The Whats and Hows of Manometers

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Differential digital presure manometer in use

The manometers of today are handy tools with many industrial applications. People often use them to measure the pressure difference between two points of a pipe, or in other cases, to measure the pressure difference between two pipes. This device measures pressure using the relation between the pressure and the head. It can measure both high and negative pressures, but it can also measure differential pressure.

Characteristics of a Manometer

  • This device measures the pressure of fluids. It has a tube that is bent and contains more than one liquid with different densities;
  • To do the measurement, you need to place the liquid with the known pressure at one end and the liquid with the unknown pressure at the other;
  • The differential pressure manometer can only tell you the difference between the two pressures;
  • The manometer also measures static pressure.
Front view of Digital Manometer Air Pressure Meter shown measures on display
source: alitools.io

How Does a Manometer Work?

This device functions based on a hydrostatic balance principle. It often contains a reservoir with liquid. You need to connect the reservoir to the source to measure the pressure. The column that you will connect it with is exposed to atmospheric pressure. These columns are either sealed or unsealed. If you need to measure gauge pressure, you should use an open column manometer. Those with a sealed column are used to measure absolute pressure and vacuum.

When you connect the device to the source, there will be variations in the liquid levels inside the column. These variations depend on the pressure source that you’re measuring. This is why you should always know the type of liquid you are measuring. Depending on its type, there can be a rise or fall in the pressure. You should also know the specific gravity to do the measurement properly.

Digital manometer in use
source: nerdtechy.com

Types of Manometers

Manometers are classified into two different types – simple and differential.

Differential Manometers

The differential digital manometer is the most common type, and it’s much more convenient than the simple one. It measures the difference in pressure between two points. It can be classified into two groups – U-tube and inverted U-tube. The former contains a U-shaped glass. One end remains open to the atmosphere, while the other is connected to the point where you need to measure pressure. This device is ideal for when you need to measure large pressures in lighter liquids. Its tube is filled with mercury, which can be considered as a manometric fluid, and you can use it to measure either gas or liquid.

Differential Digital Manometer With USB Interface In Use
source: joom.com

The U-tube manometers are commonly used in laboratories. They’re ideal for low range pressure measurement and can detect the pressure drop in valves.

The other type of differential manometers has an inverted U-tube instead, and it’s common in measuring the difference of low pressure. In this case, you need to connect both ends of the tube to the point where the pressure difference is determined.

Simple Manometers

These manometers measure the fluid pressure at a point in the pipe. They are classified into three types – piezometer, U-tube and single column manometer. The piezometer has a vertical tube, and it operates on the hydrostatic equilibrium principle. One end is open to the atmosphere, while the other is connected to the point where you measure the pressure. However, this device comes with several disadvantages. It can only measure gauge pressure and can’t measure the negative pressure or the gas pressure.

Simple Manometer U-tube
source: britannica.com

What Are the Advantages of Using a Digital Manometer?

  • An electronic manometer has good accuracy and sensitivity;
  • It requires less maintenance;
  • It doesn’t vibrate;
  • It’s easy to use;
  • It can even measure extremely low pressures;
  • You can change its sensitivity according to your needs.

Applications

  • You can use a manometer for pressure monitoring applications;
  • It can monitor the air and gas pressure in compressors;
  • You can use it to measure static pressure and vacuum;
  • They’re helpful in power plants, research labs, gas analysis, weather studies, etc.
Digital Manometer with LCD Display in a box
source: bahamas.desertcart.com

Tips to Accurately Measure Pressure with a Manometer

  • Install new batteries. If you’re looking to get true readings, installing new batteries is a good practice before making pressure readings. Even new manometers sometimes give inaccurate readings if their batteries aren’t up to the mark.
  • Mandatory zero adjustments. To keep any potential errors and discrepancies at bay, use the restore toggle which brings the display back to null.
  • Measurement of static pressure. When the display shows positive pressure, this implies that the pressure is more than that of the atmosphere, while a negative pressure means that it’s below the atmospheric pressure.
  • Use of backlight feature. Sometimes you need to do pressure readings in dark environments or in poor illumination. To view the readings in these conditions, make sure that you’re using a manometer with a backlight feature. This feature lights up your manometer’s screen for two minutes before turning it off to conserve the battery.
  • Use of memory feature. Often, when you do pressure readings, you will need to record several of them to review them later or observe a specific pattern. Modern electronic manometers have a built-in memory that stores multiple pressure recordings. You can see the number of saved recordings on the device’s display.