Creating Pressure Gauge Calibration Program 1

[delladoug]

I have been charged with creating a calibration program for our pressure gauges (about 10 analog 3D instrument gauges). They are used solely for water surveys. Along with the analog pressure gauges (between 0-100 & 0-300psi), we have 2 digital Telog static recorders which are both calibrated and certified. I have in mind this very bizarre mental image of a pump attached to a tree of pipes with one of the Telog gauges, an analog gauge permanently attached to serve as an approximator, and a valved quick disconnect with which to attach each gauge for calibration. This is not to make our other gauges tracable. We just need to feel as if there is validity to our readings. I believe I could design a contraption similar to the above descibed one. Problem is, I have no idea what kind of pump to use. I thought my supervisor might have an idea (it was his vision & he's the one with the engineering degree), but he said that he was hoping I'd figure it out. I've been doing research and coming up with very little aside from purchasing $3,500 worth of calibration equipment, which is not really an option at this point in time.

 

[unclesyd]

Our primary gage calibration is accomplished using a deadweight tester that is traceable to NIST.
We also have some secondary gauge comparators using special gauges that are referenced against the DW Tester or a high precision Quartz transducer. The comparator is used on non critical low pressure gauges.

Depending on the accuracy required there are numerous DW Testers with varying precision out there.

We have two of this type plus the higher precision one mentioned above.

http://www.ashcroft.com/products.cfm?doc_id=352

 

[danw2]

THere are hand pumps designed to pressurize small volumes, like the bourdon tube of a pressure gauge and its impulse line, for purposes of periodic calibration.

Try Googling "pressure hand pump"

Dan

 

[JR97]

delladoug,

As long as you are only trying to 'verify' the gages and are not interested in fine accuracy it can be pretty easy. I suggest using a hand pump from a hydraulic jack system - about $250 from Grainger or McMaster Carr, capable of up to 10,000 psi. Connect to a Tee. Designate one of your gages as the 'lab master' which stays in the lab and (hopefully) isn't abused. The lab master is considered to always be correct. Connect the gage to be verified to other opening in the tee and pump to the desired pressure. A little better would be to use a cross instead of a tee and add a pressure relief valve to be sure to not over-pressurize your gages. If you want to upgrade your procedure, periodically send the 'lab master' gage out of house for calibration.

I would think you could get the whole thing up and running for about $700.

JR97

 

[delladoug]

would it make a difference whether I was pumping air or water in them?

 

[dcasto]

It gets a little difficult to hand pump 300 psi.

 

[JR97]

As far as the pressure gage is concerned there is no difference betweeen air and water. There will be a bit of residual water inside the gage which may drip out as long as that is not a problem with your system.

 

[delladoug]

Just going about it to get a pretty close idea about the accuracy ofanalog gauges, do you think using a hydro-static pressure pump like the one I've attached would be sufficient? The one I'm looking at does 500 psi. I plan on having it connected to a tee with the test gauge on one side and the option to either cap off or attach our telog (with NIST tracable calibration) on the other side. Does that sound reasonable?

 

[JR97]

The pump should do fine. Be sure to pre-fill your lines with water (to remove air) prior to attaching your gage(s).

 

[sparc]

delladoug (Mechanical) 7 Jan 08 14:04
would it make a difference whether I was pumping air or water in them?

Yes. If these gauges will be used on an oil filled system test with equipment dedicated to and using the same fluid as the process. Don't use water on a gauge in oil service and don't use components in your test setup that contained oil as they will contaminate the gauges. UNLESS, you completely flush and clean the manifold and all associated parts before switching to another fluid, but the time involved makes this prohibitive.

Get yourself a handpump as was suggested earlier for low pressure (up to 100 PSIG) and a Mansfield 7 Greene dead weight tester (old school but still very accurate and reliable) for higher pressure calibrations.

 

[delladoug]

Thanks everyone. I'm kind of on my way to putting together a little program. Have done 2 cycles of testing on most of our gauges, and have figured out how to do the repeatability & resolution uncertainty calculations. Thanks for all your help!