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A water rocket is a type of model rocket using water as its reaction mass. The pressure vessel (the engine of the rocket) is constructed from thin plastic or other non metallic materials (usually a used plastic soft drink bottle) weighing 1,500 grams or less. The water is forced out by compressed air. It is an example of Newton's third law of motion.

Compressor Certification

Discussion about Compressors, hose, pipes, fittings, launchers, release mechanisms, and launch tubes.
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tsumrall
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Compressor Certification

Post by tsumrall » Tue Aug 28, 2007 10:33 am

Who certifies the compressors as being safe for human proximity. This becomes even more important when people start trying to adhoc this together.

I use a nitrogen bottle: tested, xrayed, and certified for safe human proximity.

Can you say the same for your compressors? If not, think safety!



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Re: Compressor Certification

Post by WRA2 Admin » Tue Aug 28, 2007 8:20 pm

tsumrall wrote:Who certifies the compressors as being safe for human proximity. This becomes even more important when people start trying to adhoc this together.

I use a nitrogen bottle: tested, xrayed, and certified for safe human proximity.

Can you say the same for your compressors? If not, think safety!
The purpose of the compressor rule is mainly to insure that air is used for the rocket launch and not some other more highly compressable gas like CO2. We want all teams using the same energy storage medium as well as the same reaction mass. Requiring the air be compressed at the launch site insures that teams living in places where special permits are required to transport pressurized gasses are not at a disadvantage. We also discourage the use of bottled gasses because no amount of certifications and x-ray testing will prevent someone from poisoning themselves by leaving a valve open accidentally. Not to mention the harm to the environment caused by the release of greenhouse gasses like CO2.

We feel that a team capable of building a safe rocket that can withstand high pressures should also be capable of building a method to compress the air to fill it. This is part of the engineering required which makes the competition more challenging. In most cases using tanks to supply higher pressures encourages illegal modifications to (or removal of) safety equipment, which we do not condone. By constructing a pressure source no safety laws are broken. High pressure compressors are commercially available and are acceptable under the rules. We require that all teams be responsible for their own safety and build with safety margins in all their designs, including the launcher and pressure source.


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Post by rockets42 » Tue Aug 28, 2007 11:40 pm

what about scuba tanks? They are certified, you need to be licensed to get one refilled, they will only refill it with breathable air from the atmosphere using a compressor. There is nothing poisonous in it, and does not pollute the environment. Its just a convenient way of storing air.

If a compressor has any form air storage cylinder isn't that the same thing?

In terms of concerns for CO2 being released into the atmosphere that is true that we shouldn't do it. But doesn't running a compressor just produce CO2 at the power station?



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Post by Drag_Racer408a » Wed Aug 29, 2007 8:15 am

The main thing that i think the WRA2 is concerned about is the handling of the compressed gas. If you drop the tank it could fail and could be faital because of the large amounts of pressure inside.

If you pump on site with a portable air compressor then the only thing under pressure is the rocket and hose. And with the WRA2 rules you have to be 50 feet away from the rocket.

Also with a portable air compressor they sort of give a "Limit" on what pressures you can use. It prevents people who don't know what they are going with compressed gasses not get hurt.

And it would be too easy to just use a SCUBA tank, out hook it up and pressurize the rocket within 30 seconds and go.

Finally you can get a pretty good amount of pressure out of a little air compressor too. I have one that goes to 250 PSI and i haven't been able to make a rocket to even operate at these pressures. My end caps have a little issue.

Maybe one thing that the WRA2 could do is have levels of operation. I know that the Pyro rocket community has several levels. It could be like after your break 1000 feet then you could use SCUBA tanks because you have already handled high pressures. It would be better than having a noobie come in and just ram up the pressure and could get hurt.

Maybe it would just be too much to have levels and all of that stuff.


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Post by WRA2 » Wed Aug 29, 2007 5:03 pm

Drag_Racer408a wrote: Also with a portable air compressor they sort of give a "Limit" on what pressures you can use. It prevents people who don't know what they are going with compressed gasses not get hurt.

And it would be too easy to just use a SCUBA tank, out hook it up and pressurize the rocket within 30 seconds and go.
This is one of the reasons for the compressor rule. Imagine a newbie competitor that tries to duplicate the Anti-Gravity effort by borrowing a nitrogen tank and connecting a garden hose or workshop air line to pressurize their rocket to similar pressure.
rockets42 wrote: what about scuba tanks? They are certified, you need to be licensed to get one refilled, they will only refill it with breathable air from the atmosphere using a compressor. There is nothing poisonous in it, and does not pollute the environment. Its just a convenient way of storing air.

If a compressor has any form air storage cylinder isn't that the same thing?

In terms of concerns for CO2 being released into the atmosphere that is true that we shouldn't do it. But doesn't running a compressor just produce CO2 at the power station?
The problem with a SCUBA tank is that how do you get enough pressure to launch a rocket with all of the proper SCUBA safety equipment (such as regulators) in place. It seems to me that with all these in place you would not get enough pressure to even launch. Removing these devices probably violates that license you have to get the tank filled.

There are cleaner forms of electric power (such as solar, wind or hydro-electric) which do not produce CO2.

One purpose of the compressor rule is to keep the playing field level for competing teams of various means.

Many of the rules have cost effectiveness in their design as much as safety. We have a rule of no metal on the pressure vessel. This is for safety as well as to insure some wealthy team does not machine a rocket from billet aluminum and squash all the hobby competitors. Our weight limit insures that nobody with a million dollars creates a 60 foot tall carbon fiber rocket and stinks up the show. The same is true for tanks. Tanks are expensive and filling them is expensive and we don't want to see some wealthy scuba diver come in and spoil the contest. Furthermore, competitors who live far from the ocean or in cold climate areas may not have easy access to scuba tanks or places to fill them, so we ruled them out in the interest of fairness.

If we allowed tanks in the competitions, it would make it a lot easier for a team with experience to run away with the lead. Imagine where USWR would be if we let them use tanks, or let them take off the heavy camera, or let them build any size rocket they wanted. We're trying to keep the competition close here by carefully limiting what can and cannot be done.


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Post by Drag_Racer408a » Wed Aug 29, 2007 8:55 pm

I have looked into paintball compressors before and they aren't cheap. Like a couple grand for a used one on ebay.

And it would be hard for me to get a SCUBA tank because i live in a cold climate type area where people really don't go scuba diving.

Also i got my compressor that puts out 250 PSI for like $25 from a local store. They are cheap and easy to use. Rather than having a whole bunch of regulators and stuff like on a Scuba tank.

If you are wanting to level the playing field shouldn't the rules state a maximum pressure regardless of the source of air?
The WRA2 requires the use of atmoshperic gas to be used as a level plaing feild. Different gases have different combustion ratios. There is no way to tell what is in the tank wether it is CO2 or Nitrogen.

why isn't there an upper pressure limit in the rules?
I think there isn't a upper pressure limit is first of all nobody could know if a team exceded the pressure on there record attempts. No officials are required for a record attempt.


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Post by Tim Chen » Sun Sep 02, 2007 12:33 am

I'm quite sure that compressors don't need to be periodically tested and certified. Just to get the topic back on track.


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Re: Compressor Certification

Post by bambambam » Mon Aug 24, 2009 3:31 pm

Wait, I'm gathering from this thread that compressors can be pretty dangerous. Are their any horror stories anyone knows about?



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Re: Compressor Certification

Post by WRA2 » Mon Aug 24, 2009 7:37 pm

bambambam wrote:Wait, I'm gathering from this thread that compressors can be pretty dangerous. Are their any horror stories anyone knows about?


All pressure sources are dangerous if the proper delivery systems are not used (pipes, hoses, valves). Compressors are safer then bottled air as pressurized gas does not need to be transported to the launch site.

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Re: Compressor Certification

Post by nonickname » Sun Aug 30, 2009 4:31 am

some other more highly compressable gas like CO2
Not exactly correct. CO2 liquefies in the area of 700-800 psi dependent on the temperature. Few water rockets (as-in-the-kind-made-from-plastic-bottles) will use anywhere near this pressure. In fact using, a gas like CO2 at an identical pressure will leave the competitor at a disadvantage to one using air (nitrogen and oxygen) due to the lower particle speed and specific impulse. Not noticeable without accurate measuring equipment, but not a disadvantage you'd seek to have.

CO2 also cools rapidly as it changes state from a liquid to gas, meaning your plastic will not fare as well.

If one were to seek ideal performance, they would use hydrogen (highest particle speed and SI). Though it's a difference of several feet in an un-optimized setup.

If every safety concern was taken care of I hardly see any reasons not to use regulated nitrogen, HPA, CO2, helium or whatever.



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