Pressure gauges – calibration screw

What is a calibration screw?


Analog pressure gauges are one of the most common and simple instruments used, but they are also common to errors; usually being out of tolerance or the needle not returning to zero, often due to environmental issues. However, some analog pressure gauges are easily adjusted. A calibration screw is often used as part of the design to correct ‘faulty’ analog pressure gauges, although not all analog pressure gauges have a calibration screw


Calibration screws are found in certain places:


  • On the dial face itself
  • Adjustment knob on the lower side of the gauge
  • A screw on the needle, either in the center or just to the right.


Dial face


Some pressure gauges have a screw on the dial face, either behind the needle or by the scale of the gauge. To access this, remove the cover and the window. Then either turn the screw clockwise or anticlockwise to return the needle to zero.


Adjustment knob


Some pressure gauges have an adjustment knob on the lower side of the pressure gauge. Often this has a lock on it, which needs to be removed, the needle will then move freely once the knob is turned and the needle can be returned to zero.


Needle with calibration screw


Other pressure gauges may have an adjustment screw on the needle itself. The cover and window need to be removed and a screwdriver used to turn the needle into position. You must hold the needle still while turning the screw and it must be done carefully as the needle is connected the spring and is very sensitive. The gauge could become permanently damaged if care is not taken when performing this adjustment. Once the adjustment has been made, the pressure gauge must be calibrated to ensure all errors are now within the acceptable tolerances.


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