Hello and welcome to this video! If you
are interested in building advanced water rockets
there is one component of the rocket
that is critical to its success: the
pressure vessel. In this tutorial we want
to show you how to build a very strong
and reliable one. Before you can get
started with the construction you should
definitely have an idea of how your
water rocket will look like. We recommend you to watch our video that explains the
different methods of construction and
what's important when it comes to
building a water rocket. Regardless which
methods of construction you go for, the
principle of building the pressure vessel is always the same:
Multiple plastic bottle sections are
combined together. However, not all bottle types
can be used for water rocketry.
The bottles should be as strong as
possible and should have a long cylindrical section. In this video we are
using bottles from Apollinaris, but these
bottles are maybe not available to you
depending on your Location. There are
many ways to combine the bottle sections.
The most popular one is to cut off some
parts and glue them together with
polyurethane based adhesive. You can also
put together multiple pressure vessels
by using specific connectors. In this
video we are going to build a pressure
vessel with six joints. However, the
method of construction and the number of
joints can be adjusted to your liking.
But first of all you have to prepare the
bottles. Cut off both the lower and the
upper sections but leave two bottles out
and remove only the lower section from
them.
When cutting off the sections it is
useful to mark the areas with a marker
pen and a piece of paper. You can also
use a jig consisting of a drilling
machine and a cutter. It is very
important to ensure an even cutting edge.
To combine the bottles together you have
to shrink them on one side. The bottle
type we use in this video is a little
bit conical and so we choose the
slightly smaller size. But before you are
ready to shrink the bottle you have to
turn it on a hot iron. To shrink it just
put the bottle sections in about 2.5
centimeters or one inch deep hot water.
Depending on the water temperature the
process will only take one or two
seconds. If you wait too long the bottle
will bring too much. Always keep in mind
that it is important that you shouldn't
be able to put the sections together too
easily. If this is the case you should
replace the sections before continuing
with the next step. Before you glue the
bottle sections together you have to
sand the shrunken areas on the outside
and the other bottle ends on the inside.
Furthermore, you should also clean them.
We recommend polyurethane based adhesive
to stick the bottles together. But watch
out: Not every adhesive is suitable for
building water rockets. For example, we
have good experience with
PL Premium. Other adhesives like
Sikaflex 11 FC are very good to seal
something -  but not so much for holding
together a rocket chamber. Nevertheless
you should choose this adhesive if you
plan to reinforce your rocket with
fiberglass or carbon fiber because the
reinforcements will hold the vessel together
while the adhesive seals the joints.
The pressure at launch can be increased
up to 18 bars or 260 psi. We recommend
using a jig which holds the chamber in
place. It is very important to wear gloves
because you should not comein contact with the adhesive. We also suggest
opening all the Windows. Now you can
start applying adhesive on the sanded
bottle areas. Be very careful when
sticking the sections together and do not
twist the sections while doing so. You
can reuse some of the excess glue for
the next section. If you have joined all
bottle sections together rotate the
pressure vessel to make sure it is not
crooked. After that, wait at least two or
three days before you continue. In case
you don't plan to reinforce your rocket
you can now proceed with the pressure
test. We explain how that works later in
this video. But if you plan to reinforce
your rocket we still have a lot of work
to do: The whole chamber has to be sanded. To start with the reinforcements of your
pressure vessel you have to cut the
fiberglass to size. We recommend using
two layers of fiberglass. That means that
the textile has to be wrapped two times
around the chamber. Thus, the dimensions
of the required fiberglass are: length of
the chamber to 6.4 bottle diameters. 
Be very careful when cutting the
fiberglass because you do not want to
pull out fibers from the cloth. At both
ends of the fiberglass we cut in little
stripes so that the reinforcement can
fit tightly at the ends of the pressure
vessel. To reinforce it, you once again
need a jig to hold the vessel in place.
The resin is mixed in the ratio given on
the packaging. Keep in mind that you
should wear gloves and open the Windows.
After that, the resin can be applied to
the pressure vessel using a roller. In
case the bottle type you use has any
patterns or notches you can use single
fibers to fill them and make the surface
of the chamber more even. Now you can
start wrapping the fiberglass on the
chamber. For that, lay the cloth very
carefully on the pressure vessel. Use the
roller to press the applied resin on the
chamber through the fiber glass until it's
see-through. Every now and then you may
have to add some resin. However, keep in
mind that you shouldn't use too much.
Be very careful at the ends of the pressure
vessel. After completion, we suggest
wrapping a single fiber around the
thinnest part of the bottleneck. Wait at
least a few days before continuing with
the pressure test, we even recommend
waiting a week. But that doesn't mean
that you can't do anything in this time.
You can remove protruding fibers and you
can send, if necessary, parts of the
vessel using wet and dry sandpaper. Now
that your pressure vessel is nearly
finished you just have to test it before
you can use it for your water rocket.
For that fill the chamber almost completely
with water and put it behind the barrier.
You can use your launchpad to build up
pressure or you can build a dedicated
system for it. A reinforced pressure
vessel can hold up to 18 bars or 260 psi,
most pressure vessels without
reinforcements can hold about half that.
You should definitely test the chamber
to a higher pressure than you plan to
use it on your rocket. If your chamber has
passed the test it is ready to be used
in your rocket. We hope you enjoyed this
video and that we were able to help you.
If you want to learn more about the
other water rocket components, check out our
YouTube channel and our Website. We'll
see you next time.
Your Raketfued-team
