The manometer (from the Greek μανός, light and μέτρον, measurement) is a measuring instrument for the pressure of fluids contained in closed containers. Two types of manometers are distinguished, depending on whether they are used to measure the pressure of liquids or gases.[1]​.

Contenido

Muchos de los aparatos empleados para la medida de presiones utilizan la presión atmosférica como nivel de referencia y miden la diferencia entre la presión real o absoluta y la presión atmosférica, llamándose a este valor presión manométrica; dichos aparatos reciben el nombre de manómetros y funcionan según los mismos principios en que se fundamentan los barómetros de mercurio "Mercurio (elemento)") y los aneroides. La presión manométrica se expresa ya sea por encima, o bien por debajo de la presión atmosférica. Los aparatos que sirven exclusivamente para medir presiones inferiores a la atmosférica, o negativas, se llaman vacuómetros. También manómetros de vacío.

Two open branch pressure gauge

These are the elements with which positive pressure is measured, these can adopt different scales.

The simplest manometer consists of a U bent glass tube containing an appropriate liquid (mercury, water, oil, among others). One of the branches of the tube is open to the atmosphere; the other is connected to the tank that contains the fluid whose pressure is to be measured (Figure 1). The fluid from the container penetrates part of the tube at ∪, making contact with the liquid column. The fluids reach a configuration of

equilibrium from which it is easy to deduce the absolute pressure in the tank:

it turns out:.

where:.

If the density of said fluid is much lower than that of the manometric liquid, in most cases the term ρgd can be neglected, and we have:.

so that the manometric pressure p-p is proportional to the difference in heights that the manometric liquid reaches in the two branches. Obviously, the manometer will be more sensitive the lower the density of the manometric liquid used.