Launcher, version 2

Now my quest is on its way and i'm capable of launching water rockets at higher pressures. With these pressures i stumbled over some limitations from my cable tie / O-ring seal / tri-pod launcher. The drawbacks are mostly related to the O-ring seal.

Drawbacks
- O-ring seal into bottle neck has low margin for tolerance,
- O-ring compression is 0.6 mm or less, bottleneck variation is over 0.3 mm (practical measured figure).
- Construction of good O-ring seal requires precise dimensions / machining.
- Under high pressures O-ring wear, caused by friction during launch, is remarkable high, at 8 bar or higher the O-ring has to renewed after every 10 to 15 launches.
- At higher pressures the tie-wraps are stretched under the pulling force of the rocket (~ 400N @ 10 bar), rocket pulls itself out of O-ring area if used with less than 6 tie-wraps in my launcher configuration.
- Leakage is assured if rocket is not perfectly aligned with axis of launcher or forces (wind) act on rocket before launch.
So I was wondering if this could be improved?:

Wishlist:
1- Less susceptible for tolerances
2- Capable of withstanding higher pressures (>10 bar)
3- Better seal for not perfect aligned rockets.
4- Less wear.

While working on the garden hose based second stage release I came up with an idea to replace the O-ring seal with a piece of garden hose. This looks to work out perfectly after the first launches, the garden hose seal scores on the top three wishes. The less wear wish has to be proven in practice, now with to few launches done this way it still to early to tell.
Lets see how the construction looks and what working principle is.

First some pictures of the construction.
The copper pipe is the base of the construction. Three hose clamps hold the tie wraps in position. On the copper tube a bush is soldered (this is the lump in the hose). The garden hose is pushed over this bush and is fixed and sealed for the high pressures with some wire, i used copper wire for this. The garden hose extends over the copper pipe (smaller diameter) so the bottle neck is able to slip over the garden hose until it reaches the part of the hose where the bush is. Final, but a very important detail, not visible in the pictures, is a little hole in the copper pipe just to the right from the bush, where the hose has less diameter. This hole ensures that the pressure under the hose is the same as in the bottle. This to make sure that the hose is not squeezed on to the copper pipe by the pressure but will expand.








And here a picture with the PVC slide away sleeve mounted, sleeve holds the tie wraps in position and the bottle in lock before launch.















Well I hear you think, nice pictures but how does it work???.
Let me tell you it works fine!! (just kidding)


The green parts in the picture is the bottleneck.
The pressure (coming in via the hole) lets the hose expand under the bottle neck opening. Because the pressure on the outside of this part of the hose is only atmospheric. The hose forms a tight seal with the rim of the bottle neck. If the position of the bottle is changing a bit, the hose will adapt, the construction is less susceptible for tolerances and mis alignment (wish shortlist 1 and 3). Because only a small part of the hose is under pressure it will withstand high pressures. (wish 2).
The wish on wear has still to be proven, don't know yet how the hose will hold after lots of launches.
For an explanation on the rest of the tripod launcher please see the description of the first version of the launcher in the construction overview.