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Thread size for heater valve?

Roger K

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Just now, Pete Lewis said:

it seems its   3/8"British Standard Pipe Parallel (BSPP) 


Hmm, that could be right, though I am sure the valve has a tapered thread? Or maybe my memory is playing more tricks.

I can't remember how BSP thread sizes are measured. So the 3/8 is entirelyrley likely


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On 31/12/2020 at 14:24, dougbgt6 said:

Maybe I'm misunderstanding, but the thread I've highlighted says 1/2" BSP and 1/2" BSPT {tapered)

Nobody listens to me :(


Doug, the heater valve on the MkIII threads into the union shown in the diagram as part 6.  That union has one hose fitting cut off (in effect) and the mini-type heater valve threaded directly into it in its place.  That's the thread I was asking about, not the thread for the actual banjo fitting.  It's not shown in that diagram.  Sorry for the confusion!


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On 03/01/2021 at 11:45, SpitFire6 said:

BSPP female for a BSPT thread?

That does not sound right.

Doesn't sound like it's as designed, but from my experience in fluid systems, it does work. I would suggest using PTFE thread tape which will help it seal, lower friction as your thread it in place, and enable you to remove the valve when it fails (if its a new one) and fit the 4-Seasons jobbie. Without thread tape or something similar it will seize given time. A posteriori - which is something similar to what I shouted when it happened to me!

Cheers, Richard

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15 minutes ago, Pete Lewis said:

as a production process the hole would be a straight tapping the fitting a taper 


That sounds right to me - on other cars I have often found a parallel hole, with a taper thread on the component fitted to it.

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