Valve to cylinder torque

[nikolay_zhelev]

Hi guys,

According to the manufacturer instructions of my valve the specified torque for steel cylinder installation with 25x2 threat is 100-130 Nm.

Is that correct amount of torque for valve istallation? To me it looks too much. My car wheels are tighten with this amount of torque.

My cylinder is steel faber cylinder, 3L, 232Bar.
The valve is MDE pre 2008.

 

[jfe]

........... My car wheels are tighten with this amount of torque..........

That was my first thought, it seems way over the top. Here is a quote from Dive Gear Express website (if I may):
Valves should be installed in scuba cylinders with the least amount of force that will form a seal and retain the valve in place. For modern valves that capture an o-ring between the neck and the valve, this usually means they can be installed by hand and just snugged up with a hand wrench across a flat at the base of the valve. The threads should not bind and force is NOT required to fully screw the valve home. Do not use the wrench across the face of the valve, do not over tighten and do NOT bang on the handwheel. One important caution regarding thread compatibility; outside the United States, particularly in Europe, a widely used SCUBA cylinder neck thread form is known as M25. The 3/4 NPS (ISO 228) and M25 (BS 3643) threads are very similar but not identical; with the use of excessive force it's possible to mate diving cylinders and valves with these two different forms. However, the mismatched threads eventually separate with dangerously explosive force, often causing injury.

 

[divad]

Yikes...I wouldn't even have thought of this. Thanks.

I've always just spun them in and bopped them with the bottom of my fist.

 

[decompression]

Wow, ya, just a light tap with a rubber mallet.........mmmmm.

 

[Aviyes]

Since we are using o-rings, we should be talking a torque requirement of in-lbs (N-cm). I would double-check that spec from your manual.

 

[Pao]

My lug nuts torque to 110 Nm. That is definitely excessive. This is for Al tanks. From LUXFER’S SCUBA CYLINDER VISUAL INSPECTION GUIDE:
"Without a recommended torque from the valve manufacturer, we would recommend
a torque of 50 lbf-ft, plus or minus 10 lbf-ft. All torquing should be done such that
valve, valve components and cylinder are not damaged."

 

[Pao]

From Serwood's Assembly & Maintenance Guide

VALVE TORQUE SPECIFICATIONS
Valve into cylinder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40-50 ft. lbs.
Bonnet nut into valve body . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-15 ft. lbs.
Burst plug into valve body . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50-60 in. lbs.
Double manifold center section nuts to cylinder sections . . . . . . . . . . . . .10-12 ft. lbs.

 

[Rred]

Nick-
Rashly assuming that the manufacturer knows what they were doing, and that your tank and valve are both of the same type they are presuming, I'd tend to say "Do what they said."
Every dive shop seems to think the "right" way to deal with valves is to give the valve a whack with a rubber mallet and then do the rest by hand. (Or hand tighten and then add a whack.) Me? I don't give a damn how they say the valve is built, I was taught that you just don't go whacking valves that way, it tends to upset the moving parts.
I confess, I'll try to lock my legs around a tank because I don't have a handy chain vise on a workbench--but that's no excuse for someone in the business. And using a big crowfoot wrench on the flats at the base of the valve shouldn't be beyond their ability either.
But then again, if the first 20 years after I got my torque wrench, I only came across *two* auto shops (dealers, tire stores, annual inspections, all of that) that properly torqued a wheel bolt. Everybody else just does what the dive shops do: Whatever is convenient.
And fortunately the tanks and valves are so robust they seem to take that abuse without going kaboom very often.

Don't forget--if anyone has applied thread compound to the tank neck? That changes the torque spec, too. Ask the manufacturer whether they've anticipated that, too.

 

[TrimixToo]

I thought tank valves used one of the two Universal Torque Specifications:

- Until it strips, and then another quarter of a turn.
- (For the Germans) Guten tight.

 

[nikolay_zhelev]

Hi guys,

Thanks for all replies!

The given torque value is from the valve manufacturer and also there is a standard ISO 13341 - Gas Cylinders - Fitting of valve to gas cylinders and inside in Appendix A the same torque value is given.

I've always been taught to follow manufacturer recommendations, but I would like to understand why such huge torque is required for tank valve with M25x2 threat? Am I missing something between the lines, like "use specified torque if no o-ring is inserted" or something similar?

I'm sure here there are dive professionals who have been trained to service tanks, so if possible please share your experience, have you ever torqued valves to 100-130 Nm?