Blew a 4000psi burst disk at only 3100psi-WTF?

[AbyssalPlains]

the only torque wrench is in your hand

Exactly!

After browsing online stores and hardware stores and automotive stores, all I could find were torque wrenches for much stronger torques than this job requires. (No, I'm not spending a hundred bucks on a digital wrench for a job that I need to do once every five years, if that).

I was referred to a friendly mechanic who has both a foot-pound and an inch-pound wrench. I show up with my tanks and give him the specs, 80-100 inch-pounds (about 7-8 foot pounds).

Hmm, the inch-pound wrench doesn't even start below 120 inch-pounds, and the foot-pound wrench doesn't start below 10 foot-pounds.

So, the situation is like trying to accurately weigh a letter on a bathroom scale.

Alright, the mechanic sets the foot-pound wrench to the lightest setting, and I start torquing the safety assembly into the valve. It gets harder, the wrench doesn't release. I remember the horror stories I read on the internet about ripped bolts using this kind of wrench. Finally, my 20 years of experience as a hobby mechanic tell me that I shouldn't keep going. After all, all we're trying to do here is to get the brass flange of the valve dig into the copper gasket of the safety assembly, but that's all that's needed. So I stop and leave things where they are, thank the good man and leave.

At home, I replace the other safety assembly using the only torque wrench I trust - the one in my hand.

No more torque wrenches for me.

 

[Leadking]

You have the right to install them any way you want. We ALWAYS installed them with a torque wrench to manufacturers spec's and never had an issue.

Not using a torque wrench can cause issues whicht are;

• Being under torqued which will allow the disc to flex under pressure cycles and prematurely wear out the disc
• Over torque the disc which will cut into the surface of the disc weakening it.

If you are a business and do it any other way, good luck with the liability issues!

 

[captain]

You have the right to install them any way you want. We ALWAYS installed them with a torque wrench to manufacturers spec's and never had an issue.

And I have never used a torque wrench and have had only one blow in 50 years and it was one that was many years old.

 

[Lobzilla]

A fishing/luggage scale, a wrench, a ruler, and some simple math (distance from center of bolt to the point where scale attaches on wrench at 90* angle times load on scale) will replace a torque wrench in a pinch. Scale can be replaced by a known weight like a water filled jug to get in the ballpark. Or, put the tanks on a bathroom scale, orient the wrench horizontally and use the weight change on the scale as an indication of how much load you applied at the end of the wrench.

Most people over-torque anything short of a crankshaft bolt when they go 'by feel'.

 

[Leadking]

Don't confuse immediate failure with premature failure. As a wholesale provider of valves to the industry, I am comfortable saying I have probably installed many more safety assemblies than most and never had a failure that I am aware of.

You have the right to install them any way you want. We ALWAYS installed them with a torque wrench to manufacturers spec's and never had an issue.

And I have never used a torque wrench and have had only one blow in 50 years and it was one that was many years old.

 

[idive2]

I found this one at JC Whitney. It is 20 to 200 inch pound range so the
80-100 inch pounds you are looking for would put it right in the middle of
its' range which should give you decent accuracy. JC Whitney is not known
for the highest quality hand tools but for light use it may serve its' purpose.
I used to have a nice Mac inch pound beam type torque wrench that I liked
a lot but it has been gone for years. I was never wild about the clicker type
torque wrenches especially in 1/4 inch drive but it seems the beam type wrenches
are all 0-80 inch pounds. Anyway here is the link for the JC Whitney...

http://www.jcwhitney.com/1/4-drive-dual-scale-torque-wrench/p2007929.jcwx

 

[AbyssalPlains]

I found this one at JC Whitney. It is 20 to 200 inch pound range so the
80-100 inch pounds you are looking for would put it right in the middle of
its' range which should give you decent accuracy. JC Whitney is not known
for the highest quality hand tools but for light use it may serve its' purpose.
I used to have a nice Mac inch pound beam type torque wrench that I liked
a lot but it has been gone for years. I was never wild about the clicker type
torque wrenches especially in 1/4 inch drive but it seems the beam type wrenches
are all 0-80 inch pounds. Anyway here is the link for the JC Whitney...

MIT 1/4" Drive Dual-scale Torque Wrench - JCWhitney

This is great information! Thanks so much!

 

[Lobzilla]

While I posted some poor man's tricks above, I suggest a used Kent-Moore Torque Angle meter from fleabay for those who want to cover a lot of ground with one tool and relatively little money. I got mine for $105 shipped and it covers everything from small screws to fairly massive high strength bolts. It is basically a ratchet extension with a strain gauge and angle digitizer on it. For me, it replaced everything except a massive dial-gauge torque wrench that stands 4' tall; the other 4 wrenches that I had accumulated for different ranges were sold.