### Pressure Measurement

• Apply the principles of manometer to calculate pressure.

• Differentiate between absolute pressure and gauge pressure.

### Solved Example:

#### 61-2-01

Differential manometer is used to measure: (Based on JKSSB JE CE Oct 2021-Shift I)

### Solved Example:

#### 61-2-02

Pitot tube is used for measurement of: (ISRO RAC 2017)

### Solved Example:

#### 61-2-03

1 bar pressure is nearly equal to:

Solution:
1 bar = 1 $\times$ 10$^5$ N/m$^2$ $750\ mm\ Hg = 750 \times 10^{-3} \times 13600 \times 9.81 = 100062\ N/m^2$

### Solved Example:

#### 61-2-04

Mercury is often used in barometer because: (Gujrat Engg Services 2017- Civil Part II)

Solution:

Mercury is much heavier than water (13.6 times) hence the column height required is only 760 mm as compared to 10.33m of water column. Also, it has very less vapor pressure hence the reading will be accurate. Mercury has in fact less viscosity, hence it is faster to react to the changes in pressure.

### Solved Example:

#### 61-2-05

Barometer is used to measure: (CTET Sept 2014- Paper II)

Solution:
Barometer is used to measure atmospheric pressure. To measure difference of pressure between two points, U-tube manometer is used.

### Solved Example:

#### 61-2-06

Select the correct statement:

### Solved Example:

#### 61-2-07

Which of the following is correct?

Solution:
Absolute pressure is measured with reference to perfect vacuum, whereas gauge pressure is measured with reference to atmospheric pressure. Hence the difference between absolute pressure and gauge pressure is equal to atmospheric pressure.

### Solved Example:

#### 61-2-08

The pressure in Pascals at a depth of 1 m below the free surface of a body of water will be equal to:

Solution:
$P = h \rho g = 1 \times 1000 \times 9.81 = 9810\ Pa$

### Solved Example:

#### 61-2-09

The absolute pressure exerted on a diver at 30 m below the free surface of the sea will be :(Take barometric pressure = 101 kPa, specific weight of seawater = 10.3 $kN/m^3$

Solution:
$P = P_{atm} + h\rho g = 101 \times 10^3 + 30 \times 10.3\times 10^3 =\ 410\ kPa$

### Solved Example:

#### 61-2-10

One of the differences between absolute pressure and gauge pressure is: (Prof. Prashant More's notes of Fluid Mechanics-II)

Solution:
Let us study these options individually.
Option A: Difference between gauge pressure and absolute pressure is the atmospheric pressure.
Option B: Absolute pressure can be positive or negative but gauge pressure can be positive or negative.
Option D: Gauge pressure is measured from atmospheric pressure whereas absolute pressure is measured from perfect vacuum.

A lake has maximum depth of 60 m. If the mean atmospheric pressure in the lake region is 91 kPa and the unit weight of the lake water is 9790 $N/m^3$, the absolute pressure (in kPa, round off to two decimal places) at the maximum depth of the lake is: (GATE Civil 2021)