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This International Standard specifies a method of measuring unit pressure loss in one-dimensional air flow through bulk grain, permitting calculation of the total pressure loss of a ventilation unit. This is equal to the sum of the pressure losses

• in the ventilation system (ducts, etc.);
• in the grain (which is the subject of this International Standard);
• due to the passage of the air from the duct into the grain.

The pressure losses in the ventilation system and those due to the passage of the air from the duct into the grain can be considered as negligible in relation to the pressure losses in the grain if the air flow velocity does not exceed the following limits:

• 8 m/s to 10 m/s in the main duct;
• 4 m/s to 5 m/s in the secondary duct;
• 0,25 m/s when entering the grain.

If, for economic reasons, air velocities are higher than those indicated above (up to 30 m/s in the main duct), then, following pertinent literature, the pressure loss caused by the air distributing and discharging system has to be calculated.