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The purpose of this tutorial is to build a simple remotely operated pressure release valve out of common materials requiring no special tools.

Background

An abort valve is a very important safety feature of a launcher. On occasions you will encounter a situation where an already pressurised rocket needs to be prevented from leaving the pad and pressure in the rocket needs to be released. Some reasons for aborting a launch include:

  • The recovery system malfunctions or accidentally deploys while the rocket is still on the pad.
  • The range may become unsafe such as when people, vehicles or animals enter the range.
  • A slow leak may develop that might lead to a catastrophic failure if pressure is not released quickly.

While a pressure release valve could be located close to the air source, a problem exists if the launcher needs to use a non-return valve (check valve) to keep the water from flowing back into the air line. In this case the non-return valve should be located as close to the rocket as possible. In order to release pressure from the rocket the pressure release valve needs to be located on the rocket side of the non-return valve. Having a manual pressure release valve next to the rocket means a person would need to operate it while standing next to the pressurised rocket. A remotely operated valve is required for safety.

You may want to prevent water from going back down the air line for two main reasons:

  • Keep as much of the water in the rocket as possible.
  • The water may damage your pump if it is designed only for air.

If your launcher uses a launch tube that only allows air into the rocket above the water line you may not need the non-return valve, however, it is still a good idea to have one in order to prevent water escaping down the launch tube and into the air hose while loading the rocket onto the pad. And when the rocket takes off water is forced down the tube.

It should be possible to attach this mechanism to the air line of most existing launchers if they're not already fitted with non-return valves. In the procedure below we integrate a simple non-return valve into the pressure release valve.

For more water rocket construction tutorials please visit:

http://www.AirCommandRockets.com

Step 1: Materials Needed

  • 2 x Gardena quick connectors
  • Gardena extension adaptor
  • Hose clamp
  • Epoxy glue
  • Sewing pin with a round head
  • Nylon String

Step 2: Tools Needed


  • Scissors
  • Drill
  • Screwdriver
  • Sandpaper
  • Pliers
  • Blu-Tack / plasticine / modelling clay

Step 3: Procedure

If you are going to fit this mechanism to a launcher that does not require a non-return valve then you can skip steps 3 - 9.

We start with an integrated non-return valve.

Procedure

Sand the internal hole of the Gardena quick connector.

Step 4:

Put a piece of Blu-Tack, plasticine or modelling clay on the workbench and stand the Gardena connector on it's end (orange collar pointing up) so that the Blu-Tack blocks the central hole. You may want to make a protective cylinder from a piece of paper so that you don't get glue on the inside walls near the top of the coupling.

Step 5:

Mix up some epoxy and carefully pour it through the open end. Pour enough epoxy in so that it is about 1cm deep.

Step 6:

Let the epoxy fully cure for at least 24 hours. It is better to use the longer cure but stronger epoxy than the 5 minute stuff.

Step 7:

When the epoxy has cured, drill a small hole through the center of the epoxy. The hole should be smaller than the head of the pin. Usually about 1.5 - 2mm is good.

Step 8:

Insert the pin so that the head is on the inside of the coupling. With the sharp end pointing out of the hole.

Step 9:

Cut the sharp point off and bend the end of the pin 90 degrees. The bent section should be about 3 mm and there needs to be about 5mm movement of the pin. This is the non-return valve.

Step 10: Pressure Release Valve

For illustration we show the launch abort valve fitted to a simple Gardena launcher.

Step 11:

Here we cut the garden hose air line where we want to fit the abort valve.

Step 12:

Insert the two hoses into the respective couplings making sure that the one with the non-return valve is closer to the air source. Tighten the coupling nuts to secure the hoses. Snap the extension adaptor into the hoses to check to make sure everything fits.

Step 13:

Put a hose clamp around the coupling with the non-return valve and pinch two ends of loop made from a short length of string under it.

Tie a string around the hose near the base of the coupling and run it to the other hose near the base of the other coupling and tie it off. Do this three or four times around the couplings. Make sure that there is enough slack in the lines to allow about 2 cm of movement.

Step 14:

The pressure release valve is now complete. You will want to attach the hose near the rocket to the launcher so that it does not move when you pull on the abort string.

Connect a long string to the short loop on the valve. Make the string as long as your launch string. It is a good idea to make it a different colour so that you don't accidentally pull the wrong one.



NOTES:

1. If you use an air hose that is a different diameter to the garden hose used in this example, you can use a short lengths of garden hose connected to the couplings, and make hose adapters for your specific air hose. There are many adaptors available on-line or from your local hardware store. Here some examples:

http://www.fittingsandadapters.com/brasshosebarbs.html
http://www.justoffbase.co.uk/Tool-Shop/Air-Hose-Connectors

You can also easily insert a inner tube (Schrader) valve into the end of the hose and use a small hose clamp to secure it in place. Be aware that these don't work as non-return valves when the air hose is connected to them.
2. You should be able to use brass Gardena couplings or similar quick connect fittings if you wish to use higher pressures, but make sure that any connected hoses are also rated for the appropriate pressures.
3. To reset the valve simply click the couplings back together.
4. The simple 'pin' non-return valve is less than ideal, but for the most part it should seal well.
5. You may find a Gardena quick connector that already has a non-return valve built in. These are unsuitable as the valve only operates when nothing is snapped into the connector.

References

For more water rocket construction tutorials please visit:

http://www.AirCommandRockets.com
this doesnt seem like it would work with a multi stage rocket, or atlest not on the uper stages. any ideas to solve that?
Correct, this would only let the pressure out on the first stage. One way to solve an upper stage pressure release (how we do it anyway) is that the second stage has a small loop of wire tied near the nozzle into which a carabina attached to the launcher with a string can be clipped on. The second stage is then released as normal, but the string prevents the second stage from flying away. The only drawback with this method is that you have to approach a pressurised rocket.
&nbsp;You could just run a piece of pipe from a T connector to a valve near you, if you then need to abort the launch, just open the valve. The only disadvantage is that you loose water :)<br />
The problem is that if you are using a non-return valve to prevent water from leaking out of your rocket and into the air line the non-return valve needs to be as close to the rocket as possible. The abort valve needs to be on the rocket side of the non-return valve. Running a hose back to your position for the abort valve would mean that the whole hose could fill up with water from the rocket before launch. <br />
where do you by in the US gardena quick connectors. could i buy then at home depot or menards
Pretty much any place that will sell you a garden hose. Home Depot definitely, even your local supermarket might.
Very nice! You have a cool rocket setup, but I think I still prefer using PVC and a ball valve. Is there a reason you are using hose in particular?
The launcher above uses a garden hose purely for simplicity. Almost everyone has one in their backyard and can easily make a launcher from one. PVC is very good too but you need to take care not to over-pressurize it. A bursting hose is slightly less dangerous than bursting PVC. Do you operate your ball valve close to the pressurised rocket?
Well, you can tie a string to the valve and pull it to twist it. How do you get the hose mechanism to work well on the rocket? How do you keep the pressure from blowing it off and how do you release? Just pull with a cord? The mechanism I had on my old bottle rocket used PVC and O rings, along with a Clark Cable release mech, but now that it is gone I need a new mech, preferably cheap. Is there somewhere I can go to make that mech?
The plastic Gardena hose quick connector can hold quite a bit of pressure. In tests we've had it hold over 220psi without problems. I'm not sure about cheaper plastic ones though. The brass ones can handle more pressure still quite comfortably. You are correct, we just have a cord attached to the collar of the connector and you pull on that to release it. If you want to make a Gardena launcher, just search on Google for "Gardena water rocket launcher" and you should find quite a few references on how people build them. You can make the launcher for less than $10. Remember that your rockets will have slower but longer take-offs due to the restricted nozzles.
Aye aye! Would it be possible to add... hmm... nevermind. I thought it might be possible to make the nozzle opening larger
There are 15mm Gardena nozzles available. We use these on some of our rockets. You need the corresponding 15mm gardena coupling for the launcher though.
WoW!! Thanks for another excellent write-up! <br/>I would have to say, an abort valve is almost as important as the actual rockets structual integrity.<br/><br/>I build abort valves on every launcher setup, especially ones which do not have an active pressure gauge built into the launcher.<br/><br/>Many times I have had a loaded rocket, which would not launch. Generally when it tips slightly and the quick connect gets jammed. Without an active gauge, you can not tell whether the air has leaked and it is not loaded, or whether it is jammed...<br/><br/>I would throw rocks at it before moving in to touch the rocket laucher....<br/><br/><strong>Abort valves are our given grace, in a very dangerous past time...</strong><br/>They are a necessity and so is this I'ble.<strong></strong><br/><br/>You should post that u-tube vid of the teacher gettin' smacked in the face, or was it a near miss? I think it was a near miss... <br/><br/>Anyway you don't want to cop a rocket in the face, not nice.<br/>

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