Thread Size: NBT or BSP

[Tim Good]

Thread Size: NPT or BSP?

I have some bronze values I am replacing. They are from 1996. How do I know if they are NPT or BSP before a stump out a load of cash on new ones?

 

[Heckler]

I have some bronze values I am replacing. They are from 1996. How do I know if they are NBT or BSP before a stump out a load of cash on new ones?

Do you mean NPT?

 

[macd]

NBT?

 

[Tim Good]

Do you mean NPT?

Yes sorry typo. NPT. I've amended the original thread.

 

[Heckler]

NBT?

ok,
NPT national pipe thread american
BSP British Std Pipe
and there is also metric pipe thread
All same size OD, same threads per inch, ie they will all screw together but they have different thread angles.
They will all work together at a push. They will need more sealing gunge that is all!

https://www.google.co.uk/?gws_rd=ssl#q=metric+pipe+thread+size
S

 

[prv]

I have some bronze values I am replacing. They are from 1996. How do I know if they are NPT or BSP before a stump out a load of cash on new ones?

Unless it's an American boat or you have some reason to suspect it's been fitted with American seacocks, they will be BSP. That's what the rest of the world uses, only the US uses NPT.

You might actually struggle to buy NPT over here.

Pete

 

[Tim Good]

Unless it's an American boat or you have some reason to suspect it's been fitted with American seacocks, they will be BSP. That's what the rest of the world uses, only the US uses NPT.

You might actually struggle to buy NPT over here.

Pete

Perfect thanks.

 

[macd]

I'd be interested to know the answer to that question. They're very similar, but NPT is tapered (unlike 'straight' BSP) and the thread form is very slightly different.
Might be easiest to whip a bit off and take it to a plumbers' merchant, see what fits.

 

[prv]

Might be easiest to whip a bit off and take it to a plumbers' merchant, see what fits.

My local plumber's merchant doesn't have anything in typical "boat seacock" sizes. Not much in a domestic heating system that uses 1-1/2" valves

And they're certainly unlikely to have NPT fittings on the shelf.

Pete

 

[macd]

My local plumber's merchant doesn't have anything in typical "boat seacock" sizes.
And they're certainly unlikely to have NPT fittings on the shelf.

Mine does, but he's in Turkey.
Why would the OP need NPT for such a test?: if the existing offered part fits BSP nicely, it's BSP. If it doesn't fit or fits but badly, it's NPT.

same threads per inch, ie they will all screw together but they have different thread angles.
They will all work together at a push. They will need more sealing gunge that is all!

Not quite the same pitch (tpi of nominal 1.5in is 11 in BSP, 11.5 in NPT, for instance), but close enough for a workable length to screw together.

As said, unless US boat, almost certainly BSP.

 

[michael_w]

Hydraulic and automotive suppliers have NPT stuff in stock. Be prepared for eye watering prices...

 

[Tim Good]

Mine does, but he's in Turkey.
Why would the OP need NPT for such a test?: if the existing offered part fits BSP nicely, it's BSP. If it doesn't fit or fits but badly, it's NPT.

Not quite the same pitch (tpi of nominal 1.5in is 11 in BSP, 11.5 in NPT, for instance), but close enough for a workable length to screw together.

As said, unless US boat, almost certainly BSP.

I was just unsure so when buying some new parts where the option is bps or npt I wanted to make sure. See my thread re. Stainless parts from industrial and marine suppliers. The industrial one suppliers valves cheaper but in npt or bsp. I was unsure what it was so thought a new thread might clarify and be useful for others.

 

[Len Ingalls]

http://pipeandhose.com/?q=node/2

For Reference.
Note: NPT T= tapered NPS S= straight or "parallel" as used in proper seacocks in N.America

 

[superheat6k]

NPT is commonly found in the refrigeration industry, due to dominance of American designs - even the Germans make compressors to UNC imperial sizes, and all compressor makers offer otherwise metric machines with imperial pipe connections sizes as standard, and that is now in 2015

According to size the threads do vary by up to 1 TPI compared with BSPT. with slightly differing forms (teeth angles) However if the specific size has a differing TPI with softer metals they will simply distort to fit and can make a more effective seal. I have never found an NPT thread on a boat skin fitting or seacock, although certain fittings on my boats fuel supply system are now NPT.

 

[Len Ingalls]

You are going to need a thread pitch guage to easily determine British or American,I guess.

http://www.adaptall.com/tutorial/idbsp.html

Hope this helps Len

 

[John the kiwi]

BSP - vu

This has been covered before in some detail...

http://www.ybw.com/forums/showthread.php?361441-BSP-not-what-it-seems

http://en.wikipedia.org/wiki/British_Standard_Pipe

 

[Len Ingalls]

This has been covered before in some detail...

http://www.ybw.com/forums/showthread.php?361441-BSP-not-what-it-seems

http://en.wikipedia.org/wiki/British_Standard_Pipe

Thanks John.Very entertaining read.What a mess you folks face.
Glad we are still using N.American system for most common plumbing.
It hasn't been mucked with yet,& adapters are readily available to convert the occasional "weird to us" fitting that shows up on "Euro" eqpt.
We adapt right at the eqpt. & continue from there in N.A std.
Bad enough we had the Metric "standard" system dumped on us.It would be OK,if it was "standardized".
Why do I need 3 thread pitches-2 were just fine-& twice as many wrenches to have one EVERY mm.
Really-what's the practical difference between 10 & 11 mm, or between 13 & 14mm spanners.
Just pick the odd or even mm & chuck the others.
Ducking head & destroying soapbox now-Cheers/ Len

 

[prv]

Thanks John.Very entertaining read.What a mess you folks face.
Glad we are still using N.American system for most common plumbing.

Seems there are some pitfalls with the American system too. Among other things, this US page talks about mismatching taper and straight NP threads: http://www.pbase.com/mainecruising/seacock_primer

Pete

 

[Len Ingalls]

Seems there are some pitfalls with the American system too. Among other things, this US page talks about mismatching taper and straight NP threads: http://www.pbase.com/mainecruising/seacock_primer

Pete

Quite right-N.A. boat builders have not been saints.

However,proper seacocks,with bolt thru flange bases,& for use with NPS (straight) mushroom,(or flush) head thru hulls have always been available,& are the proper items to use,under water,for the reasons given in the excellent article quoted.
There is no "sealing surface" machined into these seacocks,for the NPStraight thru hull to seat against,because you don't want the thru hull to bottom out in the seacock,before the seacock flange is drawn tightly against the inside hull gasket/sealant.
Straight threads are not designed to seal.If any water gets past the outside mushroom head,it simply chases the threads up into the seacock,where it is combined with the normal intake flow.Water cannot escape out between the flange & inside hull,because of the gasket/sealant.

Finally,the seacock outlet is threaded NPTaper,so that a standard NPTaper close nipple,with NPtaper ball valve can be screwed on.
You won't find anything but NPTaper joints,in the system,once you screw the seacock on the NPStraight thru hull.

For above water thru hulls(skin fittings),you can use thru hulls that are NPTaper thread,with a "locking" nut.These thru hulls are available with hose barb inside ends,if you don't wish to have a shut off(stop cock),or they are available in NPTaper,to which you screw a NPTaper ball valve-BUT,they are not approved for underwater.

With GRP hulls,it is not uncommon to build a GRP spacer plate,inst.flat head bolts,with countersinks,& epoxy the plate to the inside of hull,with the bolt threads facing inward.The seacock is set over these "studs" & nutted.This avoids drilling & finishing bolts thru the hull.

Cheers/ Len