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Pop off valves

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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Pop off valves

Unread postAuthor: Major Collins » Wed Feb 08, 2012 8:53 pm

With pop off valves do they just pop once and let the extra air out in 1 go or will it pop numerous times letting the pressure ?
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Unread postAuthor: usdiver63 » Thu Feb 09, 2012 12:05 am

numerous times and then they reseat themselves, you can either pull them manually or they go off at a preset pressure.
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Unread postAuthor: cannon monkey » Thu Feb 09, 2012 12:20 am

not 100% sure on this but when my buddy pulled his open it stayed open until he pushed it closed
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Unread postAuthor: mobile chernobyl » Thu Feb 09, 2012 12:27 am

They only self-close when the "pop-off" pressure is no longer present in the tank.

pop-off_true = If pressure in tank > pop-off pressure

Your also likely to experience a bit of hysteresis in a pop-off valve due to the mass flow of air.
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Last edited by mobile chernobyl on Thu Feb 09, 2012 12:28 am, edited 1 time in total.
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Unread postAuthor: usdiver63 » Thu Feb 09, 2012 12:28 am

some are built that way and some are built with a spring to allow for reseating.
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Unread postAuthor: jackssmirkingrevenge » Thu Feb 09, 2012 12:54 am

In short, if you want pop-pop-pop-pop, you need to be feeding air into a tank at a slightly slower rate than the pop-off can empty it.
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Unread postAuthor: Major Collins » Thu Feb 09, 2012 4:38 am

jackssmirkingrevenge wrote:In short, if you want pop-pop-pop-pop, you need to be feeding air into a tank at a slightly slower rate than the pop-off can empty it.

how do i do this ? smaller ports to reduce flow?

has anyone played around with this particular type of pop off ?

http://www.ebay.com.au/itm/80-PSI-AIR-C ... 814wt_1110
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Unread postAuthor: al-xg » Thu Feb 09, 2012 4:47 am

You could also make something like this:

Image

http://www.youtube.com/watch?v=ulpI900Rhz4

The air from the tank is fed into the inlet of the pop-off valve, the oulet of the pop-off valve is fed to the pilot volume, and the threaded port of the pop-off valve is also connected to the pilot volume.
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Unread postAuthor: Major Collins » Thu Feb 09, 2012 5:10 am

hrmmmm looks quite good. I do like how its more efficient but with my lack of resources could prove a bit challenging to make
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Unread postAuthor: al-xg » Thu Feb 09, 2012 7:13 am

Yeah, the drawing does not reflect practical solution for manufacturing.


JSR has made many similar systems with some bits of tube and epoxy resin.
I reckon one could even make a copper pipe/brass fitting/soldered version also.
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Unread postAuthor: jackssmirkingrevenge » Thu Feb 09, 2012 8:28 am

al-xg wrote:JSR has made many similar systems with some bits of tube and epoxy resin.


and rubber bands and lollypop sticks...
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Unread postAuthor: Major Collins » Fri Feb 10, 2012 3:07 am

looking at the pop off al-xg posted i though it would be a little difficult to fit onto an airgun without it being awkward due to the air inlet and outlet so i threw this sketch together of an inline popoff based on the previous one... any flaws?

Image
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Unread postAuthor: Gun Freak » Fri Feb 10, 2012 6:29 am

How are you going to get the spool in the body?
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Unread postAuthor: Major Collins » Fri Feb 10, 2012 6:43 am

i would make these 1/4 threads... i could probably tap one side ,insert the spool and spring and then add the nipple and then solder it in
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Unread postAuthor: al-xg » Fri Feb 10, 2012 8:50 am

Yes there is a problem, the piston isn't balanced.

The air from the tank will be pushing the piston to the left helping the spring.
Because it has a larger area to push on than the pilot side , the pop-off valve will never fire.
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