# How to Interpret Manometer Readings? Trouble-free Ways Given Here

A manometer is used for measuring differential pressure. It's just a scale. To interpret a manometer's readings, you multiply the reading obtained on the scale by the calibration factor. This ScienceStruck post explains how to read a manometer along with some examples.

Neha Gohad

Last Updated: Oct 04, 2018

Testing Room Pressure With a Manometer

- Close all the windows and doors to the room. Switch off the fans if any.
- Insert the end of the hose of the manometer underneath the door. Connect the other end to the manometer.
- Interpret the results according to the rise in water column. The room should maintain a slightly positive pressure of approximately 0.02 inch per water column.

How to Read a Manometer

● The pressure to be measured in Pascal can be obtained as follows:

**Pressure in N/m**

^{2}= ρ X g X hwhere,

**ρ**= density of liquid in kg/m

^{3}

**g**= acceleration due to gravity given by 9.8 m/s

^{2}

**h**= doubled height difference in meter.

How to Read a Mercury Manometer

● As mentioned earlier, measure the pressure in water inches.

● Specific gravity (SG) of a liquid is the ratio of the density of a substance to the density of water. The specific gravity of mercury is 13.6, which means it is 13.6 times denser than water.

● Specific gravity (SG) of a liquid is the ratio of the density of a substance to the density of water. The specific gravity of mercury is 13.6, which means it is 13.6 times denser than water.

● Gas pressure is given in millimeter ( an inch is 25.4 mm).

Numerical Example

A U-tube manometer filled with mercury is connected between two points in a pipeline. If the manometer reading is 26 mm of Hg, calculate the pressure difference between the points when water is flowing through the pipe. Density of mercury = 13.6 gm/cc, density of water = 1 gm/cc.

**Data:**Manometer reading (h) = 26 mm Hg = 0.026 m Hg

Density of mercury (ρ

_{m}) = 13.6 gm/cc

Density of water = 1 gm/cc

**Formula:**

For simple U - tube manometer,

**p**

_{1}- p_{2}= Δ p = (ρ_{m}- ρ)gh**Calculations:**

Water flowing through the pipe:

**Δ p = (ρ**

= (13600 - 1000) X 9.812 X 0.026

= 3214.4 N/m

_{m}-ρ)gh= (13600 - 1000) X 9.812 X 0.026

= 3214.4 N/m

^{2}