[Alberg30] Vented Loop

[Don Campbell]

The concepts of anti-siphons into tanks are not really  valid thoughts,
because only rarely might there be there a continuous closed column of liquid
to the tank via a vent contiguous with an upper liquid surface . It only
happens when the open end of the vent is under the surface of the lake or
ocean, and then there will probably be an air lock in the tube or pressure in
the tank due to a closed system that will prevent siphoning.  Vents in tanks
are there to allow for pressure equalization when filling the tank so that
there is not an air lock within the tank caused by the incoming liquid. If
there were to be such a situation of the incoming liquid blocking the inlet to
the tank on filling,  then the contents that were attempting to get in to the
tank would increase the pressure of the gases (air) within the tank, compress
the gas, and cause a back spurt. One does not really want this sort of
physical reaction whether it is a water tank,  fuel tank or a waste tank. You
have the choice of a small 1/4 inch copper line to an outside vent or the same
4" big plastic vent that is on the waste system in your house. Vents in waste
tanks also allow air into the system and prevent anaerobic fermentation which
is both more odiferous and usually a more deadly product than that which
occurs with areobic fermentation.
   As for never having an anti-siphon valve, you have had some thought on
anti-siphoning from the designer and from the factory.  Anti siphon systems
are necesary  in the water cooled engine discharge systems and bilge pump
discharge systems because there is a necessity to have an enclosed,
continuous  water column with the ends of the column  at different levels,
which will allow siphoning. Any air into the highest point of the closed
column will break the siphon, provided the high point of the column is above
the highest water level and both  ends of the column may freely drain. It is a
good idea to have the discharge outlets above water lines, which A 30's have,
but if the boat is healed in the direction of the discharge, a siphon may
develop. Be aware of this when having to pump the bilge, or turn the engine
off if either discharge is below the water line... - and check to see if the
system is siphoning sooner rather than later after finishing either operation.

Don

schuylki at vanent.vanebros.com wrote:

> >Believing in Murphy, it seemed like cheap protection.  They are a pain to
> >install in a crowded space, but it can be done.
>
> Relying on an anti siphon valve to keep your boat from sinking seems like
> an invite to Mr. Murphy, too.
> Do we know those things really work? I've never had one.
>
> Michael
> #220
>  +---------------------------------------------------------------+
>  |                This Old Boat by Don Casey                     |
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 |                This Old Boat by Don Casey                     |
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