1. The problem statement, all variables and given/known data Determine the flow rate, Q. Ignore energy losses. Given: D1 = 100 mm D2 = 75 mm Fluid in the pipe is water. Fluid in the metre is mercury. S.G. of Mercury is ~13.6. The difference in height of the mecury columns is 80mm. Diagram is below. 2. Relevant equations Bernoulli's Equation. Equation of Continuity. (Q1 = Q2) 3. The attempt at a solution I approached this as a manometer question, but with that orifice in the flow I was unsure on how to proceed. I chose a datum as the lower of the two levels of mercury. The expressions I got were: Px-x = Pressure due to the flow + Pressure due to the height of the water above the mercury + the pressure due to the mercury above the datum. This was for the left hand side. Px-x = P1 + ρwgh + ρmgh', where h' = 80 mm and h is an unknown height which cancels out when the left side and right side are equated. For the right hand side I said Px-x = Pressure due to the flow + Pressure due to the height of the water. Px-x = P2 + ρwg(h+h') For this second equation I feel there is something missing, surely that opening in the flow causes an additional term to be added?