Sand testing · permeability

Permeability meter calibration

Permeability is an air-flow measurement, so calibrating the meter means proving it against a known, traceable flow - the laminar-flow nozzle.

By Versatile · equipment manufacturer & calibration provider · updated 2026-07-15

What permeability measures

The permeability number expresses how readily air passes through the rammed sand specimen - a direct predictor of whether mould gases escape or turn into blows and pinholes. Iron foundries typically hold a permeability number around 100-200. The meter times a fixed air volume through the standard AFS specimen (or reads flow at a set pressure), so everything depends on the meter measuring flow and pressure correctly.

The nozzle calibration method

A permeability meter is calibrated against traceable laminar-flow (orifice) nozzles of known characteristic - commonly a 4 mm and an 8 mm nozzle that stand in for a low and a high permeability. Each nozzle has its own calibration certificate traceable to national standards (NIST or equivalent).

Fit the nozzle in place of a specimen and run the meter as if measuring sand.
Compare the meter's permeability reading against the nozzle's certified value at the working pressure.
Repeat for each nozzle (low and high), record error, adjust if the design allows, and re-check.
Verify the manometer / pressure reading, since permeability is derived from pressure and flow together.
Issue a certificate citing each nozzle's certificate number and traceability.

The nozzles are the reference - their certificates are your traceability. Keep them in date; an expired nozzle certificate invalidates the calibration that relied on it.

The monthly primary check

Between full calibrations, a good practice is a monthly primary check: run the traceable 4 mm and 8 mm nozzles and confirm the meter still reads within tolerance. It takes minutes, catches drift and leaks early, and gives an auditor a continuous record of control rather than one annual data point.

Interval

Full calibration is commonly annual for a production meter, supported by the monthly nozzle check. Set and justify the interval from usage - see intervals & IATF 16949.

Leaks and other errors

Air-path leaks - the classic fault; they read as falsely low permeability. Check the specimen seal, gaskets and tubing.
Blocked or dirty orifice in the meter or nozzle.
Manometer error - wrong pressure quietly biases every reading.
Wrong or worn specimen tube - changes the flow area, exactly as it does for strength.

Frequently asked questions

How is a foundry permeability meter calibrated?

By running traceable laminar-flow (orifice) nozzles - commonly a 4 mm and an 8 mm - in place of a sand specimen and comparing the meter reading against each nozzle’s certified value at the working pressure, while also verifying the manometer/pressure reading. The nozzle certificates provide traceability to national standards.

What is a good permeability number for green sand?

Iron foundries typically target a permeability number of roughly 100-200, but the right value depends on the casting, metal and moulding method.

Why does my permeability read low?

The most common cause is a leak in the air path - a poor specimen seal, a bad gasket or cracked tubing - which lets air bypass the sand and reads as low permeability. A blocked orifice or a manometer error can also bias the reading.

Calibrate with the people who build the equipment

Versatile manufactures foundry sand testing and metallurgical instruments and calibrates them with traceable certificates - the original-equipment-manufacturer route recognised under IATF 16949 cl. 7.1.5.3.2.

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