How to choose the appropriate pressure gauge to meet process & I&C eng

[hswang2]

We process engineer deign a pressure gauge installed on the process line (liquid phase, line pressure is min op= atm, normal op=1 barg,max op=12 barg, and design pressure=25 barg).
But, the I&C staff came to me and said this pressure gauge maximum op should be within the two third of the maximum full scale of the gauge. So in this case max op should be 2/3 X 12 barg=7.9barg instead of 12barg.
As I know every pressure gauge have an inherent over range generally 1.3 times the maximum full scale value of the gauge.
My question is how to fix the I&C staff problem to choose the appropriate pressure gauge and also meet process staff requirement max op=12 barg.(for example put two pressure gauge)
Thank you very much.

 

[JohnGP]

hswang2,
My experience is that maximum operating pressure should be within 75% of gauge maximum reading, so in your case a gauge that reads up to 16barg should do the job. It depends on the application though - if the process pressure is steady, then 16barg is Ok, but if pressure is fluctuating continuously, then I would go with what your I&C staff are saying, and choose a gauge that has a full scale reading of at least 18barg, or the next largest standard range available to you.

Just my thoughts,
Cheers,
John

 

[JLSeagull]

Several pressure limiting issues apply to bourdon tube pressure gauges. One serious limit is the gear mechanism that turns the pointer. One over-range point exists where the large gear runs past the small gear. This may be closer to 125% of the scale range. You can repair the gauge when you overrun the gears but it is better not to exceed the mechanical travel.

It is desirable for the normal pressure to be in the middle third. I prefer not to select a gauge with the maximum pressure higher than 90% of the reading. It is OK for the maximum to be near 100%. Don't go beyond this as a spike in pressure (water hammer for example) could put you over the top.

 

[rmw]

I interpret what the I&C staff has requested to be what JohnGP has suggested.

rmw

 

[hswang2]

Dear all
Thank you very much for your kindly help.
As I&C staff told me that it is hard for them to find
the pressure gauge for the noraml op=atm and max op=12
The reason is it could not be seen clearly in this PG as it's op =1 barg
.