weber is right, i would never keep anyining in my guages. i have been told in a coarse that you can uncallibrate guages by keeping a longterm charge in them. cross contamination is also an issue as well, if you keep a compressor (air) in you r truck you allways drain it down due to moisture and longevity of the machine . i think gauges are the same. what is the rational for keeping a charge in them anyway?