A pressure gauge is an instrument used to measure the point pressure of a gas or liquid enclosed in a vessel, or flowing through a closed pipe or channel. Pressure gauges are widely used in industry and in everyday life to check the pressure of compressed gases or gases stored in tanks. They are usually made with U-shaped glass tubes and have a liquid inside, which is pushed by the pressure of the gas or fluid to be measured, creating a difference in height, which shows the pressure of the gas we are analysing. In this article we will see how to make a homemade manometer with everyday and easily available materials.
- A small plastic bottle with a lid.
- A balloon.
- Straws or thin plastic tubes of different sizes.
- Coloured water.
- Silicone sealant.
- Adhesive tape.
- Small rubber stopper with a hole in the middle (as used in laboratories).
- Tape measure.
Pressure gauge mounting
To build our pressure gaugeTo do this, start by making two holes in the lid of the bottle, so that the straws or thin plastic tubes can fit through the holes. We use a long straw or a long thin plastic tube that reaches almost to the bottom of the bottle and protrudes approximately 40 cm from the lid.
In the other hole we place a flexible straw. Once both straws are in place, we seal the lid with silicone, top and bottom, so that when we close the bottle it is hermetically sealed. After sealing the lid, fill the bottle with coloured water up to a height below the middle of the bottle and place the lid that we have previously sealed with the straws.
Next, we place a straw or plastic tube with a slightly larger diameter at the end of the flexible straw, to complete the assembly of our pressure gauge.
Now, we mark or measure with a tape measure the height of the coloured water inside the large straw, writing it down in a notebook. Then, we place the rubber cap on the mouth of the balloon (using adhesive tape to avoid air leaks), fill the balloon with air, cover it with a finger and place the free end of the straw or plastic tube in the balloon, and we will see how high the coloured water rises in the large straw. We mark the height and we will have our measure of the height of the balloon. pressure.
How it works
The pressure is defined as the force exerted by a column of fluid over a given area. Manometric measurements are a consequence of the force exerted by the fluid (gas or liquid) on a liquid of known specific gravity (the coloured water). This will create a height difference (final height of the water column - initial height of the water column) which when multiplied by the specific gravity of the liquid, or by a factor given by the acceleration of gravity and by the density of the liquid, will give the relative pressure of the gas inside the balloon. The equation to calculate this pressure is as follows:
P = ρxgxΔh
P: Pressure (Pa)
ρ: is the density of water (Kg/m3 ).3).
g: Acceleration of gravity (m/s2).
Δh: Height difference or height of the water column (m).