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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.

250 psi compressors review

Discussion about Compressors, hose, pipes, fittings, launchers, release mechanisms, and launch tubes.
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RaZias
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250 psi compressors review

Post by RaZias » Wed Apr 28, 2010 2:30 pm

I made burst testing with small compressors and I found these conclusions:

---------- 250 psi 12V compressor (Bought in the LIDL markets. Made in Germany ?)


It couldn´t pass from 180 psi with a 2 L bottle (it just stopped there)

But it achived 250 psi by pressurizing a tube with a small volume.
250 psi box.jpg
under 250 psi box.jpg


---- 300 psi 12V compressor ( made in china ? Bought in a market)

It achived 230 psi with a 2 L bottle...then it started losing air so now it´s a useless compressor.
300 psi.jpg
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Re: 250 psi compressors review

Post by joelo » Fri Apr 30, 2010 8:27 pm

Hi RaZias!
Can you post a picture of the air compressor (LIDL) that sees the air connectors?
Today I made a test with my (12v LIDL air compressor), with an 1 L Coke Bottle and it was until 120 psi, since then the compressor loosing air and I can't exceed 80 psi...
what it could be?
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Re: 250 psi compressors review

Post by RaZias » Sat May 01, 2010 7:49 am

Aqui estão as fotos.

A primeira é da ligação do compressor. Tu mudas-te esta ligação e talvez seja lá a fuga de ar.

É melhor comprar compressores da marca COIDO pela net (também se vendem no LIDL).
São compressores em forma de caixa rasa (como mostrei na foto dentro duma caixa).

Tenho um compressor igual ao teu e após de levar a 230 psi também passou a ter fugas de ar...

Agoro so uso da marca COIDO (se quiseres um se calhar tens de comprar na net dum site romeno acho eu).
ligação compressor.jpg
Esta foto demonstra a ligação do lançador ao compressor.
Se não conseguires arranjar a ponteira que está metida no tubo vermelho sempre podes colar uma valvula de bicicleta com araldite a um conector de pressão como tenho na foto.

Tens de retirar a borracha preta da valvula até se ver o metal.
MAS DEIXA UM PEQUENO DISCO DE BORRACHA na extremidade da valvula para evitar que o araldite se entranhe no mecanismo de vedação do conector de pressão.
(se não perceberes avisa).

Porque quis mudar da ponteira para a valvula ? Bem assim posso encher ate 10 bar com bomba manual e depois com o compressor ate 250 psi (aquecendo assim menos o compressor).

A ponteira deixa sair o ar quando mudo de bomba manual para compressor, a valvula evita isso.
ligações.jpg
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Re: 250 psi compressors review

Post by joelo » Sat May 01, 2010 6:56 pm

Olá! Obrigado pela resposta! Não sabia que se podia comunicar em PT... O meu inglês também é fraquinho...
Tenho quase a certeza que a perda de pressão é no compressor como o vídeo o demonstra... Uma pergunta, para o outro compressor que referis-te que perde pressão também tinhas as mesmas ligações que descreves-te no post anterior?

[youtube][/youtube]



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Re: 250 psi compressors review

Post by U.S. Water Rockets1 » Sat May 01, 2010 9:37 pm

Interesting topic. You guys should post your discoveries and recommendations in a summary when you have made any conclusions!


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Re: 250 psi compressors review

Post by RaZias » Sun May 02, 2010 3:23 pm

Hi, Joelo.

I didn´t cutted the black tube of the compressor has you did.

Anyway I made tests with 2 different compressors.
The flat 250 psi compressor of the mark COIDO doesn´t lose air.
The 300psi compressor that is just like yours started losing air when I achived 230 psi.

So loss of air it´s not from the connections or from the bottle but is from the cheap compressor :(

Anyway here are the connections:
connectors 1.jpg
connectors 2.jpg
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Re: 250 psi compressors review

Post by RaZias » Sun May 02, 2010 4:26 pm

You should open the compressor. The black exterior of the compressor are made of 2 half parts.

So you lay the compressor lateraly and remove one of the half exterior part.

Then put the compressor working and stop it at any pressure. You must place small drops of water with a small brush ("pincel" in portuguese) in some structures of the compressor to see if it makes air bubles.

The structure of the compressor is easy, it´s a piston chamber connected to a electrical motor by 2 gears.

I don´t know if the loose of the air is from the "piston chamber" or from the "black tube".

If you want to buy another bomb you should search for "12v compressors" in google.

See this one:

http://www.theultimatefinish.co.uk/ring ... ng-dot-com


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Re: 250 psi compressors review

Post by joelo » Mon May 03, 2010 7:51 pm

I think that already I found the problem:

I think that the responsability is the "good" chinese isolation glue...
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Re: 250 psi compressors review

Post by RaZias » Tue May 04, 2010 6:00 am

I have found the same structure in the photos of my compressor.
I will test in Friday if is the problem is also there.

If you fix the problem tell me what you did please. Will you use "epoxy araldite" ?


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Re: 250 psi compressors review

Post by RaZias » Fri May 07, 2010 1:21 pm

The black structure you showed in your photo doesn´t exist in the top of my piston chamber.

Anyway I didn´t identified the cause of the loss of air of my compressor...I couldn´t ear where the air was coming out...

Anyway I leave here a photo of an air selant plastic around the piston head.

It´s damaged so I think it´s why it loses air...I guess.
piston damaged.jpg
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Re: 250 psi compressors review

Post by joelo » Fri May 07, 2010 7:09 pm

Hi! First i try to use Teflon on the screw, but have an irregular surface, because of that don't work...Three days after putting araldite on the black top screw i made a test... lose pressure again but this time slowly... detected the cause of that (in the pressure meter connection) i put teflon on that screw and i made an ring seal with an air chamber of a bicycle tire... in a quick test i saw that doesnt lose pressure again... tomorrow i will test again with a coke bottle...

P.S Sorry my bad bad english... i hope that pictures helps:
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Re: 250 psi compressors review

Post by U.S. Water Rockets » Sun May 09, 2010 12:43 am

You guys may want to look for a safety system built into the compressor. We did a bunch of testing a long time ago and we had some compressors that had a safety pressure release that would fail below the rated pressure. The safety plug would fail and was a "one shot" device. Once it went off, it would be useless. We plugged the safety to continue using the compressor at higher pressure.



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Re: 250 psi compressors review

Post by RaZias » Sat May 15, 2010 4:37 pm

U.S. Water Rockets wrote:You guys may want to look for a safety system built into the compressor. We did a bunch of testing a long time ago and we had some compressors that had a safety pressure release that would fail below the rated pressure. The safety plug would fail and was a "one shot" device. Once it went off, it would be useless. We plugged the safety to continue using the compressor at higher pressure.
USWR: Could you show us a photo of the safety pressure realese ?

Joelo: I putted glue in 2 places (over the screw and over the manometer connection) it still loses air.
Anyway I found one solution, is to put a tap ( " torneira " in portuguese) in the connection system,
so when you achive the desired pressure you close the tap, that way only the compressor will loose air and not the launcher.

This is a picture of what I was working on, but I shouldn´t have putted a bike valve there because it´s looses pressure at high pressures...it´s better to make as the modification you did in the compressor, I mean in the end of the black tube of the compressor.

Here is the mambo-jambo stuff I was working on, soon I will remove the bike valve for something suitable.
tap with connections.jpg
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Re: 250 psi compressors review

Post by U.S. Water Rockets1 » Sat May 15, 2010 9:59 pm

RaZias wrote: USWR: Could you show us a photo of the safety pressure realese ?
Unfortunately, we did our testing on the inexpensive compressors in 1993 and 1994, meaning the pumps have long since been discarded. We never did an extensively documented tear-down of the pumps so we only have some collective memories of the designs.
  • * One design had a machined area of the cylinder itself where the metal was cut very thin and was designed as a burst disk.
    * A second design was made from a hollow tube which was threaded into a "tee" internally. The hollow tube had a plastic insert pressed into it that blew out under pressure.
    * A third design was the use of a steel pipe which was pressed into the top of the cylinder. The steel tube connected the cylinder to the hose and gauge and was apparently designed to "pop off" under pressure.
There's probably many other ways to make these pumps safe. In the U.S. everything is regulated to prevent people from hurting themselves either by laws or by companies avoiding lawsuits. Maybe other areas of the world they have more robust designs?


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Re: 250 psi compressors review

Post by RaZias » Sun May 23, 2010 2:48 pm

I made a test with the 2 compressors I posted in the beggining and these are the conclusions:

Both went only at 180 psi with a 2L bottle :(

The one that achived 230 psi had in fact a falty manometer, so instead of reading 180 psi it gave 230 psi.
That falty one is the cheapest and made in china.

Soon I will try to connect one of the 12v compressors to a 24v transformer.

I really want to get 300 psi :evil:


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