what is difference between NPT (National Pipe Taper) and BSP (British Standard Pipe)? I know that they will screw in and tighten up. Does the BSP need a washer to seal
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what is he difference between NPT and BSP
- Thread starter kk4iz
- Start date
The BSP thread is actually a straight pipe thread and not tapered. It's seal is created with a rubber washer or o-ring at the base. The depth is also controlled to the flat section where the seal mates. With the NPT, its seal is created by the mechanical wedging of the threads in the taper. A bit of sealing tape helps with the imperfections of the thread cutting process.
Another thing, in the under 1/2 inch sizes the thread pitch is different by one per inch. In the case of 1/8" (the common one seen on airgun fittings) the thread pitch for the BSP is 28 while the NPT is 27. Both the 1/4" and 3/8" are 18 and 19 respectively for the two thread forms. Besides the pitch, the thread form is also slightly different. The British use the 55 degree Whitworth while the American standard is the 60 degree Unified form.
While these appear to screw into each other, they really will not seal properly, nor will they have the same strength. You are not holding by all the threads. Part of the thread has full engagement, but then the engagement decreases until there is none at all. The ability to hold pressure goes way down.
Another thing, in the under 1/2 inch sizes the thread pitch is different by one per inch. In the case of 1/8" (the common one seen on airgun fittings) the thread pitch for the BSP is 28 while the NPT is 27. Both the 1/4" and 3/8" are 18 and 19 respectively for the two thread forms. Besides the pitch, the thread form is also slightly different. The British use the 55 degree Whitworth while the American standard is the 60 degree Unified form.
While these appear to screw into each other, they really will not seal properly, nor will they have the same strength. You are not holding by all the threads. Part of the thread has full engagement, but then the engagement decreases until there is none at all. The ability to hold pressure goes way down.
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While most people think parallel threads when BSP is mentioned (actually BSPP), it does come in a tapered version too (BSPT), like NP comes in NPS and NPT.
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OK now where do you find the seal washers or o-rings. I know it has to be machined for the o-ring, there is a small plate place to seal with a washer but don't thank it want hold an o-ring.
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