Calibrated tool let down.

[sgtmac]

In the aviation industry we have to have the tools we used for "returning an aircraft to service" calibrated.

Been that way forever.

My issue: nitrogen and oxygen regulators were being sent for calibration as required. I received a note in the last batch of tools that said in the future to please remove the gauges since that is what is being calibrated.

It blew my mind to learn they were not checking or doing anything with the regulators themselves. The cost to calibrate each gauge is around $40.00.

So each regulator was coming back with 2 calibrated gauges and zero done to the regulators for $80.00 annually.

A defective regulator can be a killer. I have since sent the regulators out for overhaul and they all had issues.

Lesson learned!

 

[pstemari]

That's pretty lame. What was wrong with the regulators that the gauges didn't catch?

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[cvairwerks]

We never calibrate a regulator unless the gauge is a permanent part of it. Gauges get removed by our cal lab and are individually calibrated. They are then reinstalled on the regulator, leak checked and the set function checked. Most of ours are capable of handling more pressure than we use, outside of one special case. We have dedicated gear for that work. Regulators by themselves don't need calibration as they do not measure anything. Now sending them for cal and overhaul as necessary is a litthe different matter.

 

[JonnyMac]

Our calibration requirements (legislated) are such that if an item, eg a thermocouple, requires a cal then it can only be done in isolation when its used in conjunction with some thing else, that also needs to be calibrated. So the DTI requires cal too. So i send off 10 thermocouples annually and any of them can be used with the calibrated dti.
So the system as a whole is calibrated.
Given that the regulator valve is dumb regarless of what you do with it, its only the gauge which determines any of the flow.. so really its only the gauge which needs calibrating.. whether the regulator functions correctly is not a calibration issue

 

[67King]

I don't understand what they are supposed to do to a regulator? The gauges, absolutely. But if something changes due to wear or whatever, on the regulator, the gauges will still show the resultant air pressure.

 

[engineer2]

I agree they should be checked and serviced by someone who knows regulators and has a metrology lab. Regulators can leak from various areas, the diaphagm or spring can break or go bad, the safety valve (if equipped) needs to be checked, etc.

 

[67King]

I agree they should be checked and serviced by someone who knows regulators and has a metrology lab. Regulators can leak from various areas, the diaphagm or spring can break or go bad, the safety valve (if equipped) needs to be checked, etc.

Are all of those parts mentioned not upstream of the lower pressure gauge?

 

[bob15]

Never heard of a regulator needing to be calibrated.

 

[pstemari]

Leaks are not going to be revealed by the gauges.

One could test the regulator to see if the pressure is constant for various flow rates and if the pressure is stable over time, but that's not strictly necessary if the output gauge is being monitored.

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[67King]

Leaks are not going to be revealed by the gauges.

I'm not sure why that matters. The widget downstream will not be affected by anything upstream of the low pressure gauge. As long as the pressure available to the widget (in my case, it would be a damper on a remote reservoir) it accurate, it doesn't matter.

Either I'm not being clear or I completely missing something. Admittedly, I'm not sure why the high pressure gauge requires calibration, either.

 

[engineer2]

Admittedly, I'm not sure why the high pressure gauge requires calibration, either.

An accurate high pressure gauge lets you know what you got from the gas supplier, when the bottle is off, and when the bottle is nearly empty. With some oxygen equipment you have to open the bottle slowly because of high-flow cutoffs, to detect accidental leaks.

Sometimes nitrogen or oxygen are used with a pressure booster if the bottle gets low and the aircraft system requires more than what the bottle has (like a 2500 psi nitrogen strut). Then the high side gauge becomes important.

Calibrating everything is likely part of FAA requirements or the user's own quality program. Aircraft service has some stringent quality and safety rules, but requirements vary.

If you need to calibrate the gauges, you may as well send it all to someone who can test the regulator too. Leaks waste material, big leaks are hazardous. A regulator that won't respond *****.

 

[sgtmac]

regulators can go bad, we use oxygen regulators that service 1800 psi bottles. A bad regulator can be deadly.

My point was I understand the gauges get calibrated but was assuming they wer also doing a functional test of the regulator. They were reinstalling the gauges....how were they testing after installing.

 

[cvairwerks]

Ours get reassembled, then attached to a sample bomb with master gauges. The bomb gets pressurized to a couple of different settings and Leak-Tek used to check all disturbed connections. The regulator gauges are verified against the masters and a calibration curve plotted. If the curve is within limits, then it's back to the line shed.