Force vs Pressure vs Surface Area and Tank Valves

[Ghost95]

Because I want to.

Morning all, I hope you are doing well.

I'm back at work and that gives me time to ponder things. Things like splitting my vintage doubles and getting a more ergonomic valve on a 72 I have. I was wondering about the safety of machining a 3/4" valve down to a 1/2" NPS thread to fit those old vintage tanks with that thread. Sportsways, White Stag, ect.

Anyway, in thinking about this I was wondering if a 1/2" valve is inherently stronger than a 3/4" valve because of less surface area at the base of the valve. Is more force applied to a 3/4" valve with 2800 psi behind it than is applied to a 1/2" valve with 2800 psi? Assuming a competent machinist, would reducing the diameter of a 3/4" valve to 1/2" NPS threads be safe? Would there be an issue bechause the hard chrome was removed in the process making the threads contact surface brass?

I'm not sure it's worth the expense to most people, maybe not even to me but I'm just wondering about the possibility of the operation.

Thanks for your insight. Have a good day.

 

[rjack321]

3/4" valves don't break even when hydro pressures are applied (5000-5250psi+ that's how burst disks burst) so whether 1/2" is stronger or not is not really relevant.

It's not hard to turn them down to 1/2"

 

[Julius SCHMIDT]

I've recut a few valves that were incorrectly or sloppily cut, too thick chrome, too much variation between valve and tank I was putting it into, but leave the bit at the top for an Oring and make really really sure the "technician" doesn't treat your valve like farm equipment and marr and damage it

 

[Ghost95]

3/4" valves don't break even when hydro pressures are applied (5000-5250psi+ that's how burst disks burst) so whether 1/2" is stronger or not is not really relevant.

It's not hard to turn them down to 1/2"

No issue with the valve threads being exposed brass instead of hard chrome?

 

[rjack321]

No issue with the valve threads being exposed brass instead of hard chrome?

CGA valves are not chromed and even if they were, chromed NPT threads would be a bad idea. Too easy to flake off a fleck of chrome and cause problems in the tank

 

[Ghost95]

Thanks. If I pursue this I'll be going to NPS threads, the non tapered ones. I guess that wouldn't make much difference though.

 

[rjack321]

Thanks. If I pursue this I'll be going to NPS threads, the non tapered ones. I guess that wouldn't make much difference though.

I missed the "S" in the original post but 1/2" NPS? I don't think those were (ever?) made. Lp72 tanks of the vintage had 1/2" NPT threads so they take Teflon tape not straight thread Oring seals. Do you have the tank and what valve is in it now? Any pictures of the tank and valve?

You definitely cannot have a NPT tank tapped and rethreaded to anything.

 

[Bob DBF]

I missed the "S" in the original post but 1/2" NPS? I don't think those were (ever?) made.

They were for a short time by a manufacturer before 3/4 NPS, which became the standard for obvious reasons. I've got an old 1/2 NPS valve laying around, but I've only seen one tank with that thread, but there weren't a lot made.

Edit
Check out this thread for more information:
1/2in NPS valve required for 72
Old Walter Kiddie find With 1/2” straight thread valve

 

[NAM001]

I believe the 1/2" is stronger and has less force on the threads its a pie r square thing

 

[Bob DBF]

I believe the 1/2" is stronger and has less force on the threads its a pie r square thing

Right on with the force on the valve base. As far as strength of the valve, it's probably the same alloy as all the other HP valves.