Anybody Here Familiar With Pipe Thread Standards?

[Visitor]

This question is kind of electronics-related, since it's about the threads on Chinese flow sensors, and I know there's an abundance of experience here....

I'm looking at using a flow sensor in a project, probably one with connections G3/4" (or possibly G1/2"). Since I'm in the US and we have to do everything our own way, we use NPT fittings. Looking at Amazon and ebay, adapters are available, for about $15 each (so $30 of fittings to connect a $10 flow meter).

It's confusing trying to figure out the exact details of a 'G3/4" ' thread when comparing specs, particularly about tapered vs. straight threads. I suspect G3/4" use a straight thread and an o-ring to seal?

I am in Mexico for a couple more weeks and I've been looking at when threads are in use here. It seems to be a mix of NPT and G threads, so adapters might be common here. One option I see is to get G3/4" female copper sweat fittings and make adapters.

Any good ideas?

 

[rjenkinsgb]

G sizes are parallel, the same as "BSP" parallel threads. The stated size is approximately the pipe bore they were originally used with.

Sealing would be either something like a copper or fibre washer, or a "Dowty seal" which is like a washer with a lipped seal bonded to the internal edge. These have the advantage they do not have to be extremely tight to seal but they can handle extreme pressures.

 

[rjenkinsgb]

From a quick look, G1/2 / G3/4 and 1/2 or 3/4 NPT have the same pitch and nearly the same diameter. Depending which way the adaption is, you may get away with a direct fit plus some loctite or similar thread sealer.

Explanation of common threads including BSP & NPT

Explanation and measurement of common thread standards including BSP and NPT and the difference between them.

www.valvesonline.com.au

 

[Les Jones]

I have attached some information on BSP threads. I think it should give yoy all the information you need on 3/4" BSP dimensions.

Les.

 

[Visitor]

Thanks Gentlemen, that helps my education along. The seal washers are something I've never seen and wouldn't have thought to get if I purchase other fittings.

Here's a picture of the type of flow meter I'm looking at. These things appear to have pretty good engineering for the $10 price. The impeller spins a magnet, which is picked up by an external Hall effect sensor, so no seal to worry about.

 

[Les Jones]

In the UK 3/4" BSP is a common size for the hose connector on outside taps.
This is an example of the hose connector. It would need a rubber washer or "O" ring to make the seal.

Les

 

[Nigel Goodwin]

Thanks Gentlemen, that helps my education along. The seal washers are something I've never seen and wouldn't have thought to get if I purchase other fittings.

Here's a picture of the type of flow meter I'm looking at. These things appear to have pretty good engineering for the $10 price. The impeller spins a magnet, which is picked up by an external Hall effect sensor, so no seal to worry about.

View attachment 130704

Yes, I've played with that exact sensor - it simply connects with the old UK screw-on hose fittings - but everything now seems to be Hoselock, and 3/4" to Hoselock fittings are commonplace.

Here are the ones we use:

https://cpc.farnell.com/hozelock/2175/outdoor-tap-garden-hose-connector/dp/SI15639 there's a rubber seal in the adaptor, so no extra one required.

We don't use the white part, but I can't bring myself to throw them away, so I've got a fair pile of them now. Just don't lose the rubber seal when you unscrew the white part (and not notice) as it WILL leak with out the rubber seal.

 

[rjenkinsgb]

Searching Amazon.com for something to fit the flow meter produces adapters for 3/4 "hose thread" - I think Les has found the compatible fittings, apparently garden hose connections in the US use 3/4" BSP the same as in the UK?

You may also find that a 3/4 NPT barrel connector fits straight on the plastic thread, though?

3/4" is also the standard for bath tap plumbing fittings in the UK - I have no idea what is used in the USA; are those also teh same?
eg.

3/4" Female x 3/4" Female BSP x 300mm Long Flexible Tap Connector / Flexi Tail

Double ended WRAS approved 3/4 inch female to 3/4 inch female BSP x 300mm long flexible tap connector

www.stevensonplumbing.co.uk

22mm x 3/4" BSP End Feed Tap Connector

End feed 22mm tap connector with 3/4 inch BSP female thread

www.stevensonplumbing.co.uk

ps. Those dowty seal washers are intended to go outside the thread of a fitting. Internal washer fittings generally use either rubber or fibre seals.

 

[Les Jones]

Another source of these connections is the water feed hose to washing machines.

Les.

 

[Visitor]

I was just looking at garden hose fittings. Again, the US has to do things its own way.

From Wikipedia:

" In other countries, a British Standard Pipe (BSP) thread is used, which is 3⁄4 inch (19 mm) and 14 TPI (male part outside diameter is 26.441 mm or 1.04 in). The GHT and BSP standards are not compatible, and attempting to connect a GHT hose to a BSP fitting, or vice versa, will damage the threads. "

 

[rjenkinsgb]

attempting to connect a GHT hose to a BSP fitting, or vice versa, will damage the threads.

Doh... I'd see if NPT will fit, at least they are the same thread pitch...

 

[KeepItSimpleStupid]

G3/4 is a US garden hose connector. https://www.supplyhouse.com/sh/control/search/~SEARCH_STRING=garden hose?searchText=garden+hose

 

[Visitor]

G3/4 is a US garden hose connector.

Not so according to Wikipedia, as I posted in post #10.

" In other countries, a British Standard Pipe (BSP) thread is used, which is 3⁄4 inch (19 mm) and 14 TPI (male part outside diameter is 26.441 mm or 1.04 in). The GHT and BSP standards are not compatible, and attempting to connect a GHT hose to a BSP fitting, or vice versa, will damage the threads. "