Pressure gauge – keeping an eye on internal pressure

A pressure gauge is a testing and measuring device for hydraulic and pneumatic systems. There are manual and digital pressure gauges, which can be installed either permanently or as removable units.

Why a pressure gauge is necessary in hydraulics

Monitoring internal pressure is very important in hydraulic systems. Since liquids are incompressible, the pressure in hydraulic systems is theoretically the same everywhere.

However, valves, hoses, pressure reducers and other installations can cause significant fluctuations in internal pressure. In addition, faults in the hydraulic pump, its drive, or contamination in the oil can also lead to pressure fluctuations.

Temperature differences are particularly critical. At low temperatures, the oil becomes very viscous. Depending on the location within the hydraulic system, this can cause blockages. The opposite occurs when the oil overheats: the hotter the oil becomes, the thinner it gets. If it is also contaminated with water, the oil may even begin to boil. The resulting gas inclusions are compressible, putting the functionality of the entire system at risk.

To monitor internal pressure in the hydraulic system as comprehensively as possible, a number of inspection points are required. Pressure gauges are the standard fittings used for this purpose. Their greatest advantage is their simple, and therefore cost-effective, design.

How a hydraulic pressure gauge works

A pressure gauge consists of four components:

• Housing
• Connection
• Curved pressure tube
• Movement with dial

The pressure gauge connection consists of a hollow bolt with a standard thread. It is connected at defined points in the hydraulic system. The internal pressure is transmitted through the bolt into a curved pressure tube inside the housing. This pressure then attempts to force the curved tube apart. The tube’s movement is transmitted to the dial via a movement. The internal tube is typically made of brass, making it corrosion-resistant and durable.

In hydraulics, pressure gauges are also usually filled with oil or glycerin. This slightly dampens the needle movement and also protects the device from freezing.

Instead of a mechanical movement and a manual dial, digital pressure gauges use a strain gauge and a digital display. In addition, digital pressure gauges are usually equipped with an interface that enables remote data transmission. Digital pressure gauges therefore allow pressure monitoring without being directly on site. Another advantage is that the signal from the digital pressure measuring devices can be integrated into a control loop. If overpressure or underpressure is detected, the desired condition can be restored automatically by opening or closing a valve or pressure reducer. However, these high-tech pressure gauges are somewhat more complex and therefore more prone to faults. When mechanical and electrical components interact, there is generally a higher likelihood of failure.

In many cases, remote monitoring of internal pressures therefore uses a simple workaround: a manual pressure gauge is supplemented with a camera. This is sufficient for basic monitoring. However, the signal cannot be integrated into a control loop in this way and still requires manual monitoring.