Deck Fill Protection Device
Manufactured by Marsh Marine...Tank Cleaning Professionals         “Our experience is your protection since 1966”
Diesel Fuel...Continued: A ir   will   enter   a   tank   only   when   its   fuel   level   diminishes,   i.e.   you   are   using   or   draining   fuel,   or   the   fuel   is contracting   due   to   cooling.      Since   it   is   heating   up,   expanding,   air   will   be   vented   out,   not   into   the   tank.      Precise studies   have   shown   that   even   with   the   air   entering   a   tank   that   is   100%   saturated,   the   amount   of   condensation   it might   deposit   on   the   tank   walls,   if   the   tank   were   indeed   cooler   than   the   outside   air,   is   too   small   to   ever   become a problem. There simply is not enough volume exchange to make much difference.  If you are finding water in your tanks or fuel bowls, believe me it isn’t from condensation.  It got there from bad fuel you took aboard, a leaking fuel cap, a leaking fuel level sender, or an improperly installed fuel vent.  Never take for granted that fuel received from a marina is clean.  We do fuel maintenance for several marina storage tanks and always find water.  Ask to see the filter system your marina uses and when it was last changed.  W hen   was   the   last   time   you   inspected   the   “O”   ring   gasket   on   your   deck   fuel   fill   cap?      Does   it   even   have   one? Ever   clean   or   grease   it?      This   is   a   common   leak   point.      Decks   get   water   on   them   and   if   the   cap   leaks,   you   get water   in   your   fuel.      Check   the   cap   and   clean   the   seal.      Replace   the   ring   if   it   is   worn   or   cracked   and   grease   it with   a   good   fuel   and   waterproof,   synthetic   grease   like   SuperLube.      To   be   sure   it   closes   securely,   apply   a   thin swipe   of   grease   or   black   paint   on   the   gasket   and   tighten   the   cap.      Remove   it   and   see   if   the   mating   surface   has   a complete circle where the “O” ring makes contact, if not, get a new seal. P erhaps   the   most   common   leak   source   I   see   is   poorly   installed   fuel   vents.     All   vents   should   have   an   anti-siphon loop   just   inside   where   the   vent   penetrates   the   hull.      This   is   a   loop   at   least   one   foot   above   the   vent   outlet   that stops   spray,   rain,   or   sea   wash   from   entering   down   the   vent   hose   into   the   tank.      In   no   case   should   the   vent   hose run   directly   down   to   the   tank.      Another   common   mistake   builders   make   is   installing   the   vents   upside   down.     Most   of   these   vents   have   small   side   holes   with   fine   screens   in   them.      These   holes   must   face   downward   and slightly   aft   to   allow   water   to   drain   out.      You   may   think   because   your   boat   is   new   it   was   installed   correctly, think   again.     We   see   poorly   installed   vents   on   the   finest   yachts   afloat!      Be   smart,   check   yours.     Water   in   the   fuel is   not   as   common   as   asphaltenes,   but   it   can   shut   you   down   faster.      If   you   notice   any   water   in   your   fuel   filter bowls, you can be sure there is more in your tank.
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