Piston Valves Explained Visually
Plz look throught the forum. Also check the wiki. Ask reasonable questions plz. This is not the place to ask. Do research first then ask what you cant find answers to after doing extensive research.
4SPC, My 4" piston 3" porting cannon
Memo:
Fix up copper cannon
Fix up 4SPC
Start Stirrup pump
Start Toolies piston bazooka
Memo:
Fix up copper cannon
Fix up 4SPC
Start Stirrup pump
Start Toolies piston bazooka
Use your ingenunity. You can make pistons out of lots of different things. Mine was made out of a length of bolt with washers on it (but that's only useful at low calibres), some people use PVC endcaps, some people lathe them from PVC rod... making the piston just requires a little lateral thinking.anthony5640 wrote:how do i make a piston?
Does that thing kinda look like a big cat to you?
- schmanman
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I once made a piston out of:
part of the front of one of these badmittion thingies
a piece of surgical tubing
a piece of 1/4 inch air hose
a piece of bike innertube
a piece of a pencil
a piece of a marker cap
a small piece of duct tape
....And some gorilla glue
It actually worked great for about 70 shots, then the barrel cut through the badmittion thingy, and it died.
then I used it as ammo....
part of the front of one of these badmittion thingies
a piece of surgical tubing
a piece of 1/4 inch air hose
a piece of bike innertube
a piece of a pencil
a piece of a marker cap
a small piece of duct tape
....And some gorilla glue
It actually worked great for about 70 shots, then the barrel cut through the badmittion thingy, and it died.
then I used it as ammo....
Persistence is a measure of faith in yourself
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One thing I missed trying to build my own piston was 'frontal pressure' applied to the front of the piston when pressurized.
In Phase Three where it's stated, "Once the force pressing on the back of the piston falls below the force acting on the front of the piston, it begins to slide back. Suddenly there is more surface area exposed on the front of the piston, and the jump in force slams the piston back leaving an opening for air to flow into the barrel to accelerate the projectile. " I didn't quite pick up on this part of building a piston until after I had built one. Of course common sense says the piston front face has to be larger than the port to which it seals. From what I've discovered this frontal pressure is the 'pressure' that's on the residual area of the seal around the port.
Now, my piston still opened even though I built it with no area for frontal pressure. It wasn't performing at its best, even though it would fire a spud 150 yds, it was trying to suck the seal through the barrel nearly tearing it on every fire. I ended up painstakingly adding a sleeve that protruded into the chamber to give it this frontal pressure needed.
Forgive me Clide, I snatched part of your FLASH.
In Phase Three where it's stated, "Once the force pressing on the back of the piston falls below the force acting on the front of the piston, it begins to slide back. Suddenly there is more surface area exposed on the front of the piston, and the jump in force slams the piston back leaving an opening for air to flow into the barrel to accelerate the projectile. " I didn't quite pick up on this part of building a piston until after I had built one. Of course common sense says the piston front face has to be larger than the port to which it seals. From what I've discovered this frontal pressure is the 'pressure' that's on the residual area of the seal around the port.
Now, my piston still opened even though I built it with no area for frontal pressure. It wasn't performing at its best, even though it would fire a spud 150 yds, it was trying to suck the seal through the barrel nearly tearing it on every fire. I ended up painstakingly adding a sleeve that protruded into the chamber to give it this frontal pressure needed.
Forgive me Clide, I snatched part of your FLASH.
I know on a coaxial and barrel sealing piston, the piston has to be considerably larger than the exhaust in order for the forces to make it work, however, I wouldn't think that would apply to a chamber sealing piston valve. Is my assumptions correct?
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Yes, but working and performing well are different things. If you make a chamber sealing valve with the seat the same size as the piston then you'll have relatively crappy opening times and piston bouncing issues unless you have a monster pilot valve...I wouldn't suggest it.hubb017 wrote:I know on a coaxial and barrel sealing piston, the piston has to be considerably larger than the exhaust in order for the forces to make it work, however, I wouldn't think that would apply to a chamber sealing piston valve. Is my assumptions correct?
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Thanks. I was considering a chamber sealing valve on my next project but I got it it worked out to go with a barrel sealer (which was what I preferred anyway).
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great info. i understand them now but i don't think i can make one just yet. ill experiment for a while until i really know what i am doing
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Although reducing the pilot volume will be beneficial, as Pete said: your pilot valve is a more important factor.Pete Zaria wrote:Yes, too much pilot volume is a common problem. A larger pilot valve does help, though it's best to try to reduce this volume somehow, either by re-designing the valve or filling the volume with something (foam anyone?).octane89 wrote:Can someone answer this for me-
Is it possibly to have too much pilot volume? I have a 3" Tee, and the pilot volume is about the size of a 3" cap.
A picture would be helpful...
Peace,
Pete Zaria.
By using a QEV (quick exhaust valve) as your pilot valve, you'll be able to dump that pilot chamber's air faster than you can say 'cat in a hat'.
In my opinion, with a QEV as your pilot valve, you won't have to reduce the pilot volume in the first place...
ps You can find QEV's at pneumatic supplies shops (the guys that sell compressors and stuff) otherwise google it!
Cheers
Rob
EDIT: I've found agreat QEV manufacturer - although they're based in the EU, they have international distribution and are by far the cheapest I've been able to find.
.http://www.eurofit.it/prodotto_dettagli ... rod_id=117