39 replies to this topic

[Galaxy613]

After my recent projects with AT2k's and dealing with big-salvo air systems, and then seeing rork's recent air blaster, it got me thinking... Why can't I make my own AT2k airtank? I know we ALL hate idea threads, but I also know that compressed air is not something sneeze as because it has a tendency to explode if not done properly, so I wanted to submit this idea before I went out and bought the parts. (Because I'm poor and can't keep a locker full a new parts ) And I WILL go out and make this after other people weigh in on this idea, and/or deem it safe.



I have actually not taken into account a nub that needs to be at the end of the rod which will push the front washers back when you pull the rod - because I DON'T know what that nub should be yet. I also didn't take into account a hole for the pump because that hole can be ANYWHERE.

Also the specifics need to be flushed out, like what size rod, what size washers and etc. but what I want to know is if this idea is feasible. I intend on glueing togeather the Endcap and the Plug with Plumber's Goop, even without glue if you hammer the two togeather it's very hard to get them apart. So I assume after I hammer them togeather AND goop them, nothing will get them apart much less a little air pressure.

This idea seems TOO simple. I've tried searching but I probably missed something.

Edited by Galaxy613, 05 December 2008 - 10:33 AM.

[Carbon]

The DCHAP-1 is somewhat similar to this idea, but it's a push as opposed to a pull (thus avoiding your centering problem).

Edited by Carbon, 05 December 2008 - 11:17 AM.

[CaptainSlug]

Why?
1. You probably can't use a rubber washer to seal against the trigger rod. The pressure will deform the center of the rubber washer and increase it's ID.
2. Getting a good sealed fit between and o-ring and the trigger rod without having tons of friction is difficult.
3. Making all of those parts from scratch in a way that results in them being leak-free isn't easy.
4. A rubber washer may not be suitable for the barrel seal either unless it's pre-compressed by a decent size spring. Even though the DCHAP-1 valve has a huge amount of surface area for pressure to work on and the fairly strong maverick spring pushing on it, the valve will still leak at lower pressures.

The AT2k tank has a captive seated o-ring sealing against the stainless steel trigger rod.
Designing and then making parts that utilize o-rings is very hard to do with basic tools.

Go ahead and try it, but frankly I doubt it will work as reliably as the 2k tank.

I intend on glueing togeather the Endcap and the Plug with Plumber's Goop, even without glue if you hammer the two togeather it's very hard to get them apart. So I assume after I hammer them togeather AND goop them, nothing will get them apart much less a little air pressure.

NO. BAD.

You can't fuse PVC parts with just a slip fit and a thread sealant. You have to use PVC cement or the resulting bond won't be able to hold pressure. No amount of hammering will allow a slip-joint between PVC to contain pressures above 5psi.

Edited by CaptainSlug, 05 December 2008 - 12:51 PM.

[slowguitarman]

Getting a fit between rod and ring shouldn't be that tough. Especially if you can get the same size o-ring that's in a AT2K tank. If you can, lubed up 3/32" brass rod works well. I use it for my pseudo-homemade AT2K air tank. It's actually more like a tank expansion, but has a lot of homemadeness to it. Maybe I'll post a pic of it before I put it in what it's going into.

Edited by slowguitarman, 05 December 2008 - 12:46 PM.

[Draconis]

Neoprene washers will not be soft enough, which is why the DCHAPs leak. You will need to use silicone. I have been working on a couple of designs for a while, though. Both this dump valve type and the piston type like JSB refers to. In my previous attempts, the biggest problem I have had is not building any pressure because the valve leaks. So I am still searching for O-rings or gaskets which are soft enough.

[Split]

I had done some research on a similar project, and for the shaft seal, I doubt a lubed o-ring will cut it at all.

Try this: 9281K144
Couplered with this shaft: 6061K431
Or you can find whatever combination you like for the sizes, but those are the two I was going to use, until I realized how much the project was going to cost (much more than the cost of a NIB 2k). I'm pretty sure the sealing nub on the front is going to be pretty difficult and take a lot of browsing, but I don't doubt it can be done.

Bob, have you tried looking for "back pressure valves?"

[CaptainSlug]

I don't mean to hijack the thread, but since the Big Salvo was mentioned from the start, I'd like to know if there is any significant body of work here on NH on the topic of piston type homemade valves. Like the valves used in SSPB, TS, Hornet, BigSalvo, SMDTG, etc., etc.

They're called Quick Exhaust valves, but the off-the-shelf models have a poppet that won't actuate below 8 psi.
I tried making one with PVC parts, but it wasn't workable because the poppet needs to be very light weight and small so that it can actuate at a very low pressure.

Just dissect a hornet valve at look at the parts inside. Good luck duplicating them easily.

Edited by CaptainSlug, 05 December 2008 - 04:02 PM.

[Draconis]

Try this: 9281K144
Couplered with this shaft: 6061K431
Or you can find whatever combination you like for the sizes, but those are the two I was going to use, until I realized how much the project was going to cost (much more than the cost of a NIB 2k). I'm pretty sure the sealing nub on the front is going to be pretty difficult and take a lot of browsing, but I don't doubt it can be done.

Whoa... 1/2"? Frick-on-a-stick, that's kinda big, don't you think? It would be easier to use something like a standard Honda valve stem seal. They are made for linear use, and for something like 6-7mm shafts. And cheap. I have 30-40 that I'd be willing to sell very inexpensively. Like $0.25 each or something.

[Draconis]

Whoa... 1/2"? Frick-on-a-stick, that's kinda big, don't you think? It would be easier to use something like a standard Honda valve stem seal. They are made for linear use, and for something like 6-7mm shafts. And cheap. I have 30-40 that I'd be willing to sell very inexpensively. Like $0.25 each or something.

I think he picked 1/2" because the other sizes are more expensive. And as you note, those seals are meant for rotational use, not linear. The valve guide seal idea may be a good direction to explore, but internal combustion valve seals generally will not hold much of anything over tens of seconds.

Well, now... I suppose that might possibly be a problem. I may just try it, though. Heck, maybe I will use an old intake valve too.

[rork]

On topic: I actually like this design a lot. No way would that rubber washer (the rear one particularly) work, but that shouldn't be the focus, as there are ways to get around that. Actually, you've given me some ideas...

[Split]

I used 1/2" because I was making a homemade dual action pump. Hence me saying that you can change the sizes. Bob, these do work for linear sealing, though they're not rated for it (per the email I received in response to my question about it). I think you're getting confused with the dozen other pages of seals that are strictly for rotational use. Your speculation gets no where.

Where did Galaxy go in all of this?

Edited by Splitlip, 05 December 2008 - 06:51 PM.

[imaseoulman]

I've been pondering all the questions asked in this thread for years now. I've never made a homemade...but that's all about to change...soon. It will be a "back pressure valve" made from easy to obtain parts. I actually acquired a necessary part TODAY that I haven't been able to find for a while. This is what I was hinting at in the PixieBlast thread. I haven't built anything yet, so I don't know for sure that it will work, but I'm fairly confident that it will.

The firing pin pull method is very unlikely to work. If you look closely at an AT2K tank, you'll notice that the seal at the base of the tank is actually housed in a small compartment off of the main tank. It would be very difficult to get a good seal in place using just an endcap. Good luck.

[Galaxy613]

Thanks for the LOADS of input. And thanks a ton for your input CS, I was really hoping for your input especially. I really wish I could've had access to the internet at work, because now I need to have a long post to reply to every one. lol

1. You probably can't use a rubber washer to seal against the trigger rod. The pressure will deform the center of the rubber washer and increase it's ID.

Partly inspiried by Rork's post, could I keep the finishing washer and put goop on the side that'll touch the PVC and use Goop as the seal? Because we fix AT2k's rear seal by spraying slicone on the shaft and gooping it, could I use that INSIDE the tank? Or will it not be flexible enough or will melt under pressure?

2. Getting a good sealed fit between and o-ring and the trigger rod without having tons of friction is difficult.

O-Ring? I never mentioned an O-Ring? >.>

3. Making all of those parts from scratch in a way that results in them being leak-free isn't easy.

I will have to take your word for it. and Draconis's.

4. A rubber washer may not be suitable for the barrel seal either unless it's pre-compressed by a decent size spring. Even though the DCHAP-1 valve has a huge amount of surface area for pressure to work on and the fairly strong maverick spring pushing on it, the valve will still leak at lower pressures.

I have this pretty powerful 15/32'' OD, 3/8'' ID spring that I could use that would DEFINITELY keep the front rubber washer compressed... If I even wind up using any rubber washers.

The AT2k tank has a captive seated o-ring sealing against the stainless steel trigger rod.
Designing and then making parts that utilize o-rings is very hard to do with basic tools.

That is why I was designing this around rubber washers...

It's actually more like a tank expansion, but has a lot of homemadeness to it. Maybe I'll post a pic of it before I put it in what it's going into.

PLEASE do!

Where did Galaxy go in all of this?

Went off to work for 9 hours. @.@ Helping my piano teacher make end-of-year music CD's for all 90 of her students.

Hmm. I will definetly have to think and plan about this some more. But I think I can do it... off to ACE Hardware!

[roboman]

I don't mean to hijack the thread, but since the Big Salvo was mentioned from the start, I'd like to know if there is any significant body of work here on NH on the topic of piston type homemade valves. Like the valves used in SSPB, TS, Hornet, BigSalvo, SMDTG, etc., etc.

I'd really appreciate a few links or even suggestions what to search for, rather than to divert this thread away from sleeved-pin valves. I too was unable to solve the sleeve sealing problem in a way suitable for regular folks to make copies. But I still hope someone can.

By the way, I did build one where the sleeve was eliminated by using a solenoid to pull the valve open. Really cool, very effective, and at that time, the parts could easily be bought mail-order. Anyone who likes spending $50 and carrying around six D-cells (e.g., a Vulcan) might like my idea ... yeah, exactly my conclusion -- maybe for spudguns, but not practical for nerf.

I think this might be what you're looking for. The inline valve could probably be built for $20-30, and it would have a much better flow rate than a QEV. I think there was a thread on spudfiles about making an inline piston valve from an empty deodorant can. While that may be a little big for nerf guns, it could certainly be scaled down to the size you need.

Edited by roboman, 05 December 2008 - 10:30 PM.

[Doom]

I've done some similar work in the past, but the project was not finished. My valve was very similar to Dr. Nerf's valve (those photos are no longer online but some of them are available here). What others have called the sleeve didn't seal well because sch. 40 PVC pipe doesn't have a diameter of 1 inch (I should have known this). This caused me to reevaluate the entire project and I scrapped it (I think--it might actually be in a box somewhere).

I did upload some photos from this project to my webspace, but I won't link to them because this gun was a piece of crap. The two things I learned are don't try to make your own valves unless you have precision equipment and keep everything small and light.

Another thing: If you don't want to permanently fuse the two fittings, you could use a rubber gasket and screws to make sure the fittings seal and can be separated. I have seen this done successfully before in spud guns.

A modified hose handle would probably suit you well, if not, smaller QEVs are worth looking into too. Some small solenoid valves used in things like washing machines might be worth considering too, but I've only read about their use once.

Edited by Doom, 05 December 2008 - 10:46 PM.

[Galaxy613]

I think a Solenoid is a tad overkill for this project. I really want to make something like a AT2k chamber that is extremely portable, reliable, and cheap. A solenoid will only leave the 'reliable' there.

[Doom]

The solenoid valves used in things like washing machines, dish washers, etc., are cheap (like $4) and small from what I've read about them. That's why I suggested those kinds of them. Edit: The guy in this link bought one for $4.50.

I was not talking about solenoid sprinkler valves which are rather large for Nerf.

Let me reiterate that I've only read about small solenoid valves' use once in the link above. They seem appropriate because of their small size and low cost. Someone with more free time than myself should investigate them.

Edited by Doom, 06 December 2008 - 08:38 AM.

[DTReaper]

I actually tried to make a 2K tank homemade but failed. There were to many leaks despite many strong springs on it. I tried to sleve aluminium piping into each other due to the smaller sizes it came in at my local hobby store but even with tightening rings it still didnt seal properly. Good luck with it if you choose to go forward with the plan.

-DTR

[CaptainSlug]

To summarize my previous post in one sentence: Rubber washers don't work very well for sealing air, because (unlike o-rings) they're only meant for sealing when under a heavy compression load.

[imaseoulman]

I just wanted to add that I did some preliminary proofs of concept today and it looks promising.

[Doom]

imaseoulman, could you explain your concept? It sounds interesting.

Back pressure valves are a form of check valve. I'll make a guess that you're going to manually push/pull the check to open the valve. That should work. I've actually thought of this before but never did anything with it so this was the first thing to come to mind. The problem with this is finding a reliable way to push the check.

Edited by Doom, 07 December 2008 - 05:56 PM.

[Galaxy613]

Back pressure valves are a form of check valve. I'll make a guess that you're going to manually push/pull the check to open the valve.

Hmm I didn't feel I needed to clearify that, but yeah. the point of the extra rod sticking out the rear is so you can PULL on it and it will open the front of the airtank. The only problem is, I don't know how exactly it will open the front valve.. I don't know if super glueing a thick metal washer would work. And that metal washer will push on the front rubber washer and the front finishing washer, the finishing washer will be constantly pushed on by the spring. I am only worried about the glue failing..

*EDIT* Or! We could use a long nail with a flat head..

*DOUBLE EDIT*

To summarize my previous post in one sentence: Rubber washers don't work very well for sealing air, because (unlike o-rings) they're only meant for sealing when under a heavy compression load.

Would a heavier spring make it work better?

I too are very interested in imaseoulman's tests..

Edited by Galaxy613, 07 December 2008 - 06:56 PM.

[Doom]

Hmm I didn't feel I needed to clearify that, but yeah. the point of the extra rod sticking out the rear is so you can PULL on it and it will open the front of the airtank. The only problem is, I don't know how exactly it will open the front valve.. I don't know if super glueing a thick metal washer would work. And that metal washer will push on the front rubber washer and the front finishing washer, the finishing washer will be constantly pushed on by the spring. I am only worried about the glue failing..

I know what the rod is for. As I said, I've worked with similar things in the past.

I'm not sure what you mean "I don't know how exactly it will open the front valve." Are you unsure how to attach the seal part to the rod? I used threaded rod for that in the past and it could work here too if you use something like a partially threaded bolt.

Would a heavier spring make it work better?

The seal should already be under a load from the pressure. The easiest thing to do would be making the sealing face and inner diameter of the outer pipe larger, which would increase the force applied by the basic rule F = P*A. Using a stronger spring works too, but it'll be a little more expensive.

Valves of this type can very easily become too difficult to pull if the spring is too strong or the sealing face is too large. Watch out for that.

[Galaxy613]

I'm not sure what you mean "I don't know how exactly it will open the front valve." Are you unsure how to attach the seal part to the rod? I used threaded rod for that in the past and it could work here too if you use something like a partially threaded bolt.

Couldn't we get a partially threaded bolt, and get two nuts to sqwish a O-Ring between them and THAT can seal the front? We'll have to threadlock/superglue the nuts so they don't sqwish the O-Ring too much.

Edited by Galaxy613, 07 December 2008 - 07:13 PM.

[Doom]

O-rings can stretch a good deal so I'd imagine tightening the nuts wouldn't do any good.

If you want to make something like this, use a partially threaded bolt with a rubber washer and fender washer behind it on the threaded part. Tighten the two with a nut, using a small washer on the front if possible. On the non-threaded size put an O-ring of correct dimensions and have a way to hold that O-ring on in the valve assembly. A return spring will finish the rod part. This was essentially what I did on my similar project I mentioned earlier. Let me reiterate that after thought I decided this was too much work.

Edited by Doom, 07 December 2008 - 07:23 PM.