1) How does a combination gauge work?
A combination gauge contains two sensing elements inside one instrument:
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Pressure: a Bourdon tube flexes with pressure and turns the pressure pointer across a bar/psi scale.
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Temperature: either a bimetal coil (expands with heat) or a gas-actuated system (bulb, capillary, and pressure cell) moves the temperature pointer across a °C/°F scale.
Because the systems are independent, one reading can drift or fail without affecting the other—handy for fault finding.
When to choose which:
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Bimetal = rugged, fast, local mounting, typical for HVAC and water.
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Gas-actuated = better remote sensing and wide ranges, stable for high temps or where the dial must be away from heat.
2) Boiler and heating applications
Boilers, calorifiers, and closed hot-water loops rely on a combo gauge to confirm:
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Cold fill and hot operating pressure stay within design limits.
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Flow/return temperatures are on target for efficiency and safety.
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Trip and relief devices are set correctly by reading real system conditions.
Good practice: fit a siphon on steam lines, use SS316 wetted parts for treated water/chemicals, and mount the dial at eye level for daily checks.
3) Reading the dial (without the squint)
Dual scales can feel busy. Try this sequence:
- Locate colors: e.g., blue = pressure, red = temperature (your dial may differ).
- Check units: bar/psi and °C/°F—use the unit your procedure specifies.
- Read set pointer (if fitted): compare actual needle to the set/drag pointer for quick “in-band/out-of-band” checks.
- Scan the red zone: many gauges add a colored zone or mark for maximum safe pressure/temperature—stay below it.
Tip: choose larger dials (100–160 mm) for plantrooms; the extra diameter dramatically improves readability.
4) Troubleshooting common issues
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Fluttering or unstable pressure pointer
Likely pulsation from pumps or control valves. Fit a snubber/restrictor, use glycerine-filled cases, or move the take-off point. -
Temperature lags or seems low
Check for poor thermal contact. On steam/hot water, add a thermowell with heat transfer compound; verify the bulb is fully immersed (gas-actuated). -
Both readings drift over time
Vibration/over-range can deform the mechanism. Inspect mounting, add vibration isolation, and replace if accuracy is critical. -
Condensation in window
Choose liquid-filled or sealed IP-rated cases; relocate away from humidity swings. -
Inaccuracy after shutdowns
Re-zero if your model allows, otherwise bench-check against a reference and replace.
5) Replacing a combination gauge (bottom vs rear entry)
- Match the basics: dial size, range(s), accuracy, connection size (¼” or ½”), thread (BSP/NPT), and entry (bottom or back).
- Confirm materials: Brass/Bronze for clean water/air; SS316 for steam, chemicals, or corrosive media.
- Choose filling: dry for stable lines; glycerine-filled for vibration.
- Isolate and depressurize the line. For steam, allow to cool.
- Remove with two spanners (hold the process fitting to avoid twisting the line).
- Seal & install: apply suitable thread sealant, tighten to manufacturer torque, ensure the dial faces forward and is readable.
- Leak test and function check both pointers against known conditions.
Blanes can help
Share your medium, ranges, connection, mounting, and environment—we’ll size the correct replacement or upgrade and advise on snubbers, thermowells, or siphons for long service life.
Read more;
We also offer SANAS traceable calibrations complete with a certificate, valid for 1 year on our premises.
Blanes Pressure Solutions supplies a comprehensive range of pressure measurement instruments.
Blanes Pressure Solutions was founded in 2002 to take over the pressure business of Blanes Instruments CC, and can trace its pedigree back to 1893, when Robert Blane left Scotland to make his fortune on the Witwatersrand.
For more information on placing orders, after care and maintenance services you can contact our Sales Manager Ronel Olivier on ronel@pressuresolutions.co.za or 011 422 1749.
