PRESSURE MEASUREMENT TECHNOLOGIES
Pressure gauges: a local reading with no power and no wiring
A pressure gauge shows the pressure on the spot, on a dial, with no power, no wiring and no configuration — the simplest pressure instrument and still the most common one in any plant. A good gauge is chosen for the medium, the range, the accuracy class and the safety it offers when something goes wrong. Our catalogue includes the Delta Mobrey GS safety-pattern gauges and the CP stainless steel gauges for low pressures.
How a pressure gauge works
Most gauges use a Bourdon tube: a curved tube of oval cross-section, closed at its tip. When pressure enters it, the tube tries to straighten and its tip moves a little. A link transmits that motion to the movement — a toothed segment and a pinion — which turns the pointer over the dial, in proportion to the pressure.
For low pressures a Bourdon tube is not sensitive enough; under EN 837-1 its ranges start at 0.6 bar. Low pressures use a diaphragm or a capsule, covered by EN 837-3, which give a larger movement for a small pressure. The Delta Mobrey CP is a stainless steel gauge for low pressures on dry gases, air and exhaust streams.
Accuracy is stated as a class under EN 837: classes 0.6, 1.0, 1.6 and 2.5 allow an error of that percentage of the full scale. A class 1.6 gauge with a 0–10 bar scale, for example, is within ±0.16 bar across the scale.
Safety matters when a gauge fails under pressure. The GS is a solid-front safety-pattern gauge: a baffle wall separates the pressure element from the dial, and a blowout device in the backplate vents the pressure backwards, away from the person reading it. The CP also has blowout protection. Both are stainless steel; the GS has ranges up to 4,000 bar and an ATEX option.
- The pressure, entering the Bourdon tube through the connection stem
- The movement, which turns the motion of the tube tip into the rotation of the pointer
- The angle of the pointer rises in a straight line with the pressure
Where a pressure gauge fits — and where it does not
A strong choice for
- Local indication on pumps, compressors, filters and vessels, for the operator walking past
- Utility lines: compressed air, steam, water and gases
- A check next to a transmitter, to confirm the reading on the spot
- Points with no power or wiring, or where electronics are not wanted
- Very high pressures: the GS has ranges up to 4,000 bar
- Corrosive atmospheres: stainless steel cases such as the CP in AISI 316
Think twice when
- You need the reading in the control room, recorded or with alarms: a gauge sends no signal — use a transmitter
- The pressure is only a few millibar: a Bourdon tube is not sensitive enough — that needs a diaphragm or capsule gauge
- The pressure pulsates or the pipe vibrates, and the gauge has no snubber or damping: the pointer shakes and the movement wears
- The medium is viscous, crystallising or full of solids, and would block the gauge without a diaphragm seal
How it compares with the other technologies
- Pressure transmitters25 mbar…2000 bar
- Differential pressure transmitters10 mbar…70 bar *
- Pressure switches10 mbar…400 bar
- Pressure gauges (the technology of this article)10 mbar…4000 bar
Typical ranges, not a model commitment, on a logarithmic scale. For differential pressure transmitters (*), the range is that of the difference; the static pressure of the line can be much higher. We confirm the figures of each instrument for your application.
Installing a pressure gauge
Mount the gauge where it can be read easily, with a valve between gauge and process, so that it can be changed without stopping the line. A dial size of 100 mm or more is easier to read from a distance; the GS comes in 100, 125 and 150 mm, the CP in 100 and 150 mm.
Then:
- Choose the range so that the normal pressure sits in the middle third of the scale.
- Where the pressure pulsates, fit a snubber; where the pipe vibrates, ask for a damped gauge.
- Leave free space behind a safety-pattern gauge, so that the blowout back can open.
- For an alarm at a limit, a single or double electrical contact can be added to the gauge.
Pressure gauges by industry
Pressure gauges in our catalogue
The pressure gauges in our catalogue, each with its own page and technical data.
Pressure gauges: frequently asked questions
Ask about a pressure gauge
Tell us the medium, the pressure range, the dial size, the accuracy class, the process connection and the mounting — and our engineers will suggest the right gauge, with price and delivery time.