Leaking pressure vessel, Bali Hai SM 319

John and Anne on Bali Hai <> <hollamby@...>

For many months we have had a whistling sound when running water but
it was not audible when the freshwater pump started. The cause was a
tiny leak from a hole in the pressure vessel located outboard of the
hot water cylinder. This is made of steel and connected to the system
through a brass elbow and copper pipe. The vessel was badly corroded
and a temporary repair made by grinding off the paint around the hole
and applying several coats of Araldite.
An identical pressure vessel was bought for 11 pounds sterling in
Malta from a shop supplying pumps etc for irrigation and we fitted it
with a plastic elbow between it and the brass/copper fittings.
The problem was,I assume,caused by electrolitic reaction.
There is a 2 litre stainless vessel on top of the freshwater pump and
the one behind the hot water calorifier is 5 litres. I suppose its
function is to cope with water expanding whilst it is being heated
although there was only one vessel in the water system on my last
boat,an Oyster.It was one of the few things that never gave trouble
in nine years of liveaboard cruising.
Does anyone know whether this second tank is actually needed and does
it have to be so big as stainless tanks are only available here in 2
or 20 litre capacities.
Anne & John Hollamby