And in aviation, using pitot tubes, a differential pressure gauge measures airspeed in knots or miles.įour Applications for Differential Pressure Measurementĭifferential pressure measurement goes beyond regular pressure measuring. In flow applications, differential pressure gauges often read in SCFM (standard cubic feet per minute), GPM (gallons per minute), m³/s (cubic meters per second), etc. If measuring content in liquid level applications, users can choose among scales that read in pounds, kilograms, or gallons. There are also many options for units of measurement other than just psi, bar, and inches of water column. For filter applications, in-line connections (also known as end connections) are typical, and to measure the low pressure in air handling systems, a hose barb connection is the one most often used. For liquid level measurements, a combined top/bottom connection (total of four pressure ports) in combination with a ¼” NPT female thread can be the norm. Differential applications often require different pressure port positions, additional pressure ports, and different process connections than the typical ¼” or ½” NPT male thread used on standard gauges. The working pressure in almost every DP application is significantly higher than the actual DP range. Without knowing the working pressure, we cannot determine the correct DP gauge for the application. Besides the differential pressure range, the maximum working pressure is very critical. Even at very low differential pressure ranges, the DP gauge must be rugged enough to withstand very high working pressures. The range of a differential pressure gauge can go as low as 0.2″ H 2O for air handling systems and as high as 15,000 psi with a Bourdon tube DP gauge. A differential pressure gauge indicates only the Δp it basically eliminates all the unnecessary “noise.” Both pointers might indicate 100 psi, but a DP gauge would be sensitive enough to pick up a difference of as low as 10″ H 2O (inches water column), or 0.36 psi. As an example, let’s put two standard gauges on either side of a filter. Differential pressure gauges are designed to detect minute differences that the human eye cannot see. In the example, Δp = p1 – p2.īut why even use a differential pressure (DP) gauge? Why not just place a standard pressure gauge at the p1 and p2 measurement locations, and then have a technician work out the difference? Besides the extra time and effort required for manual calculations, a DP gauge is superior for several reasons: Differential pressure – the third method of measuring pressure – is simply the difference between two applied pressures, often referred to as delta p (Δp).
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