Manometer and Bourdon Gage  The elevation of the horizontal pipe is slightly above sea level. Water flows through the pipe and it has been fitted with a manometer and also a Bourdon gage. Calculate the pressure of flowing water through the pipe according to the manometer then according to the bourdon gage.

♦  i) Start where the pressure is known.

• The pressure outside, in the atmosphere, precisely at the level of the pipe center-line. is one atmosphere.
• The path now moves upward to the uppersurface of the mercury. Follow a hydrostatic path from the atmosphere through the gage to the center-line of the flow of water.

  p_atm + 13,600kg/m³9.81m/s²(0.284m) -1,000kg/m³9.81m/s²(0.142m) = 137.8 kPa

♦  ii) The Bourdon Gage is connected to the side of the pipe at its celnter-line. Thus atmospheric pressure plus the gage reading (G.R.) will equal the water pressure.

p_atm + G.R. = p_water   or         101.3kPa + 38kPa = 139kPa

One pascal difference is quite small. The bourdon gage might be incorrect - it had to be calibrated. The water pressure should decrease in the direction of flow.