# Water pressure gauge

Figure 1: Water pressure gauge

A water pressure gauge is a pressure measurement instrument that indicates the water pressure in a system. It is a calibrated pressure indicator connected to a water pipe or tank and translates the force exerted on it into units such as Pascal, bar, Torr, etc. Water pressure gauges are invaluable devices in domestic, commercial, and industrial applications. They are easy to use, are durable, require little maintenance and are long-lasting. They are practical and provide an on-the-spot measurement of pressure, which is crucial information for various water applications.

The water pressure in a system can be static or dynamic. Static pressure is uniform in all directions, and it is the pressure in a water system that is not moving. Dynamic pressure is the additional pressure due to the flow direction of the fluid. Dynamic pressure has little impact on the surfaces parallel to the flow direction but helps measure flow rates and indicates a water system’s running pressure. Dynamic pressure is a form of differential pressure measurement. Water pressure gauges measure the “gauge pressure of a system. The gauge pressure is the absolute pressure minus atmospheric pressure, while the absolute pressure is zero-referenced against a perfect vacuum. The atmospheric pressure value within the area a water pressure gauge is installed will affect the “gauge pressure measurement. Learn more about pressure types.

## Bourdon tube operation

Figure 2: The Bourdon tube: inlet pipe (A), socket block (B), stationary end of the Bourdon tube (C), moving end of the Bourdon tube (D), pivot and pivot pin (E), sector gear (F), indicator needle (G)

Water pressure gauges have been used for over a hundred years. Therefore, there are multiple methods and mechanisms to measure water pressure. Each method has its advantages and disadvantages with different specifications of pressure range, sensitivity, and response speed. The most common water pressure gauge is the Bourdon gauge, which is covered in this article. There are other pressure gauge types like bellows, diaphragm, liquid filled pressure gauges, and digital pressure gauges, but they aren’t as common.

The Bourdon gauge is a mechanical device that measures and indicates the gauge pressure in a system. It uses the principle that when fluid pressure is applied to the inside of the tube, the tubes oval cross-section becomes more circular and this straightens the tube. Depending on the workability and the elastic range of the material, the cross-section change can be inconspicuous. This small change can be magnified by forming the tube in a helix or C-shape that tends to straighten or uncoil as the tube is pressurized. The tube then goes back to its normal position when fluid pressure disappears.

The water pressure gauge is connected to a water system, like a pipe, fluid enters the measurement device at the inlet pipe (A). The inlet pipe is held by the socket block (B), which also holds the device to the process line. The fluid pressure flows to the stationary end of the Bourdon tube (C). The pressure is transmitted across the C-shape to the moving end of the Bourdon tube (D). This pressure forces the C-shape to straighten. At the moving end of the Bourdon tube, a pivot and pivot pin (E) connects the straightening motion to the sector gear (F). The gearing system amplifies the motion at the moving end of the Bourdon tube such that a very little pressure change translates to a significant movement of the indicator needle (G). The indicator moves in a circular path, usually from left to right, over a calibrated scale.

## Selection criteria

There are several things to consider when choosing the correct water pressure gauge for your application. Below we take a look at the most critical parameters.

• Measuring range: Water pressure gauges are primarily selected based on the operating pressure range of the process. The range is defined from 0 to a maximum pressure (gauge pressure) and is displayed on the indicator scale. The selected measuring range partly defines the scale division. The scale division is the size of unit change that can be read from the indicator. When selecting a water pressure gauge, choose a maximum pressure that is closest and best fits your application. A pressure gauge with a maximum pressure range that is too high for an application will be inaccurate in measurement.
• Accuracy: Dependent on how critical precision measurement is to your application, check that the water pressure gauge accuracy is high enough to avoid wrong readings when small pressure changes are desired to be observed. Remember that your selection of measuring range indirectly affects accuracy. Read more about pressure measurement accuracy.
• Connection size, type, and location: There are different connection sizes for water pressure gauges. The dimensions are usually measured in inches. The connection size selection is essential when the pipe is relatively small or a holding socket for the water pressure gauge already exists. The connection type is more important than the size. It is quite common to have an outer thread cylindrical connection which allows easy replacement. The connection location can be below, above, or behind the gauge. Your application space requirements may affect the connection location.
• Maximum operating temperature: Most water pressure gauges work within the 60 – 80 C maximum temperature range. There are special water pressure gauges for high-temperature applications.
• Unit of measurement: There are different pressure measurement units (Pascal, bar, technical atmosphere, standard atmosphere, Torr, Psi). Most water pressure gauges have two units on the indicator. Check to ensure you select the version with the unit you are most comfortable with.
• IP protection: The IP code is important, especially if you will use the water pressure gauge in an environment with dust, condensation, or water splashes. Higher IP ratings will mean a higher cost of the gauge as well.
• Digital reading: There is an option to have a digital display of the measured water pressure. Consider if this fits your need, and remember it will need to be powered. However, most water pressure gauges have a dial indicator and do not require external power to operate.

## Applications

Figure 3: A pressure gauge for a sprinkler system

1. Pool filter pressure gauge: A pool filter pressure gauge helps keep track of the pressure variations within a pool system. After a baseline pressure reading, high pressure typically indicates the filter needs cleaning, and low pressure indicates a flow issue. Learn more about pool filter pressure gauges
2. Irrigation and sprinkler system: Water pressure gauges are used to indicate the pressure in an irrigation network in a farm or a sprinkler system in the garden.
3. Detection of leakages: Water pressure gauges are installed in closed water loops, such as a heating circuit or a process line, to indicate a leak in the circuit.
4. Measuring tank volume with pressure: A pressure gauge can help track the water volume in an open vertical tank or column of water. Changes in the pressure will indicate discharge or refill of water from or to the tank.
5. Well pressure: Houses that are supplied with fresh water from the well use water pressure gauges to know when there is low well pressure. This helps to plan for other sources of water or to drill another well.

With all applications pressure gauges are subject to the usual wear and tear, read our article on the maintenance and troubleshooting of pressure gauges