An open-end mercury manometer is connected to a low pressurepipeline that suppli

Question

An open-end mercury manometer is connected to a low pressurepipeline that supplies a gas to a laboratory. Because paint was spilled on the arm connected to the line during a laboratory renovation, it is impossible to see the level of the manometerfluid in this arm. During a period when the gas supply is connectedto the line but there is no gas flow, a bourdon guage connected tothe line downstream from the manometer gives a reading of 7.5 psig.The level of mercury in the open arm is 900mm above the lowest part of the manometer. a) When the gas is not flowing, the pressure is the same everywhere in the pipe. How high above the bottom of the manometer would the mercury be in the arm connected to the pipe? b) When gas is flowing, the mercury level in the visibile arm drops 25 mm. What is the gas pressure (psig) at this moment?

Explanation / Answer

7.5 Psig correspond to 7.5+14.7 Psia =22.2 Psia

14.7 Psia =760 mm Hg

22.2 Psia =22.2*760/14.7=1147.755 mm Hg This ithe pressure of the gas when there is no flow. So 1147.755-900= 247.755mm Hg is above the bottom of the manometer would the mercury be in the arm connected to the pipe

The pressure drop is 25mm Hg= (25/760)*14.7 Psia.=0.483 Psia

The gas pressure is 22.2+0.483=22.683 Psia

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