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.
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.
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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.
Read our selection tips for pressure gauges to learn more about this subject.
Figure 3: A pressure gauge for a sprinkler system
With all applications pressure gauges are subject to the usual wear and tear, read our article on the maintenance and troubleshooting of pressure gauges.