An inverted U-tube manometer is used to measure the relative pressure between tw

Question

An inverted U-tube manometer is used to measure the relative pressure between two different pipes indicated by A and B (note only the cross-sectional view of the pipes is shown). Assume that the pressure PA in the pipe A and pressure PB in pipe B is uniform and is maintained constant. The process fluid in both pipes (gray shaded region) indicates a liquid with specific gravity of 2.6 (reference is water with density of 1 gm/mL).  

The manometer has a light liquid (clear region) with a specific gravity of 0.8 at the top. The heights shown in units of cm are h = 62, a = 74, and b = 37, choose the correct answer below.

A) The pressure at B is lower than at A

B) The magnitude of the pressure difference is 0.312 atm

C) The magnitude of pressure difference is 11.1 ft of H2O

D) Two choices, A and B are correct

E) Two choices, A and C are correct

F) Two choices, B and C are correct

G) None of the A, B, or C choices are correct

Explanation / Answer

The magnitude of pressure difference b/w A & B can be calculated as below:

PAB = 2600 x g x a + (2600-800) x g x h

= 2600 x 9.81 x 0.74 + (2600-800) x 9.81 x 0.62

= 29812.216 Pa

= 0.294 atm = 9.9737 ft H2O

Point B is at a higher pressure. Pressure in atm is close to option B, yet incorrect. So I would suggest option (G).

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