For shipping container projects that require a pressure-relief valve that meets SAE AS27166 (formerly MIL-DTL-27166), use this calculator to determine the minimum flow rate requirement. This calculator can be used as a rule-of-thumb for other containers (as long as ambient pressure change rates are lower than that of a military cargo plane):
The minimum flow rate to protect the container is 12% of the container internal volume of the container, per minute.
Per the standard, the minimum flow rate shall be determined at a differential pressure of 1.5 psi greater than the specified reseal pressure. However, the standard was written with the assumption that the flow rate of the valve is minimal below this pressure. Stratotech valves are designed to provide a higher flow rate at lower pressures. If this standard does not apply, use the following procedure:
- Determine the maximum pressure the container or enclosure can withstand for an extended period.
- Cross-reference the required flow rate calculated here with the differential pressure of a particular valve at that flow rate. More than one valve may be required.
- For example, the BV2000-05-05 has a flow rate of 30 cfm at 0.75 psi. If a flow rate of 30 cfm is required based on your container volume, you can expect to see 0.75 psi differential pressure and vacuum.
The displaced volume of the material in the container may be subtracted from the container volume. Do not subtract the volume of material that may be removed during shipping.