Calibration

The number one reason for failure in gauge accuracy is hand twisting the gauge into a fitting. This turns and misaligns the movement inside the case, ruining any chance of calibrating. Always use the proper wrench and do not over tighten. Failure to use and open a bleeder when a hydrant valve or similar system is being closed can quickly over pressurize a gauge, stretching the bourdon tube, damaging the gauge. Pressure gauges are precise measuring instruments and subjecting them to extreme cold or rough use quickly reducing the accuracy. Gauges read more accurately in the mid range than on the extremes of the dial. The maximum operating pressure should not exceed 75% of the full-scale range. The normal operating range should be in the middle half of the range whenever possible. If a gauge is off the zero indicator sometimes it can be corrected by venting. Venting is done by placing the gauge upright and opening the rubber vent cap at the top of the case. If the atmospheric pressure inside the case is different from the outside, many times the needle will be off zero. Liquid filled gauges sometimes may leak (weep) some fluid, especially during flights. The gauges do not have to be full to work properly. Gauges do not come from any manufacturer with individual certification. Certification ensures accuracy and is necessary for certain types of testing. Certification is normally done on an annual basis.