PRESSURE MEASUREMENT INSTRUMENTS © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

 Hello, I want to show you the various pressure measurement gauges we use at Fresh or Freezing and talk about how we maintain and test them.  Normally we aren’t looking for exact pressures – rather we need to know the pressure differences between the high side and the low side of a system. To do this we use a few different types of gauges. © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

 The type of gauge used on a refrigeration service manifold gauge set is the Bourdon tube gauge. This is used for indicating system pressures. The gauge manifold is fitted with two gauges.  The pressure gauge (red) only measures high side system pressures above 0 kPa (atmospheric pressure).  The compound gauge (blue) measures low side system pressures above or below 0 kPa.  Most gauges with an indicating needle are Bourdon tube gauges. © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

 For measuring very small pressures of less than 1 kPa a manometer or a magnehelic gauge is used. This is used for measuring the pressure drop across air conditioning filters or duct pressures.  This is a digital manometer © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

 There are two types of monometer gauges we use at Fresh or Freezing. They are U tube monometers and inclined monometers.  U tube manometers are filled with mercury and are used for measuring pressure drops across water cooled condensers, chilled water and hot water coils and chillers (mmHg).  U tube manometers can also be filled with a coloured manometer fluid to measure static pressure differences across air handling systems (Pa).  Inclined manometers are filled with coloured manometer fluid and used to measure pressure drops of air across filters. They are also used to measure ductwork static pressures and velocity pressures to determine air flow rates (Pa). © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

 As part of our work we need to measure vacuums. In the field, vacuums are measured with electronic vacuum gauges. © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

 We also need to measure atmospheric pressure. To do this we use a barometer. © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

 All our equipment and tools have to be stored and maintained properly so they give us accurate readings. I always make sure they are clean and placed in their correct storage place when I’ve finished using them.  Generally Bourdon tube gauges are reasonably rugged and will require little in the way of regular maintenance. A periodic test for leaks is good practice.  Calibration usually consists of removing any residual refrigerant, in keeping with the current codes of good practice, then adjusting the needle of the gauge to read 0 kPa at atmospheric pressure. © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

 As gauges are usually fitted to a service manifold, maintenance includes replacing the rubber seals in the ends of the gauge lines, and giving the gauge lines a visual check to look for perishing of the lines, cracks in the outer covering of the lines, and any other signs of mechanical damage.  Keep gauge lines sealed to keep out dirt and other contaminants.  Other types of pressure gauges require specialised maintenance which must be carried out by suitably qualified persons. © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

 When taking readings, be careful. You will be working on an operating unit. You need to be aware of rotating machinery, as well as the fact that some components will be very hot or cold. The refrigerant in the gauge lines and the system may be at high pressure and can cause burns and damage the ozone layer if it escapes.  You need to be careful to avoid the gauge needles bouncing from the refrigerant oscillation, especially in the high side, as this will cause damage to the gauge mechanism. © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

 Remember:  The red gauge is fitted to the high side of the system as it is a pressure gauge, ie it only reads pressures above 0 kPa.  The blue gauge is fitted to the low side of the system as it is a compound gauge. It reads pressures above and below 0 kPa. © Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence