Column manometers
This are the elements which we measure the positive, negative and differential pressure. They can have different ranges. The simplest manometer consists in a glass tube folded in U, containing liquid (mercury, water, and oil amongst others). A branch of the pipe is open to the atmosphere (or to the second pressure output in case of differential pressure measurement), the other is connected to the tank containing the fluid whose pressure is going to be measured. The fluid of the tank moves through the U until reaching an equilibrium that we can measure through a graduated scale.
The version with only one branch has a small tank in the upper side that stores the liquid, performing the same function as the second branch of the U tube.
The scale is built by the density of the fluid (1 in the case of water).
For low pressures, there is the “inclined tube manometer” version. The inclination causes that a small increase in the pressure, the bigger is the movement through the tube.
Duplex manometer
It is the integration of two tubes and two Bourdon measuring needles in a single sphere and box. It allows direct comparison of the two pressures.
Manometers for special applications
They are suitable for specific applications such as equipment for nuclear industry, degreased for oxygen service, for absolute pressure manometers, etc.