Subscribe to our monthly newsletter.

Share this item

1. Make sure that you know the full range of conditions of the material to be stored. Secure an officially verified, ’fully representative’, sample and check that it is of consistent supply, from a homogeneous stock and stable in time and under the relevant operating conditions, - or know the reason why. Check what will be ‘worst’ condition.

2. Measure wall friction every time with options of the wall contact material. There is no ubiquitous ’Low Friction’ material, it depends upon both the product and the contact surface. Also, wall slip depends almost entirely on wall friction. It is easier to promote flow than generate wall slip if the slope of the hopper wall is inadequately steep. Getting the wall angle right is a most important design feature.

3. Establish, and allow for, any extended periods of storage. Not just in normal use, but for reasons of production campaigns, holidays, breakdowns, or irregular stoppages.

4. Check whether the ambient conditions alter according to production conditions, weather, season or events such as site wash-downs. Is there local vibration?

5. In the first instance, distinctly separate issues of Reliable Flow from Mass Flow of the whole hopper contents. Although a Mass Flow design helps material to flow through smaller outlets than a Non-Mass Flow pattern, it does not necessarily have to apply to the total contents. The choice for selecting total Mass Flow depends on how the product is affected by indefinitely extended storage or a need to counter segregation. An ’Expanded Flow’ construction bestows the flow benefit of Mass Flow on the hopper outlet region. See Ajax notes on advantages and drawbacks of mass flow.

6. Ensure by design and fabrication that there are no surface impediments to smooth surface slip. Weld spatter or weld runs across the contact wall surface, offset flange joints, protruding gaskets, recessed ports and projecting intrusion near the outlet are highly effective at opposing the slip of material on wall surfaces.

7. Allow a flanged joint well clear of the outlet and a little spare headroom, so that access is available or a new outlet can be retrofitted in the event of flow difficulties.

8. Consider fitting a valve of a larger size than the final outlet, and converge below. Materials will flow through a smaller opening than that required to initiate flow, particularly if hopper contents time consolidates.

9. Be aware that circular bins ’ring’ like a bell when vibrated. They have inactive nodes at 45° to the initiating point. If fitting two vibrators, install them at 45° horizontal spacing, as near as practical to the outlet and activate them alternately only when flow is required and not occurring. Do not be bashful about considering flow assisting devices.

10. A vital region for flow is the outlet zone. ‘V’-shaped hoppers are twice as effective for outlet size than cones, need lower wall angles and increase capacity. Good reasons for fitting a feeder.

For reliable flow when the final outlet size is limited use a planar transformation, preferably with * ’Sigma Two’ relief. If you have to bang the hopper, it is not properly designed. Fix it before it gets worse, as it will. (see Ajax technical articles for explanation of Sigma Two relief, and use of inserts to improve flow).