Mechanical Properties of Fluids

What Is a Manometer?


A manometer is a device that we use to measure the pressure of the pipelines (cab be of gas, water, liquid, etc.) Also, it is usually referred to as a U-shaped tube that is filled with a liquid. In this topic, we will discuss what is it and how it works.

What is Manometer?

It refers to a device or gauge that measure pressure in lines. Furthermore, the pressure can be of anything means it can be of liquid, gas, steam, etc.  Besides, you can easily make it as part of your laboratory experiment to reveal the pressure of air on a liquid column.


How to Build a Manometer?

We can make a simple manometer by filling a clear plastic tube partially with a color liquid. So, that it the level of fluid can be easily observed. Furthermore, bent the tube in U-shape and fix it in an upright position.

Also, make sure that the level of fluid in two vertical columns is equal at this point. Most noteworthy, the pressure on these two vertical columns is equal at this point because they are exposed to the same pressure. In addition, this level is marked as the zero points of the manometer.

Pressure Measurement

We place it against a measuring scale to allow any difference in the height of the two columns. Furthermore, we can use this height differential directly to make a relative comparison between different test pressures. Besides, we can use this type of manometer to calculate it when we know the density of the liquid.

How Does a Manometer Work?

In the manometer, one end connects to a gas-tight seal to test the pressure source. In addition, the other end of the tube is left open to the atmosphere and it will be subjected to the pressure of approximately 1 atmosphere (atm).

Besides, the test pressure is greater than the pressure of 1 atm (atmosphere) the liquid in the column will be forced down by the pressure. Furthermore, it will cause the liquid of the reference column to rise by an equal amount.

Calculation of the Pressure

The pressure applied by a column of liquid is given by the equation P = hgd. In this equation, P is the calculated pressure, h is the fluids heights, g is the gravitational force and d is the density of the liquid.

Also, it is measuring a differential pressure rather than absolute pressure. Furthermore, we use the substitution P = Pa – Po. Besides, in this situation Pa is the test pressure and P0 is the reference pressure.

Use of Manometer (Example)

Suppose that the fluid in it is mercury and the height of the referenced column is 0.02 meters that are higher than the pressure of fluid in the test column. In addition, use 13,534 kg/ m3 (Kilogram per cubic meter) as the density of mercury and acceleration of the gravity as 9.8 m/s2 (meter per second squared).

The calculation of pressure differential in two column as hgp = 0.02 × 9.8 × 13,534 = approximately 2,653 kgkg•m-1•s-2. Furthermore, you can use Pascal for the unit of pressure, with approximately 1,01,325 Pascals equal to 1 atm of pressure. Therefore, the pressure differentiation in manometer is Pa – P0 = 2,653 / 1,01,325 = 0.026 atm.

Besides, the pressure in the test column (Pa) is equal to P0 + 0.026 atm = 1 + 0.026 = 1.026 atm.

Solved Question for You

Question. Which of the following a manometer cannot measure?

A. Solid

B. Liquid

C. Gas

D. Fluid

Answer. The correct answer is potion A. As liquid, fluid, and gas can be measured with a manometer.

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