Pressure

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ocusa
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Pressure

Post by ocusa » Fri Mar 10, 2006 5:58 pm

I was wondering if anyone had measured the air pressure inside thier gun/s. If you have, how high does it get? Does it vary between the models? Is there a maximum limit of air pressure in a gun?

I was just curious because I noticed people talking about the number of "pumps".

Note: I searched for psi, bar and "air pressure" in the search engine and found nothing, so if theres a massive thread somewhere please direct me to it.

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joannaardway
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Answers

Post by joannaardway » Fri Mar 10, 2006 8:01 pm

I am unaware of a thread about it, but it's nice to see that a new member has used the search engine first.

I have measured the psi in my Triple Aggressor, so I will tell you about it.

I've fitted an extra PC (see-through) to the side of my Triple aggressor, which has been check valve frozen (I'll assume you know what this is, but many new members neglect to read the main site) and I've painted a pressure gauge on to the side of it.

At a pressure of 1 atmosphere inside the PC, there is no water in it - the pressure is the same on both sides. From here on my pressures will be in the form psi above air pressure (multiply by 14.5 to get bars/atmospheres above air pressure - add one to this to get total pressure)

Earlier today I had it up to around 100 psi, and it wasn't working too bad, although the stream was breaking up quite a lot. Given that the extra PC is an old plastic bottle I'm impressed.

However before the CVF, it was working at about 75-80 psi above air pressure.

Other than with a see-through PC and a good eye for it, without a gauge it isn't possible to tell what the pressure is. The gauges on some of the older soakers are nice, but give no idea of psi.

Some people use bike pumps to pressurize water balloon launchers and some homemades, and these may have a gauge, but few have actually measured the psi of a super soaker.

There is no real limit on air pressure, but beyond a certain point, either:
  1. you can't pump any further.
  2. the gun explodes somewhere
  3. the trigger won't pull
Hasbro claims that all the Super soakers work at roughly the same psi, although I have no experience with other brands, and I wouldn't know about brand-to-brand psi.

There is no single equation for pumps to psi, as it would differ from model to model, but more pumps = more psi for a certain soaker. CPS models will reach near maximum pressure within a few pumps, but will not have a full PC for many more.

Does that help?
"Over the hills and far away, she prays he will return one day. As sure as the rivers reach the seas, back in his arms again she'll be." - Over the Hills and far away, Gary Moore

"So many people have come and gone, their faces fade as the years go by. Yet I still recall as I wander on, as clear as the sun in the summer sky" - More than a feeling, Boston

ocusa
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Re: Answers

Post by ocusa » Fri Mar 10, 2006 8:46 pm

Hehe, your spot on about new people. Although I had read some of the articles on the mainsite, I hadn't read the CVF article. I wasn't familiar with the Triple Agressor model either. I've read about both now, and I think I understand your post quite clearly. Although, I have been interested in water pistols since April 2004, it didn't turn from interest to obsession until the last two days. So, I previously (before the last two days) hadn't really bothered to check out much more than the latest models.

In response to the question at the bottom of your reply. Yes, it did help. Anyone reading your post can see that you really know your stuff. The reason I asked about the psi of the Super soakers as I read about people creating there own homemade guns using air compressors, and a quick scan of one small ac model revealed it created 125psi +. I was just wondered if pumping achieved anywhere near that figure.

Theoretically, I think you could put a gauge in a Super soaker quite easily. Depending on the model and the type of course. From what I have read I don't think it would work for the CPS models, but would work for the air pressure models. I could explain and will if you want me to. Either that or modify one of my guns and post about the success or failure.

What do you think joannaardway? are you or is anyone interested in that modification?
Last edited by ocusa on Fri Mar 10, 2006 8:53 pm, edited 1 time in total.

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joannaardway
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Post by joannaardway » Fri Mar 10, 2006 10:22 pm

Pumping with the Triple aggressors pump (about 1/2", possibly a fraction less - smaller pumps are easier to pump, but pump less water) gets next to impossible at above 100psi. At least it gets to the point that I am liable to break it if I pump much further.

Foot pumps are much tougher, and you get your wieght behind it. Air compressors can get much higher pressures, but too high and the whole thing goes wrong. Pressure rated PVC pipe can normally take a pressure differential of around 200 or more psi - however the glue is likely to fail first.

With regards to a psi gauge, I don't think that it would be massively useful - a relatively experienced user could judge it from the stiffness of the pump.
The only real reason to know the exact psi is to allow a user to evaluate the pressure of their homemade/soaker relative to others. However I am sure that creating a mod that can fit a pressure gauge to a soaker without one would be popular if well written up.

I can see ways of doing it, but any mod runs the risk of damaging a soaker, particularly if experimenting or done by an unexperienced modder.

I am not putting down your abilities, but you have said yourself that you have only joined the soaker community within the last few days. I am guessing then you are not an experienced modder - if you have performed mods before, then ignore this comment.

If you are willing and able to perform the mod and you are sure that you have thought it through completely, then by all means try it - I am not sure that I would, but I invent new (or what I believe to be new) mods quite a lot, and other members of the community are always willing to see new mods. The community needs people willing to invent - otherwise it will grow stale.

Just make sure that the pressure gauge you use can withstand water in its internals.

You are correct - with a CPS pressure gauges have to be done differently. I am not sure how CPS pressure gauges work, having never had a CPS with one. Perhaps someone else would enlighten me.

I must complement you on your grammar, punctuation and spelling - it's not perfect, but too many people seem to think that the forum is a text messaging service.

Perhaps you'd like to use the new users forum and tell us what you have in your armoury and such like?
"Over the hills and far away, she prays he will return one day. As sure as the rivers reach the seas, back in his arms again she'll be." - Over the Hills and far away, Gary Moore

"So many people have come and gone, their faces fade as the years go by. Yet I still recall as I wander on, as clear as the sun in the summer sky" - More than a feeling, Boston

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SSCBen
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Post by SSCBen » Fri Mar 10, 2006 11:07 pm

Welcome to Super Soaker Central ocusa! I hope to see you more often!

From what I know, most of the smaller XP/Max-D air pressure water guns use pressures no more than 60 PSI. There's an old website with some old Super Soaker box images that labels pressure: http://www.geocities.com/mikahw/games/g ... s/tag.html

Note that CPS has lower pressures than air pressure. That is because the CPS system used in those water guns works through the elasticity of the rubber as opposed to actual pressurization. Please note the difference. Nothing is being pressurized in rubber CPS.

In my homemade water guns, I have done calculations to approximate pressure when a pressure gauge was unavailable. Essentially, I figured out how much water I was putting in, and what volume that would compress the air to. Very detailed equations can be made to calculate that.

As for typical pressures in a homemade water gun, most people will operate at 70 - 120 PSI. Essentially, you can go as high as your compressor will go, but do not exceed 75% of ratings on the pipe and fittings used. 120 PSI would be more than enough power to do most anything you would want to anyway.

I would write a more detailed reply normally, but the Drenchenator has been working on a reply that should help you a lot, and I'll let him see what he can say. ;)

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Drenchenator
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Post by Drenchenator » Sat Mar 11, 2006 1:17 am

When joannaardway mentioned an equation for modeling the pressure after a certain number of pumps, it made me. But after a few calculations, I came up with a general equation to model the pressure for a certain number of pumps. (The result of this equation is absolute pressure, not gauge pressure. Substract the pressure of the atmosphere to get the gauge pressure.)

Image

Basically, this equation was based on Boyles Law (PV=PV) and only works for separate chamber air pressure guns (like the APH). Pa is the atmospheric pressure on Earth (1 atm=14.7 psi). Vg is the total volume of the pressure chambers and anything past the second check valve. n is the number of pumps and Vp is the volume of the pump shaft (pump volume).

The graph is a simple rational function. It has a vertical asymptote which could be described as the total number of pumps possible. The asymptote occurs at

Image

If you have a desired pressure or know the pressure at which the release check valve releases extra pressure, you can solve for the number of pumps if you set your desired pressure as the pressure in the equation and solve for n.

If you have a graphing calculator, you can type this formula in and look at the graph.

Image Image Image

Edit: Remember, this equation works only if the temperature remains constant (or close to constant). Also, this really only is a model, but a good one at best.
Last edited by Drenchenator on Mon Oct 09, 2006 10:31 pm, edited 1 time in total.
The Drenchenator, also known as Lt. Col. Drench.

ocusa
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formula

Post by ocusa » Sat Mar 11, 2006 1:23 am

I haven't slept for awhile...maybe 17 hrs so I might have to read that last post some other time. hahaha

nice work tho.
Doooooooooooooommmmmmooookkkkuuuuunnnnnnnnn!

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joannaardway
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Post by joannaardway » Sat Mar 11, 2006 10:36 am

It's good to see an equation for an APH, and I may use it if I build one.

As I check it over it seems good, but presumably using psi rather than pascals requires that the capacities be measured in cubic inches - not the most popular unit.

To convert convert ml (cm3) to cubic inches multiply by 16.4.

However, when referring to a super soaker, it can be next to impossible to know the total volume of the chambers and piping. However if one could make an educated guess...

I had the external PC on the outside of the 3XA before the check valve freeze, and it was about 75-80 psi then - however I remember now that it sounded like the check valve was operating even as the external PC was filling, and I could pump further still filling the PC - which is odd - anyone understand how this was the case?

Anyway the new limit of about 100 psi is perfectly sufficent (it gives you an idea of how tough those bottles are - however, it is quite thick - other bottles might warp)

I'm surprised the CPS psi is so low - it makes you wonder how they match up to 100+ psi weapons so well.
"Over the hills and far away, she prays he will return one day. As sure as the rivers reach the seas, back in his arms again she'll be." - Over the Hills and far away, Gary Moore

"So many people have come and gone, their faces fade as the years go by. Yet I still recall as I wander on, as clear as the sun in the summer sky" - More than a feeling, Boston

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SSCBen
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Post by SSCBen » Sat Mar 11, 2006 3:29 pm

It's good to see an equation for an APH, and I may use it if I build one.
That's a general equation that should work for any air pressure water gun with a water pump. It easily will work without modification in most every air pressure separate PC water gun.
However, when referring to a super soaker, it can be next to impossible to know the total volume of the chambers and piping. However if one could make an educated guess...
I don't think so. I myself am fairly confident in my ability to approximate or find the exact size of a pressure chamber. You can approximate the size with shapes or intermediate calculus. You also can make a model based upon the number of pumps and the pressure to approximate the total PC size. Alternatively, you could remove the PC and measure the size from there, but that requires opening a water gun. ;)
I had the external PC on the outside of the 3XA before the check valve freeze, and it was about 75-80 psi then - however I remember now that it sounded like the check valve was operating even as the external PC was filling, and I could pump further still filling the PC - which is odd - anyone understand how this was the case?
Doesn't make much sense to me either. When the check valve is operating, further pressure is prevented by diverting the extra water from the pressure chamber. It could be that the check valve was broken and sounded as if it was operating when it really was not.
I'm surprised the CPS psi is so low - it makes you wonder how they match up to 100+ psi weapons so well.
As I said several times, CPS does not operate on pressure. Thus, using units of pressure to gauge the power of a CPS system is incorrect. The rubber CPS system is based upon the force of the rubber, not any pressure. Back several years ago, people made all sorts of wild conclusions such as "CPS is so much more efficient," all of which were incorrect because CPS does not use pressure to operate.

And before someone goes "correcting" me as many want to, just because a pressure gauge attached to a CPS system gives a pressure reading does not mean pressure exists. The gauge really measures force, and it is measuring the force of the water being pushed into the gauge. Also, there will be some pressurization as always. The small amount of air in the CPS chamber will be slightly compressed, but will be insubstantial in adding to the total power. The water also will be somewhat compressed, though for our purposes, water is incompressible.

I hope that helped. :) Let me know if you are confused with anything I mentioned.

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joannaardway
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Post by joannaardway » Sat Mar 11, 2006 4:33 pm

Presumably a CPS pressure gauge somehow measures water in the chamber rather than pressure as a air pressure gauge works.

Looking at the pictures available, it appears that cylindrical CPS PCs have fill gauges which appear to work by having a bright line on the section on the end of the PC bladder which is visible through the clear plastic of the gauge. As the chamber fills and extends, the end piece shifts... at least that's what I believe. I haven't got a cylidrical PC CPS weapon, so bear with me.

Do spherical CPS PC weapons have gauges? As the force they exert is more or less constant, I'd guess that it would be extremely complicated.
"Over the hills and far away, she prays he will return one day. As sure as the rivers reach the seas, back in his arms again she'll be." - Over the Hills and far away, Gary Moore

"So many people have come and gone, their faces fade as the years go by. Yet I still recall as I wander on, as clear as the sun in the summer sky" - More than a feeling, Boston

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Crashdummy
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Post by Crashdummy » Sat Mar 11, 2006 6:26 pm

No they don't. You have to hear for sounds that let you know when it is done or feel the difference in the pump. It is easy to tell though, and if you count the pumps in your head (I do) you will be able to know roughly how full your PC is.

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SSCBen
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Post by SSCBen » Sat Mar 11, 2006 7:07 pm

I have read that a guage for spherical PC can be made with a small modification. A dowel rod is cut and modified so it is slightly longer than distance from the empty PC to the outside of the PC case. A wide stub is also put one one end. One of the holes for the air to move to and from the PC case is drilled so that it will be large enough to support holding the modified dowel. With the dowel placed in the PC so that the stubbed end is inside of the PC case, the dowel will act somewhat as a capacity gauge. Springs, rubber bands, and such also could help the gauge work better.

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joannaardway
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Post by joannaardway » Sun Mar 12, 2006 10:43 am

Wouldn't that be somewhat liable to breaking?

I can see the principle and I briefly thought around a similar idea but dismissed it.

Counting pumps is fine - but unless you can keep track of the amount of water you have fired, it is of limited accuracy.
"Over the hills and far away, she prays he will return one day. As sure as the rivers reach the seas, back in his arms again she'll be." - Over the Hills and far away, Gary Moore

"So many people have come and gone, their faces fade as the years go by. Yet I still recall as I wander on, as clear as the sun in the summer sky" - More than a feeling, Boston

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SSCBen
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Post by SSCBen » Sun Mar 12, 2006 2:38 pm

Yes it would be easy to break. Some people have said they used nails as opposed to dowel rods, with the pointed edge cut off of course. Overall, I don't think it's a very good idea, mainly because I don't have a problem feeling when the PC is full. ;)

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joannaardway
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Post by joannaardway » Sun Mar 12, 2006 5:06 pm

Well, most people know when it is full - they want to know how full it is when it isn't full.

Maybe if I think of another way I'll post it on here - I wouldn't mind something that measured how full my CPS 2700 PC was.
"Over the hills and far away, she prays he will return one day. As sure as the rivers reach the seas, back in his arms again she'll be." - Over the Hills and far away, Gary Moore

"So many people have come and gone, their faces fade as the years go by. Yet I still recall as I wander on, as clear as the sun in the summer sky" - More than a feeling, Boston

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