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High pressure hand pumps

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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Are high pressure hand pumps an alternative to bulk tanks?

Yes
5
83%
No
1
17%
 
Total votes : 6
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Unread postAuthor: psycix » Mon Dec 08, 2008 11:08 am

No, it can only run for 5mins, then it has to cool down. But i guess it would be fine for filling my really small chamber with 300-500psi pressure or so?

Where the hell did you pull that out?
I didnt talk about any specific motor yet.
If you select a proper motor, then it will not overheat.
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Unread postAuthor: Ragnarok » Mon Dec 08, 2008 11:34 am

john bunsenburner wrote:Look, i redid my calculations if you would look at the second post.

No, you've still made errors.

It would be about a 0.25 square centimetre, which is NOT 2.5 square mm - it's 25 square mm, because it's a "square" measurement, thus meaning that the normal factor of 10 between cm and mm is squared to get 100.

Next thing you've done is multiplied mm by cm. Don't multiply together different units like that.
The actual answer is 0.25 sq. cm * 60 cm = 15 cm<sup>3</sup>

You worked out your chamber volume correctly though, but the pump volume is just a tenth of your predicted volume
That means you'll need 2100 strokes to reach 100 bar.

And i am not planing to use 100bar, i am more aiming for around 50, but maybe it will be useful one day and i will regret not having build a stronger pump.

I think that you'll regret quite the opposite. By building a pump that's capable of just 50 bar, you'll be able to drive twice as much air per stroke with your weight, halving the number of strokes to any given pressure within the pump's limits.
You'd be competing with numbers of the region of 500 strokes then to reach the pump's limit.

To be honest, I'd not recommend you using more than 20 bar at least for some considerable time - and if you just built a pump that's capable of 20 bar, that's 5 times the air volume per stroke, and about 85 pumps to reach the limit.

If you expect the average 8th grader to even think this far then you surely do not spend time with 13-15year olds.

You seem to forget that I've been one. Oh, I had wild ideas, but I knew it was important to stick to my limits, mostly because I didn't want to end up dead in my early teens.

It would be really great if some one could tell me what material would withstand such pressures.

Frozen cheese, if the walls are thick enough.

Any material can withstand anything, if there's enough of it.
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Unread postAuthor: Hotwired » Mon Dec 08, 2008 11:52 am

Ragnarok wrote:Any material can withstand anything, if there's enough of it.


Generalisations are terrible things.

Nevertheless, if you go out while it's raining with a thick enough crash helmet of silver fulminate with the intention of running into a brick wall, it is absolutely guaranteed you'd take no damage whatsoever from the wall.

Common metal piping intended for material transport or loading and not some seamed decorative variety will be fine for a high pressure pump. Steel, copper, aluminium....
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Unread postAuthor: Ragnarok » Mon Dec 08, 2008 1:19 pm

Hotwired wrote:Generalisations are terrible things.

You knew perfectly well what I meant.

Obviously making a hard hat out of a sensitive primary explosive is not a good idea, whether or not it's raining.

He asked for information on materials - I was making the point that anything to contain 100 bar has to be fairly substantial.
My 200 bar rated fire extinguishers have walls a clean 1/4" thick - you need a lot to contain those pressures.
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Unread postAuthor: Hotwired » Mon Dec 08, 2008 1:56 pm

Of course I did, I was making the point on generalisations.

Ragnarok wrote:Making a hard hat out of a sensitive primary explosive is not a good idea.


Ditto frozen cheese/pump. So we're agreed there.
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Unread postAuthor: john bunsenburner » Mon Dec 08, 2008 2:06 pm

Ok then 50bar, With a lever to minimize work and time(If i am correct then if the fulcrum of the lever is 5cm away from my pump^s piston rod and the lever is 140cm long that would make me have to one thirty second of the work so i could double the piston diameter and still ahve alot less work to do). I will use a steel pipe for the cylinder and aluminium and rubber for the piston. The rod will be a steel rod(.75cm diameter?) and the lever will be made from what ever strong steel object i find that is bendable(maybe another rod or tube). Is there any flaws within my meathod or am i good so far? I know it is abit messy and out of the blue but i am just working on the rough concepts.

@rag: I, as a young teenager, want to find my limits and boundarys, I try to be safe, or i would be sitting on a car engine trying to make it power my bike pump, or i would still be trying to construct a proper fire arm.
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Unread postAuthor: Hotwired » Mon Dec 08, 2008 2:34 pm

The work needed won't be any less by using a lever, the effort per stroke would be lower but you'll be pumping a smaller volume...

It's mechanically the same as using a small bore long stroke pump as you linked in your first post. No time is being saved by using a lever.

The floor standing pump style is the easiest way to go about it.

Take your weight and use that to work out the diameter of piston you'll need to get 50 bar when all of that is on it.
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Unread postAuthor: psycix » Mon Dec 08, 2008 2:37 pm

You wont need a lever if you figure out the right diameter.
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Unread postAuthor: Ragnarok » Mon Dec 08, 2008 2:44 pm

john bunsenburner wrote:@rag: I, as a young teenager, want to find my limits and boundarys, I try to be safe.

You've been told that 50 bar is not safe for a starting project. Even 20 bar is pushing it for a starting project.

You are looking past your limits and boundaries. You do not find limits and boundaries by starting high, you find them by starting low and working up.
If you wanted to find how far you can fall without injury, what you are doing is analogous to jumping off the Eiffel tower.
What you should be doing is jumping off a wall a couple of feet high, then another a bit taller, until you reach your limit working up - not working down.

To move away from the analogy, you get told these pressure are not safe for a beginner, then tell us "Okay, I'll do something else", and the next thing we know there's another topic or post that's asking how to do the same thing you've just said you won't do.
Quite frankly, it sounds like you're making no attempt to listen.
I don't see why when we're making every effort to get you to build up experience with a less dangerous project first, you're completely ignoring us.

The science you're using is frequently mistaken, misguided, or just plain wrong, so it's clear you're not in the position to make a well informed judgement on using pressures even I with my building experience, engineering knowledge and a mind outright built for mechanics, would be VERY wary of using.

I present these errors in your post as a point that you're really really not ready for such a project, based on the huge numbers of mistakes you're making.

If i am correct then if the fulcrum of the lever is 5cm away from my pump^s piston rod and the lever is 140cm long that would make me have to one thirty second of the work

It would be 1/29th of the force, not the work. Work is exactly the same in either case, because you then have to pump 29 times further.
A lever does no more for reducing the work than does reducing the pump bore diameter. You have to then make longer strokes in order to pump the same volume.

Another thing to consider. The fulcrum has to be fixed - how are you going to get a 60cm long pump stroke with a 5cm fulcrum? Absolute theoretical maximum stroke is 10 cm with a 5cm leverage distance, and you won't even get that.

Also, in order to make that 10 cm stroke, you then have to pump the end of the lever through 2.9m. Unless you're very tall, you've got another problem.

~~~~~

As it is, as you will not take the advice given, the only way we can protect you from harm is by preventing you from getting the disjointed snippets of knowledge you're asking for, because they will be HIGHLY dangerous to you. You're not demonstrating any of the skills, experience or other required background in science that you will have to have to use said information safely, so it's rather like us handing a live hand grenade to a three year old, and the results will probably be roughly the same.

As they say, a little knowledge is a dangerous thing. The problem is that you have woefully little knowledge in subjects that are of critical importance to your safety, which means that you are just going to be a severe danger to yourself if you attempt any of these projects.

I don't want to have to take such drastic steps as talking to the moderators and admins so as to have your access to this site restricted so as to prevent you from acquiring information that you do not know how to use safely, but if you keep up your repeated ignorance of what you are being told, I will feel it my duty to do so to protect you from a very likely injury or even potentially, a fatality.

I may sound like the most extreme killjoy ever, but I assure you, I will not be doing it (should I have to) with the intent to rob you of your dreams, fun or aspirations - just out of the utmost concern for your safety.

In the mean time, I implore other users on this site to exhibit extreme caution in the information they give you, especially that relating to these high pressure projects.
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Unread postAuthor: john bunsenburner » Mon Dec 08, 2008 2:49 pm

Ok, rag, you recomend 20bar right, I will build a 20bar pump, no lever, really simple. Then a gun, really simple, hammer valve and The quick connect and check valve filly you recomended, I realize what you mean. I will do my best not to post any thing more until i am done with my gun. I think i could be mad at you right now but i find it really nice the way you are trying to care for my safety, maybe i ahve just acted like a stuborn teenager would. I am sorry, i think i talked alot and only heard my self, I seriously hope that by the time I ahve kids there will still be people like you, thanks alot for your help, i realize i have bin stuborn and most probably a little dumb, sorry. Now as said before you will soonly have the honor of commenting on my first gun, this time i will try to stay with in the do able.
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Last edited by john bunsenburner on Mon Dec 08, 2008 2:57 pm, edited 1 time in total.
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Unread postAuthor: jitup » Mon Dec 08, 2008 2:57 pm

dude, your math is off (I think, unless I am off :? )
I am still some what knew to spudding as well I am working on my 4th, 5th gun and I am FINALLY getting up to 400PSI

I know these guys might seem like they are picking on you, but they are right and they have a lot more experience than the 2 of us put together, so listen to there advice!!

I would work on building a pvc gun with a modded sprinkler valve if I were you. If you have done that, go for a pvc piston valve gun. non the less you should not try any thing above 120 - 200 max range yet. (if you are using PVC head the pressure rating, a rupture is nothing to joke around with)
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Unread postAuthor: Ragnarok » Mon Dec 08, 2008 3:18 pm

john bunsenburner wrote:I will do my best not to post any thing more until i am done with my gun.

I have absolutely no problem with you asking questions - just please stop disregarding our answers and warnings, because they are important.

If you want to ask questions about a 20 bar hammer valve gun, go ahead and ask those questions, post up your plans for us to critique, anything like that - it will still be a challenge for you, but if you can do it, then you will have at least some of the experience you need to make the concepts you want to put into action possible, but it's never good to jump in at the deep end.

For a second, consider it from our perspective. If things go wrong, the best case scenario is that you end up with a heap of broken parts and somewhat disappointed.
However, it's equally possible you end up hurt to some degree - Brian the Brain ended up injured because of the kind of pressures you were talking about, and he really does know what he's doing. We then feel it's on our heads because we gave you information that you weren't up to using.

If things go really wrong, someone will inevitably find a trail leading back to this site, and we really could do without the negative attention of newspaper headlines like "Internet site provides dangerous plans to teenagers".

I hate to be the Bad Cop, but I really don't want things to go wrong.
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