Pressure gauges – used to indicate the fluid pressure in a hydraulic system.

A hydraulic manometer is a central testing and measuring instrument that monitors and displays the system pressure in hydraulic systems. It is indispensable for operational safety, process optimization, and fault diagnosis in systems such as construction machinery, industrial plants, presses, and lifting equipment. It helps prevent over- or under-pressure and thus ensures the service life and efficiency of hydraulic components.

The most common type of hydraulic manometer, the Bourdon tube pressure gauge, works mechanically. Inside there is a curved tube spring that straightens under pressure. This movement is transmitted via a linkage mechanism to a pointer that displays the current pressure on a scale. There are also digital variants that use strain gauges and offer electronic displays as well as remote transmission options.

A hydraulic manometer typically consists of a case, a connection (usually with standard thread), a curved tube spring (Bourdon tube), a linkage mechanism, and a display with pointer and scale. For the inner tube/tube spring, brass is used as standard, with stainless steel or special materials such as PTFE for aggressive media. The case can be made of steel, stainless steel, brass, or plastic, while the display is protected by clear glass or a plastic window.

Many hydraulic manometers are filled with oil or glycerin. This filling fluid has two main functions: It dampens the display during vibrations, which improves readability and increases precision, and it protects the instrument from cold by stabilizing the internal components. This contributes to the longevity and reliability of the manometer, especially in demanding operating environments.

Hydraulic manometers are available in various case diameters, typically 40, 50, 63, 80, or 100 mm. The pressure ranges vary greatly depending on system requirements and commonly range from 0–250, 0–400, 0–600 up to 1000 bar or more. When selecting, it is important that the normal working pressure does not exceed more than 2/3 of the scale end value to ensure optimal service life and accuracy.

The correct selection of a hydraulic manometer is crucial for its performance and service life. Important criteria are:

• Pressure range: Slightly above the maximum operating pressure, working range max. 2/3 of the scale end value
• Materials: Bourdon tube (brass for standard, stainless steel for aggressive media) and case must be compatible with the medium and environment.
• Case filling: Glycerin/oil for vibrations, dry for quiet operation
• Display diameter: At least 63 mm for good readability
• Connection: Correct size and position (e.g., 1/4" bottom or rear)
• Accuracy class: 1.6 or better for critical applications

Manometers are screwed into measurement connections or test line T-pieces and can be replaced if necessary. For long service life, regular maintenance measures are important: checking calibration, inspecting for damage, replacement in case of leaks, and occasional visual inspection of pointer deflection. Tightness and media compatibility must also be checked. Good hydraulic oil quality and effective filtration also contribute to longevity.

Various hydraulic manometers are available commercially that differ in pressure range, connection, and other specifications. For example, there are manometers with a pressure range of 0–250 bar or 0–400 bar. Common connections are 1/4 inch, often with connection positions at the bottom or rear. A diameter of 63 mm and an accuracy class of 1.6 are standard. Some models are already filled with glycerin, which increases shock and vibration resistance. When purchasing, care should be taken that the specific requirements of the hydraulic system (pressure, environment, compatibility) match the characteristics of the manometer.