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Pressure chamber size?

#1 User is offline   yennepnollad 

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Posted 22 October 2011 - 11:32 AM

I am trying to make a sort of nerf air cannon using pvc and a cheap chinese made solenoid valve. The first time I tried to pump it up, I could hardly push the foot pump at all only after like 3 pumps. I then replaced the solenoid valve with a ball valve, but I still couldn't get any pressure. Here is the link to the solenoid valve I bought. I am guessing that the volume of my pressure chamber is too small, but I would like this community's feedback before I try anything else.

Here is the current set up:

Posted Image

Posted Image
"How come the dove gets to be the peace symbol? How about the pillow? It has more feathers than the dove, and it doesn't have that dangerous beak."

#2 User is offline   BOSS9 

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Posted 22 October 2011 - 03:39 PM

The type of trigger valve you use makes no difference in the amount of pressure you can get in (I'd switch back to the solenoid if possible). Your problem is that your pump is too large in diameter to get to a higher PSI. Remember that PSI is pounds per square inch, so the amount of force needed to get to 40 PSI (a common nerf pressure) Is much less with a 5/8" inner diameter pump (ala AT2K) than with the 1"-1 1/2" diameter I'm guessing your foot pump is. Increesing the volume would work, but you would end up with a massive, unwieldy gun. Many dual-action bike pumps can reach awesome pressures with good efficiency, I'd go with one like that while keeping the tank size you have now.

This post has been edited by BOSS9: 22 October 2011 - 03:43 PM


#3 User is offline   yennepnollad 

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Posted 22 October 2011 - 09:31 PM

View PostBOSS9, on 22 October 2011 - 03:39 PM, said:

The type of trigger valve you use makes no difference in the amount of pressure you can get in (I'd switch back to the solenoid if possible). Your problem is that your pump is too large in diameter to get to a higher PSI. Remember that PSI is pounds per square inch, so the amount of force needed to get to 40 PSI (a common nerf pressure) Is much less with a 5/8" inner diameter pump (ala AT2K) than with the 1"-1 1/2" diameter I'm guessing your foot pump is. Increesing the volume would work, but you would end up with a massive, unwieldy gun. Many dual-action bike pumps can reach awesome pressures with good efficiency, I'd go with one like that while keeping the tank size you have now.


Yeah, I think the valve wasn't the problem, it was probably the 8 dollar foot pump I bought from Target a couple of years ago. I haven't the slightest idea of how to incorporate a small pump directly into my setup, but any forum suggestions would help :D. I do have a small dual-action bike pump on my Schwinn though. I will try that tomorrow and see if that works. I still am considering adding a massive air tank onto this thing and just have the electronic trigger glued onto a back hand grip on the tank, that way the night finder can be a front gun :D.
"How come the dove gets to be the peace symbol? How about the pillow? It has more feathers than the dove, and it doesn't have that dangerous beak."

#4 User is offline   shardbearer 

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Posted 22 October 2011 - 09:34 PM

Boss9's right on this one. Try a different pump with a smaller diameter. A 1/2" pump is 4 times easier than a 1". And I dont understand what you mean by foot pump. Like this?
Posted Image

Thanks for listening to the nonsensical ravings of a lunatic madman.

#5 User is offline   238232 

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Posted 22 October 2011 - 09:40 PM

Barbed fittings and tubing are usually available from aquarium stores, that plus epoxy generally works for me for attaching anything of a funny size.

Bear in mind that the smaller the pump's diameter, the easier it'll be to reach those pressures, but it'll take more pumps to fill it up. Sounds obvious, but going to both a thinner pump and adding a larger air tank may increase the time between shots to something ridiculous. For reference, a Titan's air tank is around 320 mL and goes to 35 PSI when the pump isn't plugged. Around Sydney at least, even unplugged, singled Titans are banned. If you're just doing this for the fun of it, go right ahead, but if it's for use in an actual war you may not want to make it too powerful.

This post has been edited by 238232: 22 October 2011 - 09:40 PM


#6 User is offline   BOSS9 

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Posted 22 October 2011 - 10:06 PM

View Postshardbearer, on 22 October 2011 - 09:34 PM, said:

Like this?


I was thinking of this type. A description of the pump used would be helpful.
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#7 User is offline   VelveetaAvenger 

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Posted 23 October 2011 - 08:47 AM

Maybe I'm missing something here, but you did actually try firing it right? It's not so big that it couldn't be full after 3 pumps from the right pump.
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#8 User is offline   yennepnollad 

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Posted 23 October 2011 - 07:23 PM

View PostVelveetaAvenger, on 23 October 2011 - 08:47 AM, said:

Maybe I'm missing something here, but you did actually try firing it right? It's not so big that it couldn't be full after 3 pumps from the right pump.


Yes I did try to fire it even after 15 or so pumps. There was still no pressure to speak of. I am still working on getting a smaller diameter pump integrated into the whole thing. Any thread suggestions on the matter would be appreciated.
"How come the dove gets to be the peace symbol? How about the pillow? It has more feathers than the dove, and it doesn't have that dangerous beak."

#9 User is offline   238232 

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Posted 23 October 2011 - 08:22 PM

This may be a bit of a stupid question, but are you sure that all your connections are airtight?

#10 User is offline   BOSS9 

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Posted 23 October 2011 - 11:19 PM

View Postyennepnollad, on 23 October 2011 - 07:23 PM, said:

Yes I did try to fire it even after 15 or so pumps. There was still no pressure to speak of. I am still working on getting a smaller diameter pump integrated into the whole thing. Any thread suggestions on the matter would be appreciated.


So it fires, but does so with little pressure? And it definitely holds air? for "integrating a smaller diameter pump" you don't need to know anything special. Go to Ace or Menards and get some 1/4" OD 1/8" ID vinyl tubing, in the general plumbing section. Get any small, handheld bike pump- I personally have used this successfully- by just inserting the tubing into the schrader fitting and tightening the connector I have an airtight seal that has never failed me at any pressure. If that is not enough, some goop would solve the problem. sticking a pump on your gun could be as simple as zip ties and hot glue. connecting the tubing and tank? drill a 1/4" hole in the tank, slather with solvent weld, and insert tubing.

#11 User is offline   yennepnollad 

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Posted 24 October 2011 - 03:46 PM

View Post238232, on 23 October 2011 - 08:22 PM, said:

This may be a bit of a stupid question, but are you sure that all your connections are airtight?


Considering how much primer and pvc cement I used on each connection, I would be really surprised if it wasn't airtight. I even used a ton of teflon tape on the pvc couplers. I have already immersed the tank in water and pumped it up to see if there were any bubbles coming from any of the connections.
"How come the dove gets to be the peace symbol? How about the pillow? It has more feathers than the dove, and it doesn't have that dangerous beak."

#12 User is offline   shardbearer 

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Posted 26 October 2011 - 04:59 PM

You don't need very much primer or cement when connecting PVC. And you only want a thin layer of cement. Because the cement melts the pvc, too much cement makes a liquid pipe. You obviously dont have a glob of plastic for a tank, but you could have done something if you really put on that much cement. The tank obviously holds air though, so that can't be the problem. Just a heads up.

Your pump is the truly critical piece in this problem. What kind of pump is it?


And one other question. When you pump and then fire, is it now easy to pump again? Because if it is still impossible, then no pressure is reaching the tank. You have something blocking your tubes most likely.
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#13 User is offline   arfink 

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Posted 27 October 2011 - 09:05 AM

What I want to know is, what are you trying to fire through? That looks like a supremely awkward barrel attachment there. You have any leaks in that? Or constriction that prevents darts from firing correctly?
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#14 User is offline   iknowmy3tables 

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Posted 02 November 2011 - 02:48 PM

I hope this topic isn't entirely dead, but pneumatics is my specialty, and if you want experts on pneumatics you may want to try spudfiles.com, anyways about your problem, observing your pictures and comments you claim that you weren't able to get much pressure, but did you actually measure the pressure with a tire pressure gauge. My geuss is that nothing is really wrong you just got the wrong expectations of how it should preform.

first off, your chamber is pretty small and the ball valve is a a very slow opening valve they generally only make loud swoosh or pop sounds if you have a large chamber, don't expect a nice pop sound or anything

second the amount volume of dead space between the barrel and the valve is large compared to your chamber volume, for testing purposes why don't you unscrew the barrel attached to the night finder and make a separate barrel that screws on directly to the valve, or duct tape it on whatever

third if you bought your pump for $8 it probably is terrible and useless

forth we can't judge your success based on the number of pumps you were able to make because different sized pumps can fill your chamber in fewer or more pumps, so make sure you tell us how big the pump is

fifth what barrel are you using? 1/2"pvc or a tight fitting barrel like 1/2"cpvc, 1/2" pvc is very loose and will only work well with high volume systems your better off with 1/2"cpvc or some other tight fitting barrel

#15 User is offline   nerfnut23 

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Posted 03 November 2011 - 06:58 PM

I think your problem lies in the dead space in that arrangement. assuming that the tank is of 1 3/4" PVC it has an air volume of about.. well. 2 AT2K tanks. Maybe. that's actually quite a lot. Your problem is your routing.

Airgun pressure isn't constant like a springer's. When the spring compresses, what happens is it pushes the dart out of teh barrel as the spring accelerates, causing a relatively constant pressure. More air = more net pressure on the dart.

Pneumatic pressure at the start is far, far greater. The problem comes in with dead space. Air guns have a high nozzle pressure immediately but it drops as the dart moves. Dead space absorbs the pressure so with that arrangement at 3 pumps the pressure behind it is far far lower- useless, even.

Tilt the tank level with the NF barrel so the fill nozzle is in the back, mate the ball valve directly to the front of the tank, then you can attach a hopper, too. Problem solved.
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