and showcase section to get you started. I just realised I built mine without even creating a thread to discuss how to do it. You'll only really need help on making the piston: things like getting the o-rings to seal, epoxying the washers and nuts, finding a decent sealing face and figuring out how to make a seat (what the piston seals against) in a malleable iron tee fitting are small problems that can frustrate the heck out of anyone, thankfully I can help you fix all those problems.

[spudlicker2x]

thank you for the replies. I will post some pics, and drawings of my design. I understand the concept of the piston valve design. I guess that i am not inclined enough to make my own design for it, and or incorporate it in my design.

[Moonbogg]

I wonder if using thick, hard rubber as well as a fairly wide sealing face might help eliminate piston damage from any piston bounce that may occur. Thats kind of what I am banking on for my design at the moment.

[MrCrowley]

I found out that it is much easier preventing piston bounce than preventing the sealing face getting destroyed. In any case, I've found that the rubber rollers used on boat trailers to guide the boat's hull work extremely well. Previously I had used a hard rubber bung (also for a boat) but that was quickly destroyed though at the same time I installed this harder, new rubber from boat trailers, I had also seemingly fixed the piston bounce issue by increasing pilot flow.

If your seat was about 5mm thick, flat (not sharp like the end of a galv. pipe nipple) and the piston face was made of a similar hard rubber with adequate support (2-3mm thick steel washer, my zinc one bent), you could probably get away with piston bounce for a couple dozen shots. Mind you, piston bounce probably has a noticeable effect on performance so it might not be a good idea to just put up with it.

A roller like this would work well for a sealing face:


They're cheap and come in sizes ranging from about 1.25" to 4". I'm sure you guys in America can find hard rubber sheet online or elsewhere but for those who can't, the above works well.

Anyway, just throwing my $0.02 out there.

[Moonbogg]

Yeah, venting is better i'm sure. its just more challenging

[wyz2285]

hum I never made a piston hybrid, but they looks good to me
I´m good at pneumatic pistons, but in a hybrid, do I need a pilot or something like that? a safety valve?

[MrCrowley]

hum I never made a piston hybrid, but they looks good to me
I´m good at pneumatic pistons, but in a hybrid, do I need a pilot or something like that? a safety valve?

You don't need one but I would recommend one. I think ramses never had a pilot for his piston, can't remember whethere Fnord's piston hybrid did or not. In the case of ramses' cannon, I believe the pilot was filled with air to act as an air spring.

I think it's worth putting in the extra effort for a pilot, SB15's design is quite simple and easy to build compared to the piston itself.

[wyz2285]

I think I have saw his pilot, but didn't understand how does it work. The valve with a pilot is faster than without the pilot right?

[MrCrowley]

I would assume so, yes.

The pilot design is very simple. The piston is forced back, the pilot spool is attached to the piston so is also forced back, this unseats itself and exhausts the pilot air.