23 replies to this topic

[Gutzenheim]

Hey everybody, I'm kind of new to the web site and I've done quite a few modifications in the past, but almost immediately wanted to make homemades. This is my first gun and I'm actually posting my second gun as another thread immediately after I post this. I use a rainbird 3/4 inch sprinkler valve, 2 9 volt batteries and a momentary switch to create my trigger.



Here's a torn apart pic of the gun.





Here's a constructed pic of the gun with the normal dart barrel.




http://i258.photobuc...er/IMG_8529.jpg

Here's my lovely wiring. It's just a simple series circuit.





Here's a side by side barrel comparison pic that shows the ball attachment and the dart attachment.

http://i258.photobuc...er/IMG_8547.jpg

Hooked to an air compressor.



I've had some questions on wiring so here's an explanation of how it's done.


I'm sorry, but I can't give you stats as far as distance and those things go at this point in time because I don't have a long enough range to fire it yet and it's very cold outside here now. I will, though when given the chance do all my official testing. I will however say that it does indeed rock a nerf dart at only 50psi and splits them at 100psi. I hope you like my first gun and view my 2nd gun which should be on here either today or tomorrow.
~~Gutzenheim

Edited by Gutzenheim, 08 March 2008 - 08:49 AM.

[Carbon]

That's nice and clean looking. Er....you did glue it together, right? Not used to seeing air pressure homemades that don't look like they got into a fight with a jelly sanddwich. Anyway, check into modding your sprinkler valve...it opens faster, and you don't need batteries.

Nice first post...looking forward to seeing more work.

[Gutzenheim]

Yes, I glued it using an all purpose cement (don't be scared) where one of the uses for it is pvc. It does a great job holding air pressure...I have no leaks that I know of. The cement is actually found in the plumbing section of my hardware store (menards). I just did the best i could of not smearing it everywhere; also a good thing to do is when putting the pieces together using the cement twist the pieces as you put them together, it helps. Also, my brother is an apprentice pipe fitter by trade so he gave me some tips on gluing all the parts and such. If you have any questions feel free to ask.

[CaptainSlug]

Actual PVC Cement =/= anything else
Actual PVC Cement is clear, syrupy, and smells terrible. The the label says it's good for anything other than PVC then it's not really PVC cement.

Edited by CaptainSlug, 09 March 2008 - 07:54 PM.

[Gutzenheim]

Yes captain, I believe that's actually what I used, I just couldn't remember the label at the time, sorry for my mistake.

[aetherguy881]

*Takes note of no pvc primer being used*
*Takes note of pvc glue lid off (from that angle) and one hand cut off near face/nose*

What pressures do you intend on attaining whilst using this? I don't like hearing about when people use pressures higher than 40-50 psi without pvc primer (purple liquid). I am concerned for you because of this, especially since you're using a compressor. Will you regulate it? I've attained just over 100 psi with a full sized bike pump. All in the matter of safety.

How ventilated is that fancy room there? I don't think Mommy would like to have that in the kitchen/dining room.

I'm just swinging at you, just simple and joking questions. I hope you like the sprinkler valve. They're great!

[Gutzenheim]

Ok guys, I didn't use primer, but my brother is an apprentice pipe fitter and has said nothing about safety problems and he knows how it was built. Plus, I've taken this gun over just at 100 psi before and it didn't explode. This is oatey pvc cement and the lid is indeed on in the picture, the only reason it appears not to be in the picture is that you can see the lid threading on the outside of the lid. Also, this picture was taken in my basement, not my dining room. And my mommy didn't mind me working on it there.

Edited by Gutzenheim, 10 March 2008 - 03:24 PM.

[Carbon]

Sorry if we appear to be harping on primer and safety, but that's because PVC isn't rated for gas pressure: those ratings on the tube are for liquid only. That, and when it fails, it tends to fail explosively (and with shrapnel). Because of that, safety precautions are a good thing...and that means PVC cement with primer.

[imaseoulman]

How fast does the valve open? I've been in the design process of my first homemade for quite some time and I keep coming back to the solenoid issue. Is there a noticeable delay between the time you depress the trigger and the dart leaving the barrel? Also, where did you get your toggle switch and how much was it?

[Gutzenheim]

How fast does the valve open? I've been in the design process of my first homemade for quite some time and I keep coming back to the solenoid issue. Is there a noticeable delay between the time you depress the trigger and the dart leaving the barrel? Also, where did you get your toggle switch and how much was it?

The valve opens and the dart leaves the barrel almost as quickly as I depress the trigger. Also, I'm not using a toggle switch, I'm using a momentary push button switch that cost me about $3.00 at my local radioshack. I like using a momentary switch over using a toggle because as soon as I let off the trigger the valve closes again as long as you're using a normally closed valve. This allows for the tank to be pressurized quickly afterwards.

[aetherguy881]

Just because it held that time doesn't mean it won't hold. The primer cleans the pipe and readies it for the chemical break down and reconstruction. When you seal the separate pieces of pipe, you are literally creating one piece of pvc out of many. You are effecting the molecules of the pipe, unlike what Gorilla Glue, super glue and epoxy (just to name a few) do.

If that's your basement, wow! That's nicely finished. You don't have a shop or a garage to do any of this? What about outside?

The valve is a sprinkler valve. The valve mechanism is a diaphragm and is actuated by the solenoid (the electrical part). Inside the solenoid there is a relay or coil that quickly opens the space above the diaphragm thus creating an imbalance of pressure which opens the valve. If I can find an animation I will be glad to link to it. I just don't remember where it is off the top of my head.

Granted they're much more expensive than ball valves, they're much more efficient and reliable to use. They also dump much more air into the barrel at one time.

[Gutzenheim]

Just because it held that time doesn't mean it won't hold. The primer cleans the pipe and readies it for the chemical break down and reconstruction. When you seal the separate pieces of pipe, you are literally creating one piece of pvc out of many. You are effecting the molecules of the pipe, unlike what Gorilla Glue, super glue and epoxy (just to name a few) do.

If that's your basement, wow! That's nicely finished. You don't have a shop or a garage to do any of this? What about outside?

The valve is a sprinkler valve. The valve mechanism is a diaphragm and is actuated by the solenoid (the electrical part). Inside the solenoid there is a relay or coil that quickly opens the space above the diaphragm thus creating an imbalance of pressure which opens the valve. If I can find an animation I will be glad to link to it. I just don't remember where it is off the top of my head.

Granted they're much more expensive than ball valves, they're much more efficient and reliable to use. They also dump much more air into the barrel at one time.

Thank you for the info on the pvc primer, nicely done, I do have a garage I do lots of the work in, I simply took the pictures in my basement because it was a nice atmosphere and that's just where we decided to glue it. I know what your point is about it being dangerous and I understand these dangers. Thank you for the warning shot though, I don't use it at pressures higher than about 50 or 60 psi, but I have taken it up to 100 before, but probably won't again because there's no need to and it split darts at this pressure. As far as the sprinkler valve info goes thank you, I understood these things and the operation of them, but it was a nice bit of info for anyone visiting. I'm sorry if I sounded angry before, but your original posts weren't put in a friendly manner, so I'm sorry, no hard feelings man.

[Shadow 92]

Sorry if we appear to be harping on primer and safety, but that's because PVC isn't rated for gas pressure: those ratings on the tube are for liquid only. That, and when it fails, it tends to fail explosively (and with shrapnel). Because of that, safety precautions are a good thing...and that means PVC cement with primer.

What's the difference between liquid pressure and gas pressure? I mean if you have a liquid at 25 psi and a gas at 25 psi then that means they're both exerting 25 pounds of pressure per square inch. I don't get why it wouldn't be rated for both liquid and gas? The only possible explanation is that air pressure more easily fluctuates with temperature than liquid. And if that's the case, I don't see why it isn't safe to take PVC rated to 120 psi to 100 psi (assuming that it is glued properly). Unless you fill the air tank outside in the snow and then bring back inside to your house with the temperature set to 90, I don't think that you could raise the pressure enough by an increase in temperature to cause it to explode with a 20 psi buffer.

EDIT: nice gun. I like the airtank's extension into the foregrip. Have you ever considered using a blow gun trigger to pilot the solenoid?

Edited by Shadow 92, 10 March 2008 - 11:30 PM.

[Gutzenheim]

Ok guys, lets clear the air on the pressure. I believe gas and liquid pressure to be the same because If you ever take an engineering course (I currently am) they'll tell you that gasses are considered liquids. Plus, to me a pound per square inch is a pound per square inch, I'm with shadow on this one. Also, why and how do you think they hydrotest hpa tanks.

Edited by Gutzenheim, 11 March 2008 - 05:16 AM.

[aetherguy881]

Pressurizing pvc in the snot is a bad idea all together. You just thought about the gas properties. You failed to take the pvc's properties into consideration. When pvc gets cold it gets significantly brittle from when it's at room temperature. The pvc just doesn't have the stretch as it did when it was warmer.

I don't recall the properties of abs. Although that's usually left for basic combustion spudguns, not pneumatics.

[Carbon]

Ok guys, lets clear the air on the pressure. I believe gas and liquid pressure to be the same because If you ever take an engineering course (I currently am) they'll tell you that gasses are considered liquids. Plus, to me a pound per square inch is a pound per square inch, I'm with shadow on this one. Also, why and how do you think they hydrotest hpa tanks.

If you don't believe me, then believe OSHA. PVC pipe is not supposed to be used for above ground pressurized gas transport....that's not its intended purpose. This is not because it can't do it, but because if it fails, and it's above ground, it will detonate like a fragmentation grenade.

An excerpt from the above link that sums things up:

"The main problem with using PVC pipe and fittings for compressed gas is not that it spontaneously explodes but that PVC is a brittle material that can be broken or shattered with external force unless properly protected. Compressed gasses can be best described as being analogous to a coiled spring. When a PVC pipe or fitting fails when under stress from compressed gas it literally explodes like a bomb, sending shards of plastic flying several feet in all directions. Liquids, on the other hand, being compressed by only 1/10th of 1% contain very little stored energy. When pressurized systems with liquids fail, the energy is dissipated very quickly, thereby creating a much lower potential for hazard. "

In other words, they hydrotest HPA tanks because it's a helluva lot less dangerous than using air.

Edited by Carbon, 11 March 2008 - 11:33 AM.

[Doom]

I've worked with both compressed air and water and they are definitely different. To reiterate much of what Carbon said, it comes down to expansion, not necessarily the force the pressure makes (which is the same). Gases expand significantly more, so when the pipe fails it will explode like a bomb. If a liquid causes a pipe to fail, it'll most likely crack in one spot just because there wasn't much if any expansion. If you get into gases plus liquids, it could be either or both depending on a number of factors. Any of the three situations I just mentioned aren't great, so it's best to avoid them all together. Use primer, use the right cement, make sure your primer and cement aren't too old, give the pipe ample time to cure at the right temperature, etc.

And for the record, I'm an engineering major myself and I've never heard anyone say that gases are liquids. Liquids and gases are fluids.

[Gutzenheim]

ok guys, I wasn't trying to prove anyone wrong, I was just stating what I thoguh, thank you for the knowledge, I appreciate it

[jwasko]

Not saying that liquids and gases are the same (they're definitely not, particularly on a molecular or atomic scale; see the Kinetic-Molecular Theory), but you're probably thinking about fluid mechanics, Gutz-man:

According to the fluid mechanics article in the Wikipedia, "Fluid mechanics is the study of how fluids move and the forces on them. (Fluids include liquids and gases.)"

I don't know much (if anything) about fluid mechanics, but from what I've read in this thread I'm guessing the the similarities between gases and liquids end at compression and pressure.

As a side note, it is very interesting to think of gases as a very compressible spring, and liquids as a spring that only gets compressed slightly....

*thinks about the implications*

Edit: And now that I read Doom's post again, I see that he already mentioned the fluids part. Thus my post is rendered at least partially unnecessary.

*but if A=C and B=C, does not A=B?*

Edited by jwasko, 11 March 2008 - 02:30 PM.

[d0nk3y k0n9]

*but if A=C and B=C, does not A=B?*

No, A=/=B because C is a category, not an actual thing, so transitive property doesn't apply. Also, it really isn't A=C and B=C, its A is a subset of C and B is a subset of C.

Both gasses and liquids are considered fluids, so they share some properties. However, because they are separate subcategories, they also have some properties which are different.

[Doom]

ok guys, I wasn't trying to prove anyone wrong, I was just stating what I thoguh, thank you for the knowledge, I appreciate it

No one's thinking you were proving anyone wrong, rather, they're just correcting you so you can continue to enjoy Nerf without death/injury. Proper safety procedures in building any pressurized device are important. I have read a lot of things that have gone wrong and I wouldn't wish them on anyone.

[Gutzenheim]

ok guys, I wasn't trying to prove anyone wrong, I was just stating what I thoguh, thank you for the knowledge, I appreciate it

No one's thinking you were proving anyone wrong, rather, they're just correcting you so you can continue to enjoy Nerf without death/injury. Proper safety procedures in building any pressurized device are important. I have read a lot of things that have gone wrong and I wouldn't wish them on anyone.

Well, thank everyone for the info, however I realize this is a dangerous gun and I view and recognize every pressure vessel I deal with as dangerous. It's nice to know everyone cares so much about me. Ha! I understand the difference between the pressure thing because of volume, density, and things of that sort, but I still have to say that one pound per square inch is still 1 pound per square inch in my mind, but I recognize what you mean and greatly appreciate the contributions. Also, I wasn't that I didn't believe anyone I just questioned it based on prior knowledge, but now realize what you mean. And yes, I was referring to fluid mechanics, sorry for any confusion and I hope we all continue to play it safe and try to warn people about the issues with pressure differences and things of the sort. Thank you all!!

~~Gutzenheim

Edited by Gutzenheim, 11 March 2008 - 07:26 PM.

[Shadow 92]

Pressurizing pvc in the snot is a bad idea all together. You just thought about the gas properties. You failed to take the pvc's properties into consideration. When pvc gets cold it gets significantly brittle from when it's at room temperature. The pvc just doesn't have the stretch as it did when it was warmer.

I don't recall the properties of abs. Although that's usually left for basic combustion spudguns, not pneumatics.

I never said I pressurized a cannon in the snow. I was merely using it as an extreme example to demonstrate the rare occurence when a temperature change would result in the explosion of PVC pipe due to an increase in temperature.

"The main problem with using PVC pipe and fittings for compressed gas is not that it spontaneously explodes but that PVC is a brittle material that can be broken or shattered with external force unless properly protected. Compressed gasses can be best described as being analogous to a coiled spring. When a PVC pipe or fitting fails when under stress from compressed gas it literally explodes like a bomb, sending shards of plastic flying several feet in all directions. Liquids, on the other hand, being compressed by only 1/10th of 1% contain very little stored energy. When pressurized systems with liquids fail, the energy is dissipated very quickly, thereby creating a much lower potential for hazard. "

In other words, they hydrotest HPA tanks because it's a helluva lot less dangerous than using air.

Okay, I get it. I always thought that people said that because they believed that PVC would be more likely to fail because a gas was being used as opposed to liquid, for which it is rated for. I understand now that PVC can handle 100 psi (depending on the size), but if it were to exceed the pressure rating then it would fail catastrophicly as opposed to simply leaking.

Wow, this turned into a very informative debate. Usually someone gets butt hurt and starts yelling (or typing agressively ) but this was surprisingly pleasant. I learned a lot. Why can't all topics be like this?

Edited by Shadow 92, 11 March 2008 - 10:55 PM.

[Carbon]

I understand now that PVC can handle 100 psi (depending on the size), but if it were to exceed the pressure rating then it would fail catastrophicly as opposed to simply leaking.

There’s a few more things to consider, based on the non-standard ways in which we use PVC:

PVC is intended to be buried/in walls/out of the way. Because it’s inherently brittle, a sudden blow can cause PVC to fail, even if it’s below rated pressure. Also, UV light weakens it, and makes it even more brittle.

Just a few more reasons to keep it well below the rated PSI.

Wow, this turned into a very informative debate. Usually someone gets butt hurt and starts yelling (or typing agressively ) but this was surprisingly pleasant. I learned a lot. Why can't all topics be like this?

We try, we try.