| Decision | What to write on the enquiry | Why it matters |
|---|---|---|
| Range | 0-16 bar, 0-250 mbar, -1 to 24 bar | A gauge run near full scale fatigues fast; one run at 10% cannot be read accurately |
| Dial size | 63 / 100 / 150 mm | Reading distance and panel cut-out |
| Accuracy class | 1.0 / 0.5 / 0.25 as per EN 837 | Higher class costs more and needs recalibration more often |
| Connection | 1/2" NPT bottom, 1/4" BSP back | Bottom for pipe mounting, back for panel |
| Case and wetted material | SS304 case, SS316 wetted | Ambient corrosion vs process corrosion are separate questions |
| Filling | Dry / glycerine / silicone | Damping on vibration; silicone below -20 °C |
| Mounting | Direct, panel, surface, with bracket | Decides the connection position |
| Accessories | Siphon, snubber, isolation valve, over-range protector | Cheap parts that multiply gauge life |
Aim to have the normal reading between half and three quarters of full scale. A 0-100 bar gauge on a 6 bar line is unreadable; a 0-6 bar gauge on a 6 bar line will be at full deflection all day and the Bourdon tube will take a set within a year.
63 mm if the operator stands at the gauge. 100 mm for panel and skid work. 150 mm if it must be read from a walkway. Bigger dials also carry finer graduation, which is wasted if nobody can get close.
Class 1.0 covers almost all process duty. Class 0.5 and 0.25 belong on test benches and calibration rigs, and they need recalibration more often to stay worth the money.
The case fights the weather; the wetted parts fight the process. A coastal plant may need an SS316 case with ordinary SS316 wetted parts, and a chemical plant the reverse.
Glycerine filling damps pointer flutter from pumps and compressors and roughly doubles service life. Below about -20 °C ambient, glycerine thickens — use silicone. On oxygen service, use neither without checking compatibility.
A siphon on steam keeps the Bourdon tube out of live steam. A snubber on reciprocating service damps pulses. An isolation valve lets you replace the gauge without a shutdown. Together they cost less than one replacement gauge.
A gauge is normally good to about 200 °C at the connection. Above that you need a siphon, a cooling element or a remote seal — and if you do not say the temperature, we cannot warn you.
Gauges themselves are mechanical, but the accessories and any electrical contacts are not. If the point is in Zone 1 or Zone 2, say so with the gas group and temperature class.
Bourdon gauge with a siphon and an isolation valve. Never mount a gauge directly on a live steam line.
Glycerine filled gauge with a snubber. Pulsation is what kills gauges on this duty.
Diaphragm seal gauge with a flush diaphragm — a plain Bourdon tube will block.
Choose a full scale roughly 1.5 to 2 times your normal working pressure, so the pointer sits between half and three quarters of the dial in normal operation.
It is the accuracy class under EN 837 — the error stays within 1.0 per cent of full scale span. On a 0-16 bar gauge that is ±0.16 bar.
If the gauge is anywhere near a pump, compressor or vibrating skid, yes. The filling damps the pointer and roughly doubles the life. On still service it is unnecessary.
Yes. The siphon holds a plug of condensate so live steam never reaches the Bourdon tube. Without it the gauge will drift and eventually fail.
The case protects against the outside — rain, salt air, washdown. The wetted parts touch the process. They are chosen for different reasons and are often different materials.
Send the working and design pressure, the medium and the connection. We will size the range, pick the filling and list the accessories that matter.
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