"BigWallop" wrote in message
k...

"stevet" wrote in message
...
Hi

I've been helping a friend get her canal boat 'ship shape' and the
heating
sytem is most odd, there's a log burner with some sort of back boiler
and
pipes that run from one end of the boat to the other, via the
radiatoirs.
The pump (a small 12v affair) is at the rear in the engine bay and there
is
a loop of pipe that goes up and over before going to the inlet of the
pump.
This loop seems to alway get air in it, it does have a bleed valve but
it's
a pain to keep having to bleed it. Also you have to bleed it with the
pump
off otherwise the pump just sucks more air in.
My question is this, can I put an autmatic vent valve onto this loop,
bearing in mind it's on the inlet side of the pump and only 6in away
from
it, or will it just result in more air being sucked into the system. If
it's
not a problem then it will make life easier in keeping air out of the
system.

many thanks

STeve



The little rise in the pipe is actually there to catch the air bubbles,
before
they get to the pump, and bleed them off. It might actually help to
extend the
pipe, that the bleed nipple is on, further up. The extension will catch
more
bubbles at a time, and should make it easier to bleed the system of all
the
bubbles at one time.

Why does it actually need to be bled frequently anyway?

A stupid suggestion?
A canal boat is probably rarely in rough water?
So why does the system have to be a closed loop? Could it not be an open
system with a small 'header' tank at the high point in the system? Any air
in the system would circulate to the high point and 'bubble off' to be
replaced by water through gravity?