Can I use an LPG fitting to plumb in my diesel heater?

[Kelpie]

E.g. One of these: http://www.screwfix.com/p/mini-ball-valve-8-x-8mm/26184

It's to go with a Refleks heater of dubious vintage. My next question being... I have measured the existing pipe to be 8mm, but is it possible that it could be some antiquated imperial size instead?

 

[PaulRainbow]

E.g. One of these: http://www.screwfix.com/p/mini-ball-valve-8-x-8mm/26184

It's to go with a Refleks heater of dubious vintage. My next question being... I have measured the existing pipe to be 8mm, but is it possible that it could be some antiquated imperial size instead?

I can see no reason why you cannot use the ball valve you linked to.

If the pipe measures 8mm, that'll likely be metric.

 

[penberth3]

If the pipe measures 8mm, that'll likely be metric.

Or 5/16", which is effectively the same as 8mm

 

[Kelpie]

Or 5/16", which is effectively the same as 8mm

That's the sort of thing I'm concerned about! Are 8mm and 5/16" genuinely interchangeable?

 

[john_morris_uk]

That's the sort of thing I'm concerned about! Are 8mm and 5/16" genuinely interchangeable?

There's 0.34375 mm difference. I can't comment on their interchangeability.

 

[VicS]

There's 0.34375 mm difference. I can't comment on their interchangeability.

Much less than that ITYWF

 

[pvb]

They're interchangeable, certainly for a diesel heater.

 

[fergie_mac66]

There is a slight difference and connection can be made using special olives for the compression fittings.

 

[earlybird]

There's 0.0024" difference Probably less than the manufacturing tolerances of the items I'd imagine.
The only "special" olives that I've come across are for 3/4" nominal tube to use with current 22mm plumbing fittings. Maybe others of course.

 

[fergie_mac66]

Lifted from a gas forum








As I understand it, LPG is the only situation where the difference does actually matter! The difference being the wall thickness; 8mm pipe has thinner wall thickness than 5/16".



Externally, both sizes are so close as to be universally compatible with regards to the pipe fittings. The wall thickness of the 8mm tube however is too thin to comply with the requirements of one of the normative documents. It's not PD 5482-3 2005 as far as I can see but I'm certain something somewhere demands a specific wall thickness for seamless soft copper tube used in boats for gas, and only the imperial tube meets the spec. That is why boat gas is still done in imperial


If you look at olives some are copper and some are brass in different shapes you will find some that fit and some that just dont and if you force them they will leak

 

[PaulRainbow]

FFS just buy the valve and fit it.

Why does everything here have to be such a saga ?

 

[Kelpie]

FFS just buy the valve and fit it.

Why does everything here have to be such a saga ?

Well I've been caught out in the past when a plumbers' merchant assured me that their metric fitting was interchangeable with an imperial pipe. And that was likewise on a low pressure diesel system. It doesn't take a big leak to spoil your day!

 

[PaulRainbow]

Well I've been caught out in the past when a plumbers' merchant assured me that their metric fitting was interchangeable with an imperial pipe. And that was likewise on a low pressure diesel system. It doesn't take a big leak to spoil your day!

It's unlikely that you'll have imperial fuel lines on a 70's boat. Do you have imperial nuts and bolts ? No !

In the unlikely event that you do have 5/16" pipework the difference between that an metric 8mm is about two thousandths of an inch. The two interchange.

 

[penberth3]

...As I understand it, LPG is the only situation where the difference does actually matter! The difference being the wall thickness; 8mm pipe has thinner wall thickness than 5/16".

...The wall thickness of the 8mm tube however is too thin to comply with the requirements of one of the normative documents. It's not PD 5482-3 2005 as far as I can see but I'm certain something somewhere demands a specific wall thickness for seamless soft copper tube used in boats for gas, and only the imperial tube meets the spec. That is why boat gas is still done in imperial

The OP is using it for diesel

 

[PCUK]

Just don't over-tighten the joints.

 

[rob2]

Re. imp/metric, when it was the norm to find all the pipe in one and the fittings in the other, I recall that rubbing a couple of thou off the pipe with some emery tape made for a gastight fit - just make a sliding fit for the olive. That'll do fine for diesel, too.

Rob.

 

[john_morris_uk]

Much less than that ITYWF

My apologies I must have slipped on a calculator key!

One inch is 25.4 mm (by definition; it's actually how the inch is defined!)

5/16 x 25.4 = 7.9375 which is 0.0625 mm less than 8 mm not whatever I said before.

Within manufacturing tolerances (as has been said) is a better description?

 

[penberth3]

...One inch is 25.4 mm (by definition; it's actually how the inch is defined!)

It might be now, but inches were around before millimetres. When I was a lad an inch was the length of three barleycorns.

 

[VicS]

It might be now, but inches were around before millimetres. When I was a lad an inch was the length of three barleycorns.

You have been reading too much Wikipedia

 

[PowerSlapper]

E.g. One of these: http://www.screwfix.com/p/mini-ball-valve-8-x-8mm/26184

It's to go with a Refleks heater of dubious vintage. My next question being... I have measured the existing pipe to be 8mm, but is it possible that it could be some antiquated imperial size instead?

Not withstanding the 8mm vs 5/16" debate the valve in question does not appear to be rated for fuel oil or petrol therefore the answer to your question is NO, you cannot use it (safely) for diesel fuel. I have used similar before for fuel service and found them leaking after a few weeks / months. When opened the seals were found to have expanded and no longer provided a seal.