In brief
A pressure gauge is an instrument that displays the pressure of gases or liquids, in industry usually as a mechanical local dial instrument.
Contents
What is Pressure gauge?
Pressure gauges display the pressure directly at the measuring point, for example on pumps, compressors, hydraulic power units, compressed air service units or vessels. The most widespread type is the Bourdon tube pressure gauge to EN 837-1: a curved Bourdon tube straightens under pressure, and a movement transmits this motion to the dial. Diaphragm and capsule pressure gauges are suitable for low pressures and for aggressive or viscous media. They need no auxiliary power and therefore remain readable even during a power failure.
Key parameters are nominal size (case diameter), scale range, accuracy class, process connection with thread and position (bottom or back mount), materials of the measuring system and case, and any liquid filling, which damps pointer oscillation caused by pulsation and vibration. For special cases there are diaphragm seals, contact pressure gauges with a switching function and differential pressure gauges. Diaphragm seals separate the instrument from the medium by means of a diaphragm, for example with hot, crystallising or hygienically sensitive substances. The accuracy class states the permissible deviation as a percentage of the full-scale value.
Pressure gauges fail due to overload, pressure surges, vibration, corrosion or blocked connections. A sticking pointer, or one that does not return to zero, is a clear signal for replacement. Pressure gauges at important measuring points are regularly compared with a reference instrument.
In practice: maintenance and procurement
For a replacement, the nominal size, scale range, unit, accuracy class, connection thread and position, materials and, where applicable, filling are needed. Choose the scale range so that the operating pressure lies as far as possible in the middle third of the scale; this protects the measuring system.
Synonyms and abbreviations: manometer · Bourdon tube pressure gauge · pressure indicator · dial pressure gauge
Frequently asked questions
What is the difference between a pressure gauge and a pressure sensor?
A pressure gauge displays the pressure locally, usually mechanically and without auxiliary power. A pressure sensor converts the pressure into an electrical signal that is transmitted to a controller and evaluated there. Both are often combined at the same measuring point: the gauge for visual checks, the sensor for control and alarms.
What is the glycerine filling in a pressure gauge for?
The liquid filling, often glycerine or silicone oil, damps pointer oscillation caused by pulsating pressure and vibration, for example on pumps or compressors. This makes the value easier to read and protects the movement. For certain media, such as oxygen, special fillings or unfilled instruments are mandatory.
What information is needed to order a pressure gauge?
Needed are nominal size, scale range and unit, accuracy class, connection thread, connection position bottom or back, material of case and measuring system, medium, and whether a filling or a contact is required. If the old instrument is still legible, the dial contains most of this information.