compressor — air_leaks (flow-baseline)
Physics
Section titled “Physics”A compressed-air header’s total flow during a known no-production window (nights, weekends, scheduled breaks) should fall to a small, stable baseline that represents only normal system leakage and any always-on air-consuming equipment; if that off-shift flow rises above its learned baseline, the excess volumetric flow with no corresponding demand is, by elimination, leakage through a worn fitting, cracked hose, or failed solenoid somewhere on the header. An inline thermal mass or vortex flow meter on the main header continuously measures volumetric flow (SCFM); feeding that signal into an excess-over-learned-baseline detector during off-shift windows isolates the leak signature from production-driven flow swings. This recipe reuses the energy detector’s generic excess-over-baseline math on a flow signal instead of true kW: the detector’s power_signal/off_kw/min_excess_kw fields are historically named for electrical power, but the underlying sigma-multiplier-over-baseline logic is unit-agnostic, so here those fields carry SCFM values instead. The relevant dynamic is the slow drift of system-wide leak flow over minutes to hours, not any fast valve transient; sampling the flow meter at 1 Hz gives ample margin by Nyquist over that drift’s bandwidth while still resolving step changes when individual branch solenoids open/close during a no-demand window.
Sensor
Section titled “Sensor”- Spec: inline thermal mass or vortex compressed-air flow meter, 4-20 mA / Modbus output
- Signal: scalar (m3/min), range n/a
Example parts
Section titled “Example parts”- SMC PF3W740-N20-2 inline digital flow switch/meter (compressed air, 4-20 mA + Modbus output)
- Festo SFAB-600U-WQ6-2SA-M12 inline flow sensor (compressed air, analog + IO-Link output)
- ifm electronic SD6000 inline flow sensor (compressed air, analog + switching output)
Mounting
Section titled “Mounting”Install the flow meter inline on the compressor’s main header, downstream of the receiver tank and any dryer/filter train, at a straight-pipe run meeting the manufacturer’s minimum upstream/downstream diameter clearance (typically 10x pipe diameter upstream, 5x downstream) to avoid turbulence error. Orient per the manufacturer’s flow-direction arrow; depressurize and lock out the header section before cutting in the meter’s process connection.
Wiring
Section titled “Wiring”Meter’s 4-20 mA analog output or Modbus RTU/IO-Link output goes to an analog/serial input on the edge box; for a 4-20 mA loop, use a shielded twisted pair and ground the shield at the edge-box end only to avoid a ground loop with the compressor room’s electrical equipment.
Validation
Section titled “Validation”during a confirmed no-demand window, manually open a known branch isolation valve to simulate a leak of a known approximate flow (or use a calibrated orifice) and confirm the detector raises an excess-flow event; then close it and confirm the detector clears within close_after_clean samples
Expected: detector flags the simulated leak within open_after samples of the injected flow increase and clears within close_after_clean samples of its removal, with no false flags during the preceding baseline-learning window
Safety notes
Section titled “Safety notes”- a qualified/licensed electrician must verify and lock out (LOTO) any electrical supply to the flow meter’s transmitter electronics before wiring, using a CAT-rated meter appropriate to the transmitter’s supply voltage class
- depressurize and lock out the header section (bleed residual air pressure, verify zero pressure gauge reading) before cutting into the pipe to install the meter’s process connection; compressed air released suddenly from a cut line is a projectile and noise hazard
- wear eye and hearing protection when bleeding down or working near an active compressed-air header
300–1200 USD, difficulty 3/5, ~60 min install downtime.