Manometre

A manometer, also called a manomètre in French, is a device used to measure pressure by balancing it against a column of liquid. The basic principle is hydrostatic: the pressure at a given depth in a fluid is proportional to the fluid’s density and the height of the column, P = ρ g h. The pressure being measured is indicated by the resulting height difference in the manometer fluid.

There are several configurations. U-tube and single-column manometers use a liquid column, often mercury or water, whose height difference corresponds to pressure. Inclined manometers improve sensitivity for small pressures. Bourdon-tube and other elastic-element manometers convert pressure into mechanical displacement and may be read directly or via an attached sensor. Diaphragm and bellows manometers use a flexible element that deforms under pressure. Digital manometers employ electronic sensors to convert pressure into a digital reading.

Manometers can measure gauge pressure (relative to atmospheric pressure), absolute pressure (relative to a vacuum), or differential pressure between two points. Readings are expressed in units such as pascals (Pa), kilopascals (kPa), bar, psi, or Torr. The choice of fluid affects response time, temperature sensitivity, and safety; mercury provides high density but is toxic, so alternative fluids like water or silicone oil are common for lower pressures.

Maintenance involves keeping the device vertical for accuracy, removing air bubbles, and calibrating against known references. They are widely used in laboratories, HVAC and process industries to monitor pipelines and processes, in educational settings for demonstrations, and in some medical contexts for approximating blood pressure readings. Differential manometers measure the pressure difference between two points, while open-ended devices measure pressure relative to ambient.