Many fluid and piping systems operate at a set pressure to ensure optimal performance. A hydraulic gauge is used to measure the pressure in a fluid system, to ensure that there are no leaks or pressure changes that could adversely impact performance of the system. Hydraulic gauges are often used in oil, fuel, and water systems that use pumps and compressors, and operate at elevated pressures. It measures pressure relative to the surrounding atmospheric pressure, also referred to as ambient pressure.
A common type of hydraulic gauge is known as the Bourdon gauge. It uses a curved internal tube that changes shape when fluid pressure is applied. The tube is mechanically attached to a hand on the dial of the gauge using a mechanical linkage. As the curved shape of the tube changes, the tube will move and cause the hand to rotate to a position on the dial that corresponds to the pressure in the system. Hydraulic pressure is often measured in pounds per square inch (psi) or as a depth of fluid, expressed as inches of water or mercury.
Hydraulic gauges are manufactured for different pressure ranges and types of fluid. The gauge selected for specific application must be designed to withstand the operating pressure, and to be compatible with the fluids used in the system. For fluids that are highly corrosive or that operate at high pressures, materials like titanium, metal alloys, and chemically-resistant plastics are often used to ensure gauge performance and that useable life is maximized.
A hydraulic gauge is most often permanently installed, and used for continuous measurement and monitoring of pressure. These gauges can also be purchased as portable handheld units. Hydraulic gauges are available in a wide range of quality levels and with many operating features. A basic gauge provides a simple analog dial for reading pressure and is typically fabricated using steel and brass components. More expensive gauges generally provide a digital readout, have permanently sealed internal components, use better quality materials, and provide a higher level of accuracy.
After a pre-determined period of use, a hydraulic gauge may need to be removed from service and re-calibrated. The calibration process is completed using a test gauge in combination with a device that applies a known fluid pressure to the gauge being tested. The test gauge is extremely sensitive and accurate, and is used to determine if the gauge being calibrated is measuring the correct pressure or if it requires re-calibration or repair.