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N. Thornton wrote:

(Stanley Spanner) wrote in message . com...

Also: it's a gravity feed system and it'd be easier to arrange the
pipework with a rise & fall to accomodate the filter and a butterfly
valve, as below:

________
| |
| tank |
|________|--- ___________
| ___?_ | |
| | | | |
-------------------------- ---| appliance |
|___________|

Should I have an air bleed at a high point in the pipework? (the point
marked ?)
Or should I try not to have a fall at all (do-able, but awkward).

I believe that would be fine as youve drawn it. All that matters to
the oil is the relative heights of start and finish, and length of
pipe. Sharp bends would add more resistance to flow. As long as your
high point is below the top of the oil in the tank there is no
problem.

I used to think so, but it sadly proved not to be the case. I still do
not understand why, but with an arrangement very similar to the above, I
had to suck the bloody stuff through. Total drop of 1.45m over 50 meters
of pipe, and as far as I knew only down underground then up to the
fliter/boiler. All I can sday is that with air in it, it would not flow.

Regards, NT