Hypothetical question - BSP threads

[Tim W]

Just ordering some stuff from BES and browsed into the gas cooker bayonet section.

They sell a kit of parts that contains:

1/2" standard cooker hose kit. Kit No.1 consists of : 6038 4' x 1/2" bayonet cooker hose 6775 15 mm end feed x 1/2" BSP T straight male adaptor, brass 0621 Plug-in angle socket 6048 Angled wall connector 9543 Cooker stability chain 7452 Wall plug, brown x 2 6366 F x F 90°elbow, malleable iron 10994 Pozi woodscrew x 2 6377 M x F 90°elbow, malleable iron

0621 is one of the usual 1/2" BSP-taper jobbies. Fine. But the bit to which it connects, 6048 is described here:

a parallel thread.

I *thought* one should use taper to taper BSP or parallel to parallel and not mix taper with parallel.

Especially as the same page has many similar wall connectors with taper threads.

What gives?

And why do they lob a couple of iron fittings in?

[Tim W]

Tim W wibbled on Tuesday 20 October 2009 22:57

OK - just worked that one out - presumably for the host to cooker attachment...

[Onetap]

The male threads taper, the female are parallel.

[Tim W]

Onetap wibbled on Tuesday 20 October 2009 23:33

OK.

So when would you use a male-taper *and* a female-taper together?

Cheers

Tim

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Tim W saying something like:

Fwiw, I can't recall a single one like that.

[Bob Minchin]

You don't!

Bob

[Tim W]

Grimly Curmudgeon wibbled on Wednesday 21 October 2009 07:01

So presumably, you might also use (in other contexts, perhaps a water tap) a parallel male into a taper female?

For some reason, I'd always assumed taper male and female went together...

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Tim W saying something like:

Yes, that would work. Of course, either way there's a risk of straining the two or three threads that are doing the work, if overtightened.

So did I, but as I say, I can't recall ever having encountered a joint like that, but I stand to be corrected. Maybe it's perfectly acceptable

- indeed, if the tapers are a good fit the risk of straining the threads would be reduced if the load is spread more evenly. However, the cheap and nasty fittings don't seem to be that well made and I'm ambiguous on the matter.

The problem I see with it, is a slight unscrewing action would have the tapers completely disengaged - not good at all.

[Tim W]

Grimly Curmudgeon wibbled on Wednesday 21 October 2009 12:08

Perhaps that's it? Never though about it like that before...

[Baz]

First Choice would be Male Taper and Female Taper. Second Choice would be Male Taper and Female Parallel. Male Parallel to Female Taper. Is a bodge and only if you have too. Male Parallel to Female Parallel is fine, as long as the correct type of seal is used. And you don't have to line anything up.

Baz

[Tim W]

Baz wibbled on Wednesday 21 October 2009 14:01

That's what I thought...

It would be interesting to hear a GasSafe take on this (hint ;-> ). It is presumably valid if BES are selling kits like that... But I'm still a little puzzelled - especially as now there is a slight divergence of opinion here.

That would be "I've run out of tap connectors, but I've found something that sort of fits!"

Aka taps.

Interesting...

Cheers

Tim

[Baz]

BS21.

Standard No BS21:1985 Title of Standard Specification for pipe threads for tubes and fittings where pressure-tight joints are made on the threads (metric dimensions) ISBN 058014556 5 Date of Publication 30/09/85 Approx Pages 20 Description Threads, Pipes, Parallel threads, Taper threads, External threads, Internal threads, Screwed fittings, Pipe fittings, Dimensions, Dimensional tolerances, Designations, Pressure pipes, Thread gauges, Longscrews, Gas-powered devices, Pipe couplings, Thread Cross references BS 919:Part 2, BS 1387, BS 2779 International Equiv (If Applicable ) ISO 7-2:1982 Replaces Standards : BS21:1973 Replacement Notes Now Replaced By BS EN 10226-1:2004 Replaced by Notes Partially replaced by BS EN 10226-1:2004. Committee Ref ISE/9

[John Rumm]

The point of taper (no pun intended!) fittings is when you want a seal on the threads - hence you want to create an interference fit at some point in the assembly process, so your sealing tape can do its stuff. This can be done most commonly by screwing a taper male into a parallel female. The reverse would also work however.

Presumably for when you have a vertical pipe run to the bayonet fixing.

[Tim W]

John Rumm wibbled on Wednesday 21 October 2009 20:08

>

Thanks John. Isn't it weird how you can go round with a notion and never question it.

I've done plenty of BSP taper joints - just never had to actually buy them (ie re-did ones that were in place or put together bits someone else had bought...)