Dimensioning of a silo often starts – if not limited by available space – with a certain capacity requirement. We hear you think: “That’s easy!”. Length multiplied by width and height gives you the capacity in m3. Times the specific gravity gives you the tons. True and indeed easy.

As often practice is much more nuanced. The above theory is just a quick method resulting in the gross capacity. But in practice you are interested in the net capacity of the silo.
So what actually determines the net capacity?

1. Wall type: a profiled wall silo gives you more net capacity than a smooth wall silo.
2. Hopper shape: the bigger the hopper outlet and the steeper the angle, the more net capacity.
3. Product angle of repose: the steeper the angle of repose, the less net capacity.
4. Inlet position: the further the product inlet is removed from the center, the less net capacity.

The relative influence of point 2-4 grows when the silo height decreases. Percentagewise, capacity might reduce drastically from gross to net in case of silos with a limited height.

Please have a look at the sketch below which visualizes this subject.