Calibration of contents gauge /SPG

[Jules]

Been sorting out some kit today and attached a contents gauge that i haven't used since it was given to me on a pony reg by a friend.
It didn't leak but it only said 150 bar when the three other gauges I tested all said somewhere between 190 and 200 bar. So I am fairly confident that the true value ought to be say 195 bar plus or minus a bit (10% ?)

So the question is when you get your regs set serviced do they usually check the contents gauge and it's accuracy? And can it be adjusted to put back into spec? or do most people just throw them away when the variation from the true value becomes unacceptable.

Does anyone know if you would expect a variation like this to be linear over the range of the gauge? ie if it reads 75% of the "true value" at 200 bar then would this be the same at 100 bar and 50 bar whre you might expect it read 75 bar and 37 bar respectively.

I just realised that I have no idea how they work, so please enlighten me.

Jules

just noticed the appearance a new smiley, it ought t obe called jules and jeremy

[Digger]

At £30 for a new gauge, it can't be worth it can it?

I regularly check my gear to make sure the needle doesn't stick, and that it reads what I expect it to, but I don't remember anyone telling me a gauge was incorrect after service.

It works by having a tube which is all curled up, and when the pressure comes through it straightens the tube very slightly, which causes the needle to move. It must be on google somewhere with the insides exposed. Inaccuracy probably caused by the tube either not straightening enough or straightening too much.

Digs.

[Jules]

At £30 for a new gauge, it can't be worth it can it?

I regularly check my gear to make sure the needle doesn't stick, and that it reads what I expect it to, but I don't remember anyone telling me a gauge was incorrect after service.

It works by having a tube which is all curled up, and when the pressure comes through it straightens the tube very slightly, which causes the needle to move. It must be on google somewhere with the insides exposed. Inaccuracy probably caused by the tube either not straightening enough or straightening too much.

Digs.

Yeah I know but I didn't get to be an engineer without spending a lot of my formative years taking things apart to see how they work (and then hiding the bits when putting them back together again was slightly too hard)

Thanks for the description, I did google but didn't find the answer. That sounds familiar now.

I had an SPG stick once, I thought my SAC had improved dramatically until i realised that it hadn't moved in 15 minutes... a quick tap and it jumped down 20 bar !

[incapete]

I made the mistake of buying a Beaver gauge which reads too high at high pressures and too low at low pressures - at least compared to a Suunto gauge attached to the other post of my twins.

[RogerViking]

another beaver best buy 'at 0 your still sucking gas for ten mins' did it cost extra

[scubacoach]

Within EN250 there is a limit or differential of pressure a gauge should read to the pressure held within the cylinder. This is somewhere between 5 and 10 bar depending on the pressure in the cylinder and the range it covers.
Also as most gauges are are not meant to be opened how do you hope to open adjust and reseal one of the plastic bodied gauges.
Best to buy a decent one in the first place and definitely not a button one.

[fade]

Sadly if it's not reading right then you really should bin it, i'm pretty sure that you cannot adjust them due the design.

Pete

[Jules]

Also as most gauges are are not meant to be opened how do you hope to open adjust and reseal one of the plastic bodied gauges.

Yes I was just wondering whether it was checked when the regs are serviced.
You are only going to know it's out when you compare with another one or two or three ...

[Jules]

Within EN250 there is a limit or differential of pressure a gauge should read to the pressure held within the cylinder. This is somewhere between 5 and 10 bar depending on the pressure in the cylinder and the range it covers.

ah good i assumed there would be spec and assumed that plus or minus 5% was probably about the best uncertainty you would expect so that ties up with my thinking.

[JasonP]

I made the mistake of buying a Beaver gauge which reads too high at high pressures and too low at low pressures - at least compared to a Suunto gauge attached to the other post of my twins.

How do you know the Beaver one is wrong and the Suunto is right?

Man who wears two watches never knows time.

Jason