Simple DIN question

[tbone1004]

I had assumed that these plugs were there to protect the threads and keep the valve from getting knocked out of round, not for containing air.

you can use them for that, but if that is the case, just put the yoke adapter plugs in there. They are used in tech diving to keep high He mixes in the tanks since they like to seep past the valve over time

 

[Luis H]

I had assumed that these plugs were there to protect the threads and keep the valve from getting knocked out of round, not for containing air.

That was the original intention, before helium and tri-mix became popular.

They would help to protect the valves, but I am not totally sure how effective they are at that. The wall on most DIN valves are relatively thin and do not tolerate impact well.
I have a few European valves from the 60’s and 70’s that are out of round and most are missing a lot of chrome in the threads

Even if it is used for this purpose, it is possible for the valve to open accidentally, and pressurize the cavity behind the O-ring.

With a full tank (assuming 3000 psi) you will have a pressure trust of about 995 pounds.

To unscrew the DIN fitting with that pressure trust you will have to apply a torque of about 14.9 foot*pounds.

That is not a huge amount of torque, but it does put unnecessary wear on the threads.

 

[halocline]

With a full tank (assuming 3000 psi) you will have a pressure trust of about 995 pounds.

To unscrew the DIN fitting with that pressure trust you will have to apply a torque of about 14.9 foot*pounds.

That is not a huge amount of torque, but it does put unnecessary wear on the threads.

Gee Luis, couldn't you have been a little more accurate?

 

[WarrenZ]

He could have but didn't know if your valve had ever gotten is threads gaked putting a reg on and if so how bad?

 

[Luis H]

Gee Luis, couldn't you have been a little more accurate?

There is a comedian in every crowd.

The math software (MathCad) that I use for quick calculations like this will provide any number of decimal places that I ask for, but I would never use more than three significant digits. The real world is just not that accurate. The dimensions of diameters, etc. are just not that precise. It is all an approximation.

Posting more than 3 significant digits implies a precision that is not real and in some situations that could be misleading or even unethical.

To be honest, I should have rounded to 1000 pounds of thrust (for the pressure thrust) and about 15 foot pounds of torque, but those particular numbers were just too rounded and made it look just like a guess.

Here a copy of my calculation sheet.
BTW, typing this text takes me many times longer that doing the calculation sheet.

 

[Storker]

What would the result be for 232 and 300 bar tank pressure (3350 and 4350 psi)?

And perhaps a stupid question: Where does the friction in the threads come into the calculation?

</geek>

 

[RainPilot]

What would the result be for 232 and 300 bar tank pressure (3350 and 4350 psi)?

And perhaps a stupid question: Where does the friction in the threads come into the calculation?

</geek>

Simple DIN question indeed, geek.

 

[Luis H]

What would the result be for 232 and 300 bar tank pressure (3350 and 4350 psi)?

And perhaps a stupid question: Where does the friction in the threads come into the calculation?

</geek>

The pressure thrust and torque are directly proportional to the pressure.

With MathCAD, I just retyped the pressure and here are the results.

At 3350 psi: F= 1112 Lbf., T= 16.7 ft* Lbf

At 4350 psi: F= 1444 Lbf., T= 21.7 ft* Lbf


The “c” (or “k” in some references) is the thread coefficient that includes the friction factor. The 0.2 is typical for a non-lubricated threads. The number would go down to about 0.16 (or a bit lower) depending on lubrication. It can also go higher for threads with corrosion or other contaminants.

These are approximations, but they have proven to be fairly accurate for most standard threads.

These thread coefficients do not include thread galling or the extra friction caused by sand in the threads, etc.
Finding sand in DIN threads is a personal favorite for me.

 

[rhwestfall]

If you put one of those plugs in and accidentally open the valve, how do get the plug out?

Piranha has a very interesting one with a push button relief valve (takes a little effort, but nothing like wrenching off a plug). Been using them since last year and very pleased with them. There is also a model with a small hex key plug, but to me, that is too many bits and parts....

edit: I see Luis posted this style plug also...

 

[tbone1004]

Piranha has a very interesting one with a push button relief valve (takes a little effort, but nothing like wrenching off a plug). Been using them since last year and very pleased with them. There is also a model with a small hex key plug, but to me, that is too many bits and parts....

edit: I see Luis posted this style plug also...

small hex key is a more simple plug than the push button and with less moving parts, though you do have to remember the allen key