Assistance requested from those that are familiar with DIN38 fittings

[ajoeiam]

Greetings

I've cut outside (not fun but not terrible) and inside (not fun and almost a pita) NPT fittings.

The DIN fittings are quite non-standard here in North America.

Besides the fact that for a DIN38 I need to be able to cut 11 tpi (NOT 11.5 tpi like on some NPT) and that its a 55 degree included thread (our old friend Whitworth) rather than the 60 degree more common for most other things - - - what are the other gotchas.

I need to make a couple fittings termed as insert to DIN38 which means that one end is in a poly tubing and the other threads into my desired valve.

TIA

 

[djc]

DIN38, referenced here: DIN 38:1983-12 1.12.1983 | technical standard | MyStandards appears to have nothing to do with threads.

Any online reference to DIN38 fittings I can find are to something that threads onto a plastic container, that has buttress threads.

However, if your description is correct: 38mm major dia, (1 1/2"), 11tpi and 55 degree thread angle, you would do well to look at BSP (British Standard Pipe) Applicable standard is BS21 (pdf copy easily found online). This comes in both parallel and tapered versions. See also: British Standard Pipe - Wikipedia

 

[ajoeiam]

thank you - - - - -

except I'm now even more confused than before!!!

Looking at : ISO 7 - Pipe Threads where Pressure-tight Joints are made on the Threads and BS 21 - Pressure Tight Pipe Thread Joints

although ( BSPP Threads - British Standard PIPE PARALLEL Thread Dimensions & Specifications ) is very nice.

There is plenty of mention of the tapered thread but all of the world (except Canada and the USA!!!!) uses this for pipe threads but as a straight thread - - - NO TAPER.

ISO 228 - Pipe Threads where Pressure Tight Joints are not made on the Threads - - - is also quite useful

Except there is much ado made of that "pressure tight joints NOT made on the threads" (my emphasis).

So if the sealing isn't happening on the threads - - - - where is it happening?
How many threads do I need on the male side of things so that 'sealing' happens?

Is the sealing from the connection of the shoulder of the female side of the connection to the nut on the male side?

(If this last - - - then I would think that an ORB style of fitting would make a lot more sense.)

Gotta be something out there - - - - all of the world using this system for water handling.

Hopefully someone out there has some ideas.

(this Canada and USA against the rest of the world is getting sorta - - - old - - - you know! - - - argh!!!!!!)

 

[Lloyd-ss]

BSPP uses a seal washer (metal washer with an o-ring molded onto the I.D.) to make the pressure-tight seal. It's basically a straight thread with a small flange on each part and a seal washer in-between. I think.

I totally agree about the USA frustration with the non-metric threads, etc. Over 50 years ago I remember in school talk that we would be converting to the metric system "in the next few years." We totally missed the boat on that one.

 

[Jasonb]

At domestic plumbing pressures BSPP is often sealed with something like PTFE tape or a liquid thread sealer. No Washers, o rings or shoulders

 

[Lloyd-ss]

..................
I need to make a couple fittings termed as insert to DIN38 which means that one end is in a poly tubing and the other threads into my desired valve.

Joe, if this is for non-critical home use, it seems like you could just wing it on the thread faster than you could find and replicate the official spec. After all, it sounds like you have the mating part in your hands already. And if the other end of the fitting is just a hose barb, maybe even make it out of Delrin. I really enjoy cutting threads, but that often means that I put way more time into a threaded connection than I really needed to.

 

[ajoeiam]

Joe, if this is for non-critical home use, it seems like you could just wing it on the thread faster than you could find and replicate the official spec. After all, it sounds like you have the mating part in your hands already. And if the other end of the fitting is just a hose barb, maybe even make it out of Delrin. I really enjoy cutting threads, but that often means that I put way more time into a threaded connection than I really needed to.

That's what is confusing - - - every even sorta 'standard' says that (sorta like) 'don't seal on the threads' yet what I'm hearing is that in practice that's exactly what is done - - - - argh - - - that theory vs practice argument again!!!

I'll source some material and take her from there.

Thanks for the help and suggestions people!!!

Pace (latin for those wondering!)

 

[Lloyd-ss]

Joe, Take a look at DIN ISO 228, size G1-1/8. The major dia is 37.90mm, and its 11 tpi. It might be what you are looking for. It appears to be a British thread that has a DIN/ISO number assigned to it.

Also, here is a very odd application drawing that I found. Tapered male pipe into straight female fitting? This is a joke, right?

You say your valve is a DIN 38, but the 38 seems to be the diameter, not the spec? There must be another spec number somewhere??

 

[kf2qd]

My understanding is that many of the "metric" pipe standards are just a metrification of the BSP data. THere was enough installed stuff out there that it was not practical to convert it to something new, (would have caused chaos) so the metric standard is just metric dimensions on what was an inch item. ANd as far as the US and Canada not being metric? We don't have a problem, and in the machine shop I do some work in each system, though I do tend to convert the dimensions to inch because that is what the measuring tools are. Also - I can get metric and inch brake lines, the fittings are inch.

 

[kf2qd]

Joe, Take a look at DIN ISO 228, size G1-1/8. The major dia is 37.90mm, and its 11 tpi. It might be what you are looking for. It appears to be a British thread that has a DIN/ISO number assigned to it.

Also, here is a very odd application drawing that I found. Tapered male pipe into straight female fitting? This is a joke, right?

You say your valve is a DIN 38, but the 38 seems to be the diameter, not the spec? There must be another spec number somewhere??

View attachment 135623

Yep. A taperred thread will tighten and seal in a straight thread. Maybe no as good as tapered to tapered, but it will work. Somebody really knew what they were doing.

 

[Ken I]

kf2qd - you are right - under the metric system both ISO & DIN they decided not to reinvent the wheel and stuck with the existing BSP & BSPT typically designated like 1/4G in metric drawings - that's 1/4" BSP
However some tables give metric dimensions and pitches which obviously gives weird numbers.
So don't bother with metric tables just use the BSP stuff in inches.
Just a pity that the US decided it had to invent its own (incompatible) NPT.
NP threads are rare in most of the world (but somewhat more common in hydraulics). All non-US pneumatics (Like Festo) are BSP.
The lack of compatibility is a grade "A" PITB

 

[ajoeiam]

kf2qd - you are right - under the metric system both ISO & DIN they decided not to reinvent the wheel and stuck with the existing BSP & BSPT typically designated like 1/4G in metric drawings - that's 1/4" BSP
However some tables give metric dimensions and pitches which obviously gives weird numbers.
So don't bother with metric tables just use the BSP stuff in inches.
Just a pity that the US decided it had to invent its own (incompatible) NPT.
NP threads are rare in most of the world (but somewhat more common in hydraulics). All non-US pneumatics (Like Festo) are BSP.
The lack of compatibility is a grade "A" PITB

Ah - - - the joys of competing standards!!!!!!!!!!
May their promulgatory agencies perish yesterday!!!!!!!!!!!!!!!

What makes this especially interesting is that some European manufacturers use NPT and some use the BSP.
Hopefully not both on the same machine!!!

Have run into equipment where the hardware varied between metric, whitworth and UNC - - - - now that was a royal pita.
Didn't seem to be any rhyme nor any reason to the choices either!!!!!!!!!!

 

[Ken I]

ajoeiam, you should try Russian equipment.

During the cold war the Russians made everything to be compatible NATO to Russian but not vice versa - Russian 155mm shells are a bit bigger they won't fit in NATO guns but NATO ammunition works in a Russian gun.

This paranoia was carried into everything like 67 Volt electrics, fuses and fuse holders - even ball bearings were made off size.

The problem extended into civilian machinery - if you needed anything you would only be able to get the military sized stuff.

I did some work on an ex-soviet vessel and some food processing equipment from the Moscow Food Institute - any breakdown involving anything that would normally be an off the shelf standard item (like a ball bearing) became a nightmare requiring bores and shafts to be machined.

I suspect little has changed. Avoid Russian stuff like the plague.

Regards, Ken

 

[RM-MN]

even ball bearings were made off size.

According to the shop where I take my car to be worked on, bearings are still made off size...even the ones made for that specific vehicle. PITA when the new bearing won't fit and you have the vehicle on the lift.

 

[ajoeiam]

Joe, if this is for non-critical home use, it seems like you could just wing it on the thread faster than you could find and replicate the official spec. After all, it sounds like you have the mating part in your hands already. And if the other end of the fitting is just a hose barb, maybe even make it out of Delrin. I really enjoy cutting threads, but that often means that I put way more time into a threaded connection than I really needed to.

That's what is confusing - - - all the documents say 'not a sealing thread' or some such.
Except - - - that seems to be common practice.

Argh!!!!

 

[HMEL]

thank you - - - - -

except I'm now even more confused than before!!!

Looking at : ISO 7 - Pipe Threads where Pressure-tight Joints are made on the Threads and BS 21 - Pressure Tight Pipe Thread Joints

although ( BSPP Threads - British Standard PIPE PARALLEL Thread Dimensions & Specifications ) is very nice.

There is plenty of mention of the tapered thread but all of the world (except Canada and the USA!!!!) uses this for pipe threads but as a straight thread - - - NO TAPER.

ISO 228 - Pipe Threads where Pressure Tight Joints are not made on the Threads - - - is also quite useful

Except there is much ado made of that "pressure tight joints NOT made on the threads" (my emphasis).

So if the sealing isn't happening on the threads - - - - where is it happening?
How many threads do I need on the male side of things so that 'sealing' happens?

Is the sealing from the connection of the shoulder of the female side of the connection to the nut on the male side?

(If this last - - - then I would think that an ORB style of fitting would make a lot more sense.)

Gotta be something out there - - - - all of the world using this system for water handling.

Hopefully someone out there has some ideas.

(this Canada and USA against the rest of the world is getting sorta - - - old - - - you know! - - - argh!!!!!!)

British Pipe Standard fittings are among the most popular of all foreign threads. These threads come in 2 versions: parallel (BSPP), and tapered (BSPT). The thread flank angle for both tapered and parallel British threads is 55°.

NOTE: It is a common mistake to identify a BSPT (tapered) as an NPT. Remember that NPT threads have a 60° thread flank angle, and BSPT has a 55° angle (this can be verified with a thread gauge). Although BSP is a foreign thread, it isn't metric. This is why it comes in imperial sizes: 1/8, 1/4, 1/2, 3/4, and so on.

• Thread conforms to ISO 228-1
• Port conforms to ISO 1179
• Pitch & diameter measured in inches e.g. G1/4-19
• Parallel threads require o-ring, crush washer, gasket or metal to metal seal between connections for pressure tight connection
• Thread angle is 55°
• Not interchangeable with SAE or NPT(F)

There are political and engineering reasons why standards vary. I copied the above to give you insight as to how the parallel threads are sealed. The tapered threads do not require a gasket. There are a number of high pressure connections that are specially designed for high pressure and do not fall into these categories but that are very expensive and proprietary such as swage lock and a few others I have forgotten.

 

[ninefinger]

I see it alot, even on "engineering drawings" for gas turbine lube systems where the piping and associated fittings are simply referred to as DIN38 or similar, to reference the nominal diameter - similar to saying 1 1/2" pipe. Its not a true full spec as it doesn't define the fitting connection, just the nominal size (i.e. 38mm).

And yes, it is correct to say BSPP does not seal on the threads. Needs a gasket. To confuse matters more see this:

From the Parker Catalaog 4300 - hard copies of these are invaluable for the reference sections (front or back).

 

[Lloyd-ss]

Joe, I might as well add to the confusion, and I will be repeating some information that has already been presented.
First, except for some specialized thread forms, almost all pipe threads do not "seal on the thread", but instead require a specific auxiliary method of sealing. The threads only hold the joint together. Some type of tape or sealant, or an o-ring, or gasket, or a bonded washer, or ferrule, or an integral metal cone (flare) or mating spherical surfaces (pipe union), or some other specialized surface actually makes the pressure tight seal. The reason is because, it is almost impossible to stop the spiral leakage along the thread. Special "dry seal" pipe threads (no sealant required) have carefully controlled crests and roots that deform to make a pressure tight seal on the threads, but even those are only good for a few assemble-disassemble cycles because the metal galls and will no longer seal completely. (The BSPP and BSPT threads are NOT dry seal.)

So, the BSPP and BSPT specify a thread form (shape and dimensions), but not necessarily a specific sealing method. As shown in post #17 and #8 above, the choices are endless and often depend on what country the product was designed and/or manufactured in, not necessarily which spec is the best for the application.

Joe, for your DIN38 (38mm nominal major dia, 11TPI, (G 1-1/8, I think, which does not measure 1.125", BTW)), I would still suggest that you just machine a thread that will fit, and then incorporate either Teflon tape as a seal, or a sealing o-ring that wedges into a recess, to actually make the pressure tight seal. Again, the threads only hold it all together, they do not form the pressure-tight seal. Whenever possible, on unusual sizes and applications, I will incorporate an o-ring into a tapered or counter bored seat because it makes repeatable leak-free servicing possible.
If you look at this subject too closely, for too long, and try to find the logic in it, you could very well jeopardize you mental health. Yikes! Like being forced to read Mil-specs while locked in solitary confinement. The 80/20 rule definitely applies here.
Lloyd

 

[timo_gross]

kf2qd - you are right - under the metric system both ISO & DIN they decided not to reinvent the wheel and stuck with the existing BSP & BSPT typically designated like 1/4G in metric drawings - that's 1/4" BSP
However some tables give metric dimensions and pitches which obviously gives weird numbers.
So don't bother with metric tables just use the BSP stuff in inches.
Just a pity that the US decided it had to invent its own (incompatible) NPT.
NP threads are rare in most of the world (but somewhat more common in hydraulics). All non-US pneumatics (Like Festo) are BSP.
The lack of compatibility is a grade "A" PITB

I usually go to the old lady, she looks at the thread for a split second, she shakes her head or digs out: some adapter, alternative part or matching push fitting for our 8 mm hoses. Sometimes she diggs out a paper cataloge.
Without this kind of expert, it is a pain. "Non-US" pneumatics use all sorts of threads. NPT, G, R ,( "real" metric like M4 M5 M6 for small stuff ) https://www.festo.com/net/SupportPortal/Files/10296/THREADED-FITTINGS_ENUS.pdf
Maybe that link helps at least to find the "standard" to go from there.
I learned that some of the standards are interchangeable, same dimensions but different name. Maybe a look in a tool catalogue?
https://www.regalcuttingtools.com/special-taps
Greetings Timo

 

[timo_gross]

Deleted accidental double post.