What is a low differential pressure gauge?
A differential pressure gauge shows the difference between two pressures. Low-DP gauges are built for very small differences — often measured in millimetres or inches of water column or pascals — which ordinary bourdon-tube gauges cannot read accurately.
Common applications
- Filter monitoring: pressure drop across air filters, bag filters and cartridge filters rises as they load; the reading shows when to clean or replace.
- Cleanrooms and labs: room-to-room pressurisation keeps contamination out (or hazardous air in).
- HVAC ducts: static pressure and airflow balancing.
- Boiler and furnace draft: furnace and stack draft measurement.
Magnehelic, Photohelic or something else?
| Instrument | What it does | Choose it when |
|---|---|---|
| Magnehelic gauge | Dial gauge using a magnetic linkage — no fluid | You need a clear local reading of low DP |
| Photohelic switch/gauge | Gauge plus adjustable high and low set points | You need a reading and alarm/control contacts |
| Minihelic gauge | Compact low-DP dial gauge | Panel space is limited |
| Manometer | Liquid column or digital handheld | Reference checks, commissioning and troubleshooting |
| DP transmitter | Electronic 4–20 mA or digital signal | The value must go to a PLC, DCS or BMS |
How to select a gauge
- Range: choose a full scale so normal readings fall around the middle of the dial.
- Units: match the units your maintenance team uses (Pa, mm WC, in WC).
- Medium: standard low-DP gauges are for air and compatible gases; check the specification before using them with other media.
- Mounting: surface, flush or panel; some gauges must be zeroed in their mounting position.
Installation tips
Use the high-pressure port on the side with higher pressure, keep tubing short and free of kinks, and zero the gauge with both ports open to the same pressure before commissioning.
Frequently asked questions
Why does my filter gauge read zero?
Check that tubing is connected to the right ports, that it is not blocked or kinked, and that the gauge has been zeroed.
Can a Magnehelic gauge be used outdoors?
Use a weatherproof or protected variant, or install it in a suitable enclosure.
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