What is a Manometer?

Types and Applications of Manometers

One of the devices used for pressure measurement is the manometer. In fact, a manometer is a pressure gauge used to measure the pressure of gas confined in a container. The most important component for pressure measurement is the Bourdon tube. The Bourdon tube is one of the main parts of a manometer, made in a C-shape with an approximately oval cross-section, one end sealed and the other connected to the pressure point. Bourdon-type pressure gauges can measure pressures from 30 to 50,000 psi. The applied pressure causes the free end of the Bourdon tube to move, and this movement is transmitted through a lever system to a gear and pointer, which indicates the pressure on the dial.

The Bourdon tube consists of a curved metal tube with an oval cross-section that tends to straighten as the fluid pressure increases and curves more as the pressure decreases. Changes in curvature are transmitted to the pointer through a gear system. The direction and amount of pointer movement depend on the direction and magnitude of the tube's curvature change. Bourdon pressure gauges are used to measure pressures both above and below atmospheric pressure.
A U-tube manometer can be used to measure pressure, vacuum, or the pressure difference between two points. This method is one of the simplest yet most accurate ways to measure pressure. It is usually employed in cases where the operator needs to observe the pressure locally.

Types of Pressure Gauges Based on Pressure Type

Pressure sensors can be classified based on their measurement range, operating temperature range, and most importantly, the type of pressure being measured. According to the type of pressure, pressure gauges are divided into five categories:

Absolute Pressure Sensor

This sensor measures the pressure of a point relative to a perfect vacuum (0 psi). Atmospheric pressure at sea level is 101.325 kPa (or 14.7 psi) relative to a vacuum.

Gauge Pressure Sensor 

This sensor is used in various applications because it can be calibrated to measure the pressure of a point relative to atmospheric pressure at another point. A tire pressure gauge is an example of a gauge pressure indicator. When the tire pressure gauge reads 0 psi, the pressure inside the tire is actually 14.7 psi, which equals atmospheric pressure.

Vacuum Pressure Sensor

This sensor is used to measure pressures below atmospheric pressure at a specific point. The reference for vacuum sensors varies in industry, which can cause confusion; it may refer to pressure relative to atmospheric pressure (as in negative gauge pressure measurement) or pressure relative to a vacuum.

Differential Pressure Sensor

This sensor measures the difference between the pressures at two or more points that are introduced as inputs. For example, it can be used to measure the pressure drop across an oil filter. Differential pressure is also used for measuring flow rate or liquid level in tanks.

Sealed Pressure Sensor

This sensor is similar to a gauge pressure sensor, except that it is pre-calibrated by the manufacturer to measure pressure relative to sea-level pressure.

Applications of Manometers
Pressure Measurement

This is the primary application of pressure sensors, used in areas such as meteorological equipment, airplanes, automobiles, and other devices where pressure is a critical parameter.

Altitude Measurement

Its application is in airplanes, rockets, satellites, weather balloons, and similar devices. In all these cases, the relationship between pressure changes and altitude relative to sea level is used.

Flow Measurement

Flow can be measured using the Venturi effect and its relationship with pressure. The pressure difference between two sections of a Venturi tube (with different diameters) is measured. This pressure difference is directly related to the flow velocity through the tube. Since the pressure difference is relatively small, a low-range pressure sensor is used.

 
Level / Depth Measurement

A pressure sensor can be used to measure the liquid level. This technique is commonly applied to determine the position of a submerged object in water (such as divers or submarines) or the liquid level inside a tank (such as the liquid in a water tower).

Leak Testing

Leakage in a system can be determined by measuring the pressure drop. The common methods for this purpose are:
1) Comparing the system pressure with the pressure of a system with a known leak and using this pressure difference.
2) Measuring the pressure and monitoring its changes over a period of time.