For coarse granular materials such as sand, granulated sugar and alumina, that have poor air retention properties, the relationship will generally be similar to that of material type B. With these materials a minimum conveying air velocity of about 13–16 m/s is usually required to convey the material. These materials are not usually capable of being conveyed in any mode other than suspension flow with conventional pneumatic conveying systems. There is, therefore, little change in value of the minimum conveying air velocity that can be used to convey the material. Maximum values of solids loading ratio that can be achieved are generally quite low. A typical maximum value is about 15 but this can be as high as 30 if the pressure gradient is very high.