In our short series of introductions to fire extinguisher servicing tools we are featuring the fire extinguisher pump gauge tester which is used by engineers to make sure that the pressure gauge of stored pressure fire extinguishers is operating correctly and is not stuck. In normal operation the needle of the gauge is held in place by the pressure behind the gauge. When the pressure is adjusted e.g. the extinguisher is discharged, the needle moves accordingly. The gauge tester is needed by engineers to make sure that the needle is free-moving and has not seized up over time. The test is carried out by removing a small sticker located on the extinguisher gauge covering a small hole. if the hole does not exist yet, a small hole is drilled by the engineer. The pump is placed over the hole and actioned. This changes the pressure in the gauge housing and the needle moves. If the needle does not move, the gauge has seized up and must be changed. At the end of a test a new sticker is placed over the hole. The colour of the sticker indicates the year of the test.