How Liquid Pressure Measured Using Piezometer

piezometer

What is Piezometer?

Piezometer is the simplest form of liquid pressure measuring device. It measures the gauge pressure of liquid in a system by measuring the height up to which the column of liquid rise against the gravity. Measured liquid column height is known as piezometric height.

Piezometer is a glass tube, one end of it is connected to the point where the pressure to be measured and other end is open in atmosphere. The height of liquid column is read manually, in some cases, electrical transducers are used to read it automatically and making the data recording more convenient.

Piezometer - Equation to find pressure

Piezometer gives the pressure head at a point. Consider the liquid of density ρ give a pressure head of h at a point, then the pressure at a point is

P= ρgh
Here g is acceleration due to gravity

Advantages, application and disadvantages of Piezometer

Advantages and application
  • Simple and reliable
  • Used to measure static pressure fluid in a container.
  • One of the main application of piezometer is that it is used to measure pore water pressure/ ground water level.
  • They are helpful in calculations to find performance of soil and rock.

What are the limitations of Piezometer?
  • Piezometer cannot used to measure the static pressure of gas because gas do not form form a free surface.
  • Piezometer not suitable(but it can be used)to measure the vacuum pressure, because vacuum pressure cause suction of air into the container/ vessel . It convenient only when static pressure of liquid is greater than the atmospheric pressure (gauge pressure)
  • Piezometer are not suitable to measure large pressure of lighter liquid, because for this condition piezometric head is very high. It would require long glass tube, which are difficult to handle.

What is the difference between a piezometer and Pitot Tube?

The construction of piezometer similar to the pitot tube. But piezometer specifically designed to measure static pressures, while the pitot tube designed to measure fluid flow.



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