1. Simple U-TUBE Manometer
It is a manometer that has a fluid reservoir and the end open to atmosphere. It is common to have two different type of fluids within the manometer, one fluid in the reservoir, and another type of fluid within the U.
Example 1
A U-tube manometer similar to that shown in below is used to measure the gauge pressure of water (mass density ρ = 1000 kg /m3). If the density of mercury is 13.6 × 103kg /m3, what will be the gauge pressure at A if h1 = 0.45 m and D is 0.7 m above BC.
Water
Mercury, Hg

2. Solution : Considering the pressure at left-hand limb;
PB = Pressure, at A + Pressure due to depth, of fluid P

3. Example 2.5
A U-tube manometer similar to that shown below is used to measure the gauge pressure of a fluid P of density ρ = 1000 kg/m3. If the density of the liquid Q is 13.6 × 103kg/m3, what will be the gauge pressure at A if h1 = 0.15 m and h2 = 0.25 m above BC. Take into consideration patm = kN/m2.

4. Solution ,
Since

5. Activity
The U-tube manometer measures the pressure of water at A which is below the atmospheric pressure. If the specific weight of mercury is 13.6 times that of water and the atmospheric pressure is kN/m2, find what is the absolute pressure at A when h1 = 10 cm, h2 = 25 cm and the specific weight of water is 9.81×103N/m3.

6. Solution

7. Self assessment
2.3 Assuming that the atmospheric pressure is kN/m2 find the absolute pressure at A in the figure below when
a) Fluid P is water, fluid Q is mercury ω = 13.6, a = 1 m and h = 0.4 m.
b) Fluid P is oil ω = 0.82, fluid Q is brine ω = 1.10, a = 20 cm and h = 55 cm.