Cutting off the lower section

Jig consisting of a drilling machine and a cutter

Turning bottles on a hot iron

Applying carefully adhesive

Sticking the sections together

You can reuse some of the excess glue

Cutting fiberglass

Fill paterns and notches with single fibers

Press the applied resin through the fiberglass

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.

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   a   barrier . You   can   use   our   launch   pad   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 reinforcement   can   hold   about   half   that.   However, that   largely   depends   on   how   experienced   you   are and    how    conscientious    you    work.    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.

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 take    a    look    at    our    tutorial    that    explains    the different     methods     of     construction     and     what’s important    when    it    comes    to    building    a    water rocket.   Regardless   which   method   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    plastic    bottles    can    be    used    for water   rocketry.   The   bottles   should   be   as   strong   as possible     and     should     have     a     long     cylindrical section .   In   this   tutorial,   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   called Tornado Tubes . 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   from   the bottles,   but   leave   two   bottles   out   and   remove   only the lower section from them but not the neck.

When   cutting   off   the   sections,   it   is   useful   to   mark the   areas   with   a   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   bottle   sections,   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   side.   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 2.5cm   or   1   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 shrink   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   section   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    the bottle sections.

We   recommend   polyurethane   based   adhesive    to glue   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    11FC     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    reinforcement    will    hold    the vessel   together   while   the   adhesive   seals   the   joints   . Thus,   the   pressure   at   launch   can   be   increased   up to 17 bars or 250 psi. We     recommend     using     a     jig     which     holds     the chamber    in    place.    It    is    very    important    to    wear gloves ,   because   you   should   not   come   in   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    tutorial.    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   reinforcement   of   your   pressure vessel,   you   have   to   cut   the   fiber   glass   to   size.   We recommend   using   two   layers   of   fiber   glass.   That means   that   the   textile   has   to   be   wrapped   two   times around   the   chamber.   Thus,   the   dimensions   of   the required fiber glass are: Length of the chamber x 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   fiber   glass,   we   cut   in   little stripes   so   that   the   reinforcement   can   fit   tightly   at the ends of the pressure vessel. To   reinforce   your   pressure   vessel,   you   once   again need   a   jig   to   hold   the   vessel   in   place.   We   simply   use a   PVC   pipe   for   that.   Don’t   forget   to   mask   the   bottle thread   with   a   little   bit   of   tape.   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   to the   chamber.    For   that,   lay   the   cloth   very   carefully on   the   vessel.   Use   the   roller   to   press   the   applied resin   on   the   chamber   trough   the   fiberglass   until   it’s see-trough.      Every   now   and   then   you   may   have   to add    some    resin,    especially    at    the    second    layer. However,   keep   in   mind   that   you   shouldn’t   use   too much   resin   because   that   increases   the   weight   of your   rocket.   Be   very   thorough   at   the   ends   of   the pressure    vessels.    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    sand,    if necessary,   parts   of   the   vessel   using   wet   and   dry sandpaper .

PART 1: PRESSURE VESSELS

PART 2: REINFORCEMENT OF THE CHAMBER (OPTIONAL)

PART 3: PRESSURE TEST

Latest update: 6.2.1.2|2nd April 2020

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