New launch tube sealing method

Discussion about Compressors, hose, pipes, fittings, launchers, release mechanisms, and launch tubes.
SaskAlex
WRA2 Member
WRA2 Member
Posts: 238
Joined: Tue Apr 07, 2009 2:36 pm

New launch tube sealing method

Post by SaskAlex »

A while ago I thought of a new way to seal bottle necks to launch tubes. It's kind of like a compression fitting. The advantage is that you do not need any o-ring built into your launch tubes. Here's how it works:

Start by drilling a large hole in a bottle cap. Put the cap on a bottle neck and file it out to the full inside diameter of the bottle neck. It should look like the cap below.
1.jpg
1.jpg (45.36 KiB) Viewed 182 times
Now place that bottle cap over your launch tube. Place an o-ring and finally your rocket over the launch tube.
2.jpg
2.jpg (24.1 KiB) Viewed 182 times
Screw the cap onto the bottle and you're done! The cap pushes the o-ring against the bottle and the launch tube.
3.jpg
3.jpg (24.7 KiB) Viewed 182 times
Conveniently, if you pull the bottle off of the launch tube the o-ring stays in place due to friction. Next time, just slide the bottle on the launch tube and it's ready to go.
4.jpg
4.jpg (36.52 KiB) Viewed 182 times
Due to a lack of suitable rockets or launchers, I have only tested this up to about 110 psi so far. However, I think it should hold high pressures because if you tighten the cap quite firmly and don't have any lube or water on the o-ring or launch tube, then the bottle is hard to move up and down the launch tube. This must mean the o-ring is being pushed rather firmly into the launch tube. It's not quite as nice as having a permanent o-ring in your launch tubes, but it has several advantages. First of all, one cap and o-ring can work for all of your launchers/launch tubes and all of your rockets. Secondly, the seal can be made at any position on the launch tube. If someone makes a release mechanism that can slide up and down on a launch tube (and be locked in place, of course) then you would have a launcher with an easily adjustable launch tube.

Alex
RebelRockets
Advanced Member
Advanced Member
Posts: 54
Joined: Tue Sep 08, 2009 9:51 pm

Re: New launch tube sealing method

Post by RebelRockets »

Hi Alex,

I can see how this idea could be adapted to use a reduced nozzle insert inside the bottle neck along with a smaller diameter launch tube. You could possibly change out several different nozzle sizes and matching tubes.

With a more conventional o-ring mount on the launch tube, the o-ring rubs against only about a half inch of the bottle neck per launch. With this method it would rub against maybe 9 inches or more of the launch tube. Would that create more wear on the o-ring? Would that longer contact reduce the speed at launch? It would maintain the seal until the end of the tube but does it reach the same speed as a looser fitting tube?

Dennis
SaskAlex
WRA2 Member
WRA2 Member
Posts: 238
Joined: Tue Apr 07, 2009 2:36 pm

Re: New launch tube sealing method

Post by SaskAlex »

Yes, I imagine the o-rings would wear out much faster with this method. At least they are easy to change.

As for the force on the launch tube, I don't think it's a big deal. With a wet or lubricated launch tube the bottle can moved along the launch tube with what feels like just a few pounds of force. I've had certain launch tube/bottle neck combinations that had just as much friction. The friction is pretty negligible compared to the 100 pounds or so of force between the bottle and launch tube.
User avatar
RaZias
WRA2 Member
WRA2 Member
Posts: 751
Joined: Mon Jul 14, 2008 3:16 pm

Re: New launch tube sealing method

Post by RaZias »

There are Teflon Sprays for bike chains, that would reduce the wear-out for the o-ring...but I think that 10 o-rings are more cheaper than a Teflon Spray.

There is also Teflon Tape, wich continues to be more expensive than 10 o-rings...

Anyway, nice idea. I will try it soon.
Research and Development is the soul of WR
SaskAlex
WRA2 Member
WRA2 Member
Posts: 238
Joined: Tue Apr 07, 2009 2:36 pm

Re: New launch tube sealing method

Post by SaskAlex »

I've been playing around with these a bit more in the shop. There is actually quite a bit of friction if used on a metal launch tube. On PVC, it's pretty decent though. Personally, I don't think I'll use these seals to seal my rocket to the launch tube, but they are handy for other things. For example, I already made a pneumatic plunger with them for one of my launchers.
User avatar
rockets-in-brighton
Senior Member
Senior Member
Posts: 431
Joined: Fri Jun 20, 2008 12:33 pm

Re: New launch tube sealing method

Post by rockets-in-brighton »

This was the method I tried for my first launcher, because as you say it was easier to prepare caps with seals that to fit an O ring to the launcher. It was unsuccessful in practice and I abandoned it almost immediately. Looking back, I think the problem was that I have always used a launcher with a long launch tube. Add the high friction of this kind of fitting and you get sluggish - or even completely failed - launches. It might still have some merit if you use a stubby launch tube, just long enough to fit inside the bottle spout, and maybe with external launch guides to assist.
Cheers
Steve
Rockets-in-Brighton
WEB: http://groups.google.co.uk/group/rockets-in-brighton
SaskAlex
WRA2 Member
WRA2 Member
Posts: 238
Joined: Tue Apr 07, 2009 2:36 pm

Re: New launch tube sealing method

Post by SaskAlex »

rockets-in-brighton wrote:This was the method I tried for my first launcher, because as you say it was easier to prepare caps with seals that to fit an O ring to the launcher. It was unsuccessful in practice and I abandoned it almost immediately. Looking back, I think the problem was that I have always used a launcher with a long launch tube. Add the high friction of this kind of fitting and you get sluggish - or even completely failed - launches. It might still have some merit if you use a stubby launch tube, just long enough to fit inside the bottle spout, and maybe with external launch guides to assist.
Steve, I just read your post and it prompted some quick experimenting. I threw a bottle on one of my PVC launchers (sch. 40 white plumbing PVC) to see how much pressure it took to over come the static and dynamic friction. I tightened the cap up quite firmly, and it would start moving up the launch tube before my pump's guage even showed any pressure (well under 10 psi). So clearly the friction is pretty negligible. However, I also tried out an older launcher which uses grey plumbing PVC. I guess there is a difference in finish, because it took about 30 psi to overcome the dynamic friction, and that wasn't even with the cap snugged up too tight.
User avatar
U.S. Water Rockets1
WRA2 Member
WRA2 Member
Posts: 1778
Joined: Sat Feb 03, 2007 3:24 pm

Re: New launch tube sealing method

Post by U.S. Water Rockets1 »

SaskAlex wrote:
rockets-in-brighton wrote:This was the method I tried for my first launcher, because as you say it was easier to prepare caps with seals that to fit an O ring to the launcher. It was unsuccessful in practice and I abandoned it almost immediately. Looking back, I think the problem was that I have always used a launcher with a long launch tube. Add the high friction of this kind of fitting and you get sluggish - or even completely failed - launches. It might still have some merit if you use a stubby launch tube, just long enough to fit inside the bottle spout, and maybe with external launch guides to assist.
Steve, I just read your post and it prompted some quick experimenting. I threw a bottle on one of my PVC launchers (sch. 40 white plumbing PVC) to see how much pressure it took to over come the static and dynamic friction. I tightened the cap up quite firmly, and it would start moving up the launch tube before my pump's guage even showed any pressure (well under 10 psi). So clearly the friction is pretty negligible. However, I also tried out an older launcher which uses grey plumbing PVC. I guess there is a difference in finish, because it took about 30 psi to overcome the dynamic friction, and that wasn't even with the cap snugged up too tight.
You could try using teflon impregnated o-rings to reduce the friction even further. That should eliminate any problems with the rocket sticking. They are quite a bit more expensive, but it does save a lot of work embedding the o-ring into the launch tube.
Team U.S. Water Rockets
Visit USWaterRockets.com
Visit our Blog
Tune in to our YouTube Channel
Visit our Facebook page
Visit our Twitter Page
Opportunity is missed by most people because it is dressed in overalls and looks like work. --Thomas Edison