NPT v BSP fittings

Gordonmc

Gordonmc

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My boat came with a dogs-breakfast of plumbing fittings, having been built in the US and worked on over the years in France and the UK.
It appears the skin fittings and ball valves are NPT (tapered) in a mix of DZR and plastic hose-tails. Most of the "inboard" fittings have been changed over the years to BSP threaded fittings.
I am now faced with the choice of replacing all the NPT stuff with BSP which is a shame because the skin fittings are in good nick. Most are Groco.
Any source for NPT threaded plumbing bits in the UK?
 
Gordonmc said:
My boat came with a dogs-breakfast of plumbing fittings, having been built in the US and worked on over the years in France and the UK.
It appears the skin fittings and ball valves are NPT (tapered) in a mix of DZR and plastic hose-tails. Most of the "inboard" fittings have been changed over the years to BSP threaded fittings.
I am now faced with the choice of replacing all the NPT stuff with BSP which is a shame because the skin fittings are in good nick. Most are Groco.
Any source for NPT threaded plumbing bits in the UK?
Click to expand...

I think asap-supplies has them
 
ASAP would be my first port of call as well. They certainly have adaptors in small sizes for fuel fittings, I've used those, but I don't know about plumbing sizes.

Pete
 
pvb said:
I always thought BSP worked OK with NPT, as long as it's on low pressure systems such as you'd have on a boat.
Click to expand...

They will screw together as there are identical TPI between the two sizes but the threads are a different shape.

When the thread is made up there may only be a minimum thread engagement which is not as secure. Also the corrosion risk is high with NPT / BSP as the taper gap is as an ideal area for trapping products that cause corrosion.

For these reasons the combination is banned by many companies. A lot of drilling rigs are American in UK waters and this was a constant issue even on so called low pressure utilities such as water supply. There are pictures kicking about of the fittings held together by two thread engagements as the rest have disappeared. This was carbon steel, not bronze or DZR.

I would not recommend mixing threads.
 
They will screw together as there are identical TPI between the two sizes but the threads are a different shape
Click to expand...

Only ome sizes have identical tpi

ITYWF that 3/8" to 3/4" are the same tpi.

1/8" and 1/4" are 1 tpi different so might engage for a short length but then not

1" and above are 1/2 tpi different.

NPT is a 60° thread. BSP is a 55° thread
 
What do you need? I've got a box of 316 stainless NPT pipe fittings in large sizes. I might be able to spare a few (but keeping most for my boat).
 
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