Burst disk question

[ScubaLawyer]

The US Divers valve overhaul instructions I’m using says 90 in. lb. torque for the burst disk. The manufacturer of the burst disk I’m using says 100 to 120 in. lb. torque. I assume (for no other reason that it seems to make sense) I should follow the manufacturer’s guidelines since it’s their disk. Thoughts? Thanks. Mark.

[Bryan]

Not near my log book where I keep that information but both seem really high. .60in lb is what my 1st thoughts are. I would research a bit more though. .. then again there must be a reason the mfg is recommending that number? ?

[ScubaLawyer]

Not near my log book where I keep that information but both seem really high. .60in lb is what my 1st thoughts are. I would research a bit more though. .. then again there must be a reason the mfg is recommending that number? ?

I always heard 60 in. lb too. That's another reason I'm scratching my head. I double checked and sure enough the official US Divers manual for my solid bar manifold says 90 in. lb. No mistake. The manufacture of my burst disk states, "The burst disk safety assembly should be installed using torque wrench at 100 to 120 inch-pounds."

Argh!

[luis]

In the Sherwood valve manual it says 50 to 60 in*Lbs.
Sherwood is primarily an industrial compress gas valve manufacturer so I tend to trust them. Sherwood used to be one of the largest valve manufacturers around. Burst disc are kind of universal and interchangeable between different valve manufacturers.

The 100 to 120 in*Lb seems very high in comparison. Who is the manufacturer?
My first reaction is that I would be more concern about over torque than under torque. Over torque would tend to cut the disc.

I would try contacting the manufacturer and confirming before proceeding.

[antique diver]

My advice would be to try 60 inch pounds (5 ft. lbs... don't confuse the two torque measurements), and if it leaks air around the gasket snug it a little more, to a maximum of the 120 listed by the kit supplier.

Personally, I think 60 inch lbs / 5 ft lbs sounds a little light on the torque value, BUT it can't hurt a thing to try that first. You can always increase it a little if needed to stop a leak. Honestly I never used a torque wrench on that item, just going by feel seemed to work fine.

[ScubaLawyer]

I spoke with the folks at DiveGearExpress who sell the disk. I didn't notice it before because I hadn't opened the package but these disks have the ring and disc affixed to the end of the plug and not separate pieces like I've always used. They say 100 - 120 in.lb. is what they use with these things.

I'll take the approach that engineering is more art than science when it comes to burst disks. I'll also take everyone's sage advice and just start out around 60 and increase torque from there if it leaks.

Thanks for everyone's input. Mark

[Bryan]

USD manual 1976 has no torque specifications for the disc and retainer. Until I took my 1st PSI class in the 80s I tightened them by feel like Bill and don't remember it being a problem. These days I document the valve repairs I do and follow the mfg specs if available. ...Here in Florida you would be amazed at how many valves have double discs or something other than copper used as a disc.

[ScubaLawyer]

USD manual 1976 has no torque specifications for the disc and retainer. ...

Bryan, FYI. Take a look at page 11 of the 'Aqualung Valve Manual Late" in the VDH Catalog section. It specifies 90 in. lb. torque on the single bar dual manifold. It is copyrighted 2007. No worries, I just wanted to prove I'm not as looney as the rest of the planet says I am. Happy Holidays. Mark.

[Bryan]

I didn't look at the on line one. .I have a couple of originals that I keep on my bookshelf for quick reference. . I'm sure you are no crazier than the rest of us!

[Ron]

The PSI course I took had 90 inch pounds for USD valves. I have always done that with no trouble.

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[time2dive]

My Sherwood manual says 55-60 inch pounds for both the 3/8 and 1/2" burst disks. The new Harris burst disk by Sherwood says 20 ft pounds on the burst disk and the Harris valves should be torqued to 20 ft pounds. The strange thing is that Sherwood has discontinued the old 1/2" burst disk and is now only selling the Harris burst disk and is saying we are now supposed to torque the old valves to 20 ft pounds with the new disk. I am worried that I may start stripping the threads in the old valves....Sherwood has NOT responded to my many phone calls about the new burst disks.

The Genisis burst disks that I have are supposed to be torqued to 30 ft pounds.

One manual that I have says the Thermo burst disks are supposed to be torqued to 60-100 inch pounds.

[antique diver]

This is confusing. I would prefer to use the proper torque, and have the tools for it, but with such a wide variation of specs I think I'll just stick to doing it by "feel".

[Bronze06]

I am with Antique Diver on this question. I generally torque them as I find them, to wit, what does it take me physically to unscrew the burst disk bolt housing and when I put them back together I give them a good snug tightening. It has worked well for me for quite some time. 120 in. lbs. does seem a little excessive though.

[ScubaLawyer]

UPDATE - I took the incremental approach. 60 in. lb = leak. 80 in. lb. = leak. Finally got it to hold at around 100 in. lb. (Slightly above the USD valve mfg number and at the lower end of what the seller of the burst disk advised.) BTW they were 5250 rated disks for 3442 HP tanks with a USD solid bar manifold. Your mileage may vary. Thanks again to everyone who contributed info. Mark.

[Bryan]

Thanks for the update Mark