Pipe joins and pipe sizing for heating oil

[nothanks]

I need to re-route the pipe running between the oil tank and my 50kW boiler. I see that inserts are now recommended in soft copper pipe to prevent the pipe from distorting - but these reduce the bore of a 10mm pipe from about 8.6mm to about 6mm. The boiler manual just gives max pipe run info for 10mm (O/D) and I haven't been able to find any other info. Any suggestions on where to find further info or how to do the sums on the effect of a few (6 or 8) 6mm restrictions in an 8.6mm bore?

[Dave Plowman (News]

Don't know anything about oil pipe, but are you saying end feed not allowed?

[nothanks]

Hmmm, after a bit more thought I'm beginning to realise that this is not an easy one. Oil is incompressible so *I think* this means that, to a first approximation, the narrowest bore sets the flow resistance. The cross-sectional areas will vary as the square of the diameters so that means the XSA through the insert is about 49% that of the pipe. In addition to the XSA (and the head) the flow rate will also vary (in some way) inversely with the internal circumference, but this will be a linear relationship (about 70%) and only relevant for the percentage that's restricted, which is insignificant compared to the XSA effect. I'll now wait for someone to tell me about a link to a relevant graph or table ...

[The Natural Philosopher]

flow through pipes is like current through resistors = the longer and also the narrower they are the more pressure drop for a given flow rate.

You need to add the 'resistances' all together. So short inserts wont hurt too much.

The equations that approximate behaviour are friction to the walls. The larger the bore the more cross section area to surface area there is. Surface area is 2?R times length, cross sectional area is ?R²...so volume per unit wall area varies as R...

[Tim+]

Would the use of flared fittings avoid the loss of flow induce by a pipe insert? I guess you?d need a flaring tool but you can?t have too many tools. ;-)

Tim

[nothanks]

OK, I'll need to think some more about that.

Thanks, but that's effectively what I said in the bit you snipped

>

[nothanks]

It would, and that had been Plan A, but I'd discounted it because one of the points (the end of the existing pipe) would be impossible to get to with a flaring tool ... and I don't have a flaring tool

[John Rumm]

Flow resistance is normally proportional to the the product of the length and the per unit flow resistance. So a short narrowing does not have the same resistance as a complete pipe length at the reduced diameter.

I expect you can treat it in much the same way one would for gas pipe sizing where each restriction can be treated as having an equivalent length of nominal pipe. Say a heuristic like, each insert adds the equivalent of an extra 50cm of pipe. (no idea what that length would be for oil though!)

[Tim+]

I?ve no idea how accurate the flaring has to be but I would have thought that as long as it?s ?near enough for the fittings to bolt together the compression forces with mould the pipe into the correct shape to seal.

(Pure supposition on my part. Could be wrong but I?d be tempted to try it personally. Those with more knowledge of flared fittings on copper might advise otherwise).

Tim

[Dave Plowman (News]

I doubt it. I have a flaring tool for car brake pipes. There's more to it than just flaring it out a bit. It forms a sort of nipple on the end.

[Michael Chare]

You might be able to find more info from Danfoss as they make many of the pumps, or Reillo.

The manual for my Camray Heatslave boiler has details for 10mm and 12mm OD pipe. The max pipe length depends on the head, i.e. how much the bottom of the tank is above or below the oil pump. I used flare fittings when I installed a new boiler some years ago now. It may be that you can flare the end of the pipe before pushing it into its final position. I recall bending my pipe round a small pulley wheel.

The new boiler came with compression joints for the oil supply flow and return.

[Michael Chare]

For 10mm copper oil pipe there is no such nipple the nut that goes onto the pipe first has a female thread which screws into the male thread of what ever the pipe is connecting to.

[nothanks]

I haven't found any info about "equivalent length", or any quantitative guidance, but the boiler manufacturer doesn't foresee any problems so I'll stop thinking about it. It's been pushed-down the job stack by other things but I'll plan to get to it in the warmer weather in case there are problems.