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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.


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Question on rules for pressure vessel

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Re: Question on rules for pressure vessel

Post by Water Rocket Expert » Fri Mar 07, 2014 11:08 am

The tube has an ID of 60mm and a 1.5mm wall thickness. It is 2.66m in length and weighs about 900g. GRP suggested to us that we only use the tube up to 6 bar. We are reinforcing the tube ourselves to meet our pressure requirements.[/quote]

If it was not intended for high pressure that sounds fine. WRA2 needs to give it the final say but if you are reinforcing it yourselves, then it seems fine. I'm surprised GRP says to use it only to 6 bars. I wonder how much USWR's pressure vessel weighed. This might sound off the wall, but in my opinion a tube of T-12 would be lighter than the tube your buying and it can already hold 6 bars also. You would probably do well to use than and then just reinforce it because there is no point in getting two pipes of the same strength and reinforcing the heavier one and using it. I could be missing something so let me know if this is right.

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Re: Question on rules for pressure vessel

Post by WRA2 » Fri Mar 07, 2014 6:09 pm

Ascension wrote:
The tube has an ID of 60mm and a 1.5mm wall thickness. It is 2.66m in length and weighs about 900g. GRP suggested to us that we only use the tube up to 6 bar. We are reinforcing the tube ourselves to meet our pressure requirements.
Since it is not a purpose built "pressure vessel" (as noted by the 6 Bar max recommended pressure), you may use it.

Be careful of the weight though, at 900 grams, you leave little room for additional reinforcement. Remember that the entire rocket in flight ready condition (dry weight) cannot exceed 1,500 grams. This includes the pressure vessel, end caps/nozzle, fins, payload bay, altimeter, camera, deployment mechanism, nosecone, batteries, and parachute. In other words, prep the rocket like you are going to fly it but don't fill with water and put it on a scale.

It has to weigh less than 1,500 grams.


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Re: Question on rules for pressure vessel

Post by U.S. Water Rockets1 » Sat Mar 08, 2014 11:12 pm

It is a good idea to make the electronics and recovery systems and all the other parts first and then weigh them. That way, you know how much weight you have to budget for the pressure vessel. You can always add or subtract the amount of reinforcement you use to adjust the eventual weight of the rocket. Then you adjust the launch pressure accordingly.


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