Over a distance of 500 m the pressure gradient is too low to convey the type A material in dense phase. The maximum value of solids loading ratio is less than seven and so the conveying limit now relates to a minimum conveying velocity of about 11 m/s. That for the type B material is still 15 m/s and so the two sets of conveying characteristics occupy a similar space. The significance of this is that there will have to be a significant increase in air flow rate to convey the type A material, but not for the type B material.