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Piston - Quick question

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Piston - Quick question

Unread postAuthor: SpoonZ » Tue Jun 26, 2007 6:54 am

If I understand Pistons fully. When making a Barrel sealing T valve you need your equalization holes to only fill one way? So that the chamber cannot leak back into the pilot space? Is this correct?

If so. How do I do this?

Ive searched. But I'm a search nub. But I'm sure you need to seal the equalization hole from blowing back into the pilot space.
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Unread postAuthor: jackssmirkingrevenge » Tue Jun 26, 2007 7:02 am

you don't *have* to seal it as long as your pilot valve has a greater flow than your equalisation hole
. Unless you're using o-rings or a 100% airtight fit rubber piston, you don't even need an equalisation hole - in the former case however you can either have a check valve between the pilot chamber and the main chamber (letting air into the main chamber but not back into the pilot) or have separate filling valves for pilot and main.

However if you're piloting with a modded sprinkler or ball valve and you have a 1.499" piston in a 1.500" chamber you don't have to worry about equalisation holes at all.
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Unread postAuthor: SpoonZ » Tue Jun 26, 2007 7:10 am

Well mine will be sealed fully. With O-rings. So I most probably Pilot with a sprinkler valve.
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Unread postAuthor: spudthug » Tue Jun 26, 2007 8:37 am

why? orings dont increase performance...they mgiht even slow the piston down..you only need orings in a chamber sealing valve...
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4" piston valved cannon-half done..( i spilt my cement...)

Hybrid- 75% done. need to build propane holder and drill/tap sparkplug hole..
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Unread postAuthor: mark.f » Tue Jun 26, 2007 8:40 am

Well, if such is the case, then you really don't need a sprinkler valve to pilot the piston. If there's a 100% seal between the piston and the carriage, all you need to do is just drill a 1/32" equalization hole or two and pilot with a ball valve.
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Unread postAuthor: MrCrowley » Tue Jun 26, 2007 2:47 pm

spudthug wrote:why? orings dont increase performance...they mgiht even slow the piston down..you only need orings in a chamber sealing valve...


Spudthug know what you're talking about first, by having o-rings or a 100% sealed piston you can pilot/vent the piston with a smaller diameter ball valve/blow gun also you save more air and pressure from getting wasted out the pilot valve. Also if it is o-ring sealed you can seal the piston and actuate the piston at much lower pressures. There are some very good advantages.

On a current project im working on it took a 1/2" ball valve to vent my 2" piston, thats crazy. That is how bad the seal between piston and tee housing was. It also wouldn't seal at under 35psi and actuate under 50psi. Also when I vented it I lost half my pressure because of the huge valve. Now that I have added o-rings I can seal the piston at about 20psi, actuate it at 30psi and only use a 3/8" ball valve to vent it.
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Unread postAuthor: Modderxtrordanare » Tue Jun 26, 2007 4:25 pm

spudthug wrote:why? orings dont increase performance...they mgiht even slow the piston down..you only need orings in a chamber sealing valve...


As MrCrowley mentioned, O-Rings do help with preformance, reducing wasted air and instead using it towards moving the projectile.

Also, they won't slow the piston down if you lubricate the o-rings properly. :wink:
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-How-To: Modding a Sprinkler Valve
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