Vent on Water Tank

[AlexF]

I've been treating my water tank on my narrowboat, which I have only had a few months, but the boat is a Liverpool Boat circa. 1990. I am a little confused as there does not seem to be a vent on the water tank and when I removed the filler cap I could tell that pressure had built up. The tank is built into / part of the bow and as far as I can tell is original. I cant believe that a boat this age does not have a vent and that previous owners have not found this strange. Should it have one? If so how do I go about fitting one. Any advice would be appreciated.

 

Alex

[Alan de Enfield]

Are you sure ?

 

If you didn't have one, I'd have thought, by the time your tank was half-empty the vaccum would be such that either the pump didn't work or your bow would have taken a very peculiar shape

[springy]

As Alan said if you're sure there isnt a vent (there wasnt on mine !) then a vacuum will develop -

unless it is able to draw air slowly around a poorly sealed cover plate - which may draw other

crud in with it if the cover plate is exposed to the weather.

Is the filler flush with deck ? if not then you could remove the cap and drill it to take a suitable

vent - I used the same type as on my diesel tank.

 

springy

[Phil Ambrose]

Listen to Springy, he is talking sense.

Phil

[AlexF]

Thanks Springy and Alan for the comments - Yes there is certainly a vacuum building up, but I have never had the tank less than half full, and I released the pressure, by opening up the filler cap regularly. I cant understand why the boat was built without one. Unfortunately the filler is quite flush with the deck, therefore I would worry about other stuff getting into the tank.

[nicknorman]

Yes, you should fit one! It would be best not to have the vent on a horizontal external surface but without being there it's hard to know what other possibilities there might be. As a last resort you could fit a vent to the cover plate, something like this which raises the vent orifice slightly: http://www.asap-supplies.com/marine/tank-vents/through-hull-tank-vent-bsp-305144 or this one - less rise but with gauze to keep the bugs out http://www.asap-supplies.com/marine/tank-vents/through-hull-tank-vent-19mm-305112

Edited October 9, 2014 by nicknorman

[Murflynn]

Cut a hole in the deck close to the side of the boat and fit a cast brass bulkhead fitting, attach a swan neck made up from 15mm tube and copper fittings.

[bizzard]

Or leave it as it is and connect a 12v air compressor with a pressure switch to the tank, you could then do away with the domestic water pump, and one fine big pressure accumulator too.

[nicknorman]

Or leave it as it is and connect a 12v air compressor with a pressure switch to the tank, you could then do away with the domestic water pump, and one fine big pressure accumulator too.

Force = pressure x area!

[bizzard]

Force = pressure x area!

Well they've been pressurizing fighter plane, stunt planes and probably many other types of aircraft fuel tanks for donkeys years so the engines don't conk out whilst looping the loop and so on.