jointing oil fittings

[Stanley Spanner]

What's pukka for jointing fittings (compression and straight threads) for heating oil? I heard that PTFE tape was not OK. My Purimachos green stuff says it's OK for oil but I wonder if it'd be that effective - I don't think it gets thick and sticky over time like the white stuff.

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).

tia

Stan the Span

[N. Thornton]

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.

Regards, NT

[Stanley Spanner]

In theory :-)

I usually put some green stuff on even new joints, and always on old ones - belt & braces.

- or there's [been] a bit of grit in the joint, which has scored the metal surfaces so they don't seal perfectly. (That's with those of us who don't plumb in clean-room conditions :-)

.. and soft-as-butter fully annealed table Y tube

What about parallel threads? (The filters and butterfly valves all have these.)

Normally I'd use PTFE: the panel at Plumb Center reckoned that was out for oil; but I've just checked Treloar who says "Petroleum resisting compounds and PTFE tapes which remain slightly plastic make the most satisfactory joints; hemp and hard-setting jointing compounds should be avoided". I assume he means PTFE tapes in general, not 'Petroleum resisting PTFE tapes' as I understand PTFE is pretty inert stuff and I doubt it would be bothered by heating oil.

OTOH he also says soft soldered joints are out, which means I've got more &%^* compression joints to make on soft tube :-(

cheers

Stan the Span

[The Natural Philosopher]

Compression, but beware that they are weak at the normal pipe diameter. PTFE tape doesn't work well - use Red Loctite to seal. Try to avoid up and under routing - you will just have to bleed it - don't put bleed valves on, just steel yourself and suck the bloody pipe full and then never ever let it run dry again :(

[The Natural Philosopher]

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.

[The Natural Philosopher]

I repeat, common sense is on your side, bitter experience - or rather diesel tasting experience, is on mine. On a long run, any uphill run is a problem, no matter what the final height is. Once full of oil, both my pipes ran freely under gravity, and no point in the pipe was above the final outflow point. BOTH refused to flow with air in the pipes. I do not understand this either.

[N. Thornton]

Plstic bag loosely over end of pipe before sucking would make life less unpleasant - but I can just imagine some incompetent person breathing the bag up and choking. So I'd best say dont.

Regards, NT