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Obtaining Reliable Flow From Existing Hoppers: Strategy for Selecting the Solution

Dr MSA Bradley
The Wolfson Centre for Bulk Solids Handling Technology University of Greenwich, London SE18 6PF


It is common to have to deal with existing hoppers and silos which do not discharge reliably. The engineer faced with such a problem needs some sort of understanding of how to select the most appropriate of the many possible solutions available. The choice depends upon consideration of:-

The many types of mechanical extractors, vibrating flow aids, pneumatic devices and other options each have a place, but the selection of the wrong approach can lead to disappointment or even a worsening of the problem. However, even given the choice of the appropriate device, the way in which it is applied can make the difference between success and failure.

This paper seeks to give a general understanding of the principle of employing aids to flow, and develop some guidance to the engineer as to how to approach the problem, choose the solution most likely to be successful, and apply it in the best way.


1.1 Core flow discharge and hopper obstructions

There are basically two possible flow patterns in hoppers, i.e. core flow and mass flow, as depicted below. Although mass flow has some useful advantages, the vast majority of vessels discharge in core flow. This is because achieving mass flow requires some very careful design, usually following flow testing of the product being stored; in practice this is not often done, consequently the “default” pattern of core flow is instead arrived at. The specific advantages of mass flow will be explored later in this paper.

Fig. 1a Mass flow
Material all in motion, sliding on the cone of the vessel and coming out in order of input

Fig. 1b Core flow
Material sloughs off the top surface down an angle of repose and flows down through a central flow channel

1.2 Ensuring reliable core flow

Failures to discharge from core flow hoppers can occur as a result of two different types of blockage, the stable arch or the rat-hole as shown below.

Fig. 2a Stable arch

Fig. 2b Stable rat-hole

These are both stable structures in which the strength of the bulk solid is higher than the stresses in the structure (from its self-weight), meaning that the structure will not collapse under its own weight. The stresses in the structures increase as the size of the structures (arch or rat-hole) increase; the size of the structure is dictated by the outlet size of the vessel, hence it follows that if the outlet size of the vessel is continually increased, there will eventually arise a situation where the stresses in the structure overcome the strength of the material and the structure collapses, allowing flow to occur.

Any given commodity has a certain strength characteristic, which effectively gives it a maximum dimension across which it can arch, and a maximum size of rat-hole which it can support. These dimensions depend to a degree on the size of the bin and hence the pressure applied to the material at the bottom to compact it, and also on the maximum time in residence between complete emptyings-out of the bin (this “time consolidation” effect can also strengthen the material).

The important point to understand from the above is this: For a given commodity in a given vessel, there is a certain maximum arching dimension and a certain maximum rat-hole dimension which the commodity can support. As it happens, the maximum rat-hole dimension is usually much larger than the maximum arching dimension. If the outlet of the vessel is below the arching dimension of the material, an arch will result when material is withdrawn; if the outlet of the vessel is above the arching dimension, but below the rat-hole dimension then a stable rat-hole will form once the material in the centre of the bulk has flowed out (unless the bin operates in mass flow in which case a rat-hole cannot form).

Thus, for a core flow bin to discharge successfully by gravity, without flow aids, the outlet size would need to be above the maximum stable rat-hole dimension of the commodity being stored. In bins where there is not a problem with flow, this is the case. However where there is a flow problem, clearly it is not.

One option is to enlarge the outlet dimension above the maximum stable rat-hole dimension. If this is too big to connect directly to the equipment under the vessel, then a mechanical feeder of some kind is needed to take the commodity from this large hopper outlet and feed it into the smaller equipment underneath. This approach, whilst workable, is not always possible or desirable, especially as the stable rat-hole dimension of the commodity can often be several feet with cohesive materials.

1.3 Successful application of flow aids

objective of a flow aid is effectively to turn the lower section of the hopper into a feeder, by artificially encouraging flow of the contents where such flow would not occur under gravity alone. An effective flow aid must therefore encourage flow down to the mouth of the hopper, and all the way up to a diameter above the stable rat-hole dimension of the commodity.

One point to note is that if the commodity has a high tendency to “time consolidate” (i.e. gain strength with time) then the maximum stable rat-hole diameter will be very large, sometimes even as large as the vessel containing it. This is a particular problem with a core flow hopper, since with this flow pattern, the material around the hip will remain static all the time until the hopper is actually emptied right out. In such a case, for a flow aid to be successful, it has to activate the entire height of the converging section. However, for materials with such a high tendency to time consolidate, it is probably more economic in the long term to change to a mass flow hopper for reasons which will become apparent later.

Fig. 3 Application of flow aids to a core flow hopper for successful discharge

The many different types of flow aid work in different ways to achieve the same objective. Their ranges of applicability, and particular points to be watched when using them, will be explored below. Of course, the critical rat-hole dimension of the material in the hopper is often not known (although it can be determined by flow property measurement) but a general understanding of the above principle is necessary to ensure the successful use of discharge aids.

1.4 Available options

Briefly, the most commonly employed aids to improved flow are:-

These will be taken in turn and their applicability examined.


Vibration is probably the most commonly-applied aid to discharge. It works extremely well to control the flow of free-flowing materials; ironically, discharge aids are rarely needed for such materials! However, they can be used for quite a wide variety of commodities provided the commodities are not either:-

2.1 External vibrators

Vibrators bolted to the outside of a vessel vibrate the wall, thereby reducing the friction between hopper and contents and (to a small degree) reducing the strength of the bulk. The reduced wall friction undermines any arch and puts an inwards pressure on any rat-hole, helping to collapse it.

To be effective, external vibrators must be applied in the right place, that is to vibrate the hopper wall in the region between the outlet and the critical rat-hole diameter, as shown in fig. 3 above. This presents something of a problem, since the area around the mouth of the hopper is its strongest part; frequently, it is bolted to a rotary valve or other heavy piece of equipment. Consequently, getting the vibration to transmit into this part of the structure is not easy. Nevertheless it is important that the vibration is carried as far down the wall towards the outlet as possible, as this is the most critical area for flow (being the smallest). If vibrators are fitted too high up, then flow will be encouraged high up which will simply serve to apply pressure to the material lower down near the outlet of the hopper and consolidate it, making it harder to discharge.

In general, it is best to start with vibrators low down on the hopper since the vibration will transmit upwards into the more flexible part of the structure, more readily than downwards.

Such external vibrators are usually installed as a first retro-fit option to a troublesome hopper; they are quite cheap, readily available and easy to install. Positioning has been mentioned; sizing is rather more hit-and-miss but suppliers can advise. Experience has shown that they are effective at overcoming slight flow problems (where discharge is mostly adequate but stops now and again and can be restarted with a bit of hammering). It can deal with more regular problems as long as the material is not highly cohesive. Often they do not need continuous running; just a fifteen-second period when flow is first initiated, or perhaps the same every minute during discharge. It is always better to start with too little vibration and increase it if necessary, to avoid the danger of compacting the material especially if the flow rate is limited under the hopper by a rotary valve or feeder.

Vibrators must always be sequenced so that they only come on when the material is being taken away from the hopper outlet; applying vibration to any material when it is confined will simply consolidate it.

Given the cheapness and ease of installation, the application of external vibrators is always worth a try unless the material is known to be highly cohesive or elastic or the discharge problem is extremely severe.

2.2 Internal vibrators

Where more severe flow problems occur it is better to install a well-designed internal vibrating flow aid. The most common include:-

2.2.1 Vibrating cones

In one realisation of these devices, the internal cone contains an air-driven vibrator and mounts inside the existing hopper cone on flexible mounts; examples include the well known “Soliflo” or “Matcon” devices. In other versions (e.g. the “bin activator”) the cone is mounted rigidly inside a conical or dish-shaped replacement hopper bottom, itself mounted on flexible mounts and driven by external vibrator motors. The first type can sometimes be retrofitted to an existing bin, whereas the second type requires the bottom of the hopper to be removed. Either can be designed in to new installation quite effectively.

In either case, the internal cone vibrates much more effectively than a hopper wall with a bolt- on vibrator. This promotes flow of the material right across the hopper from wall to wall, adjacent to the cone, by allowing flow down the surface of the cone and making it impossible for the material to arch between the hopper wall and the moving cone. Provided the diameter of the vibrating cone is nearly as large as the rat-holing dimension of the material, this will promote flow very well.

Vibration is applied continuously or intermittently all the time discharge is required, and when vibration is turned off the material arches between the static cone and the adjacent hopper wall. Again, vibration must not be applied unless the material can discharge freely beneath the cone.

These devices have been used very extensively for a wide range of materials, and found to be successful provided the material is not either highly cohesive or highly elastic, as described above. Sizing of such a device presents a challenge, as selecting too small a unit (below the stable rat-hole dimension of the bulk solid) will result in poor performance. Many suppliers of these units will size the unit in relation to the diameter of the hopper, which is not strictly correct as an approach but usually meets with success for the simple reason that their recommendations often result in the specification of quite large devices; not uncommonly two or three metres across, which is above the maximum stable rat-hole diameter of many bulk solids.

In general, the best advice with these devices is to accept the supplier’s advice if they can show they have used one of the proposed size (or smaller) with the same bulk solid in the past, but be sure that the bulk solid is truly the same. If this cannot be shown, then it is better not to purchase the device until the supplier has proved its effectiveness with a sample of the bulk solid in a test set-up.

Again it is extremely important to ensure that the vibrator control is sequenced so that it cannot be run unless material is being taken away from the space underneath the device.

2.2.2 Internal screens

Some devices are available which consist of screens of perforated plate or similar, mounted parallel to the hopper cone surface on flexible mounts, and driven by an externally mounted vibrator. An example is the Mucon “Promo-Flow”.

Experience with these devices is much less widespread, however they have been shown to be effectiveness with some materials. If contemplating the use of such a device then a trial with the bulk solid to be handled is an absolute necessity.

2.2.3 Outlet-plane grid devices

There are on the market several devices which are effectively square screens or grids of a “louvre” pattern which fit horizontally across the outlet of a hopper, and vibrate to encourage the bulk solid to flow through the grid into a short vibrating chute beneath (examples are the “Hogan bin discharger” and the “Siletta discharge aid”). These work in effectively a similar way to the internal cone devices, promoting flow across their entire upper surface. Similarly to conical devices, to be effective such a device must be above the maximum rat-hole dimension of the bulk solid. Retrofits involve cutting the bottom off the existing hopper. Again a trial is recommended to ensure success with the particular bulk solid to be handled by such a device.


These are probably the second most common flow aid device. In general, aeration is most effective for finer materials, say under 20 to 40 microns median particle size. However, the presence of larger particles in a commodity which consists principally of fines will not compromise the effectiveness of aeration.

Aeration works in three ways:

3.1 Low level aeration

The “vacuum-breaking” effect is beneficial in almost any situation where a fine powder is being discharged. Even when a mechanical extractor or a mass flow hopper with a large outlet is used, the introduction of a very small amount of air (say a quarter to a third of the volume flow rate of bulk solid) will help keep the flow consistent in rate and density. This should be introduced at a level perhaps a quarter of the way up the cone. However, this approach will not promote flow where the hopper outlet is less than the maximum stable rat-hole diameter of the bulk solid, so is hardly really a flow aid in the terms of this paper.

3.2 Aeration as an active flow aid

A higher level of aeration applied at the proper location (between the outlet of the hopper and the rat-hole dimension of the bulk solid) can be used to actively promote flow. With bulk solids which fluidise well (low cohesiveness, hard particles and not too fine a particle size, such as fly ash or cement) the exact means of air injection is less critical than the choice of location; even installations as crude as holes drilled in the wall of the vessel, covered with a disc of filter fabric and with compressed air applied, can be very effective as the air will tend to distribute itself through the bulk solid. Such a crude installation is a cheap emergency retrofit on an existing vessel, whereas in new or properly redesigned installations a more sophisticated approach (as will be described below) is preferable.

With more cohesive materials such as flour, the air tends to make cracks in the material and blow through these without helping promote flow, and such a crude approach does not work. In such cases, aeration pads of sintered metal or plastic, or (better still) flexible fabric are needed to ensure proper distribution of the air. For best effectiveness, these pads need to be mounted all the way down to the outlet of the hopper, and as far up as is required to prevent rat-hole formation. Often, four lines of aeration mounted at 90 degrees to one another in plan view are found to be most effective. On larger installations (perhaps more than a couple of metres across) it is preferable to “zone” the air flow with a timer and solenoid valves to ensure that all pads receive a fair share of the air flow in turn irrespective of how much material is above them and hence the local resistance to air flow.

With the sort of approach described and bulk solids with good fluidisation properties, it is possible to design very large vessels with almost flat cones (fifteen degrees to the horizontal, or less) making very good use of space. However, such installations need very careful design by experts, and are not really in the realm of “flow aids”.

3.3 Very fine materials

For very fine materials such as titanium dioxide or similar, aeration cannot easily get in between the particles so the “reduced wall friction” effect is most effective, normally by lining the entire hopper cone with large segmented aeration pads. These aeration pads are best made from a good quality needlefelt fabric (as used for airslides) supported by perforated plate; sintered plastic or metal, or porous ceramics, have been used sometimes but tend to blind with the fine particles whereas fabric flexes and releases the particles. This approach is effective, but expensive not only in terms of equipment but also air consumption and maintenance. It can be retrofitted, at a cost. For new installations, the use of gravity-discharge mass flow hoppers is a more cost-effective solution.

3.4 Air blasters/air cannon

These devices are the exception to the general rule that aeration devices only work well with fine powders, since they are often used for coarser materials such as damp minerals. Firing an air cannon releases a small explosion locally to its injector point, dislodging bridged material. They have been used successfully to help move regular bridges of material from specific locations where flow is not reliable. General consensus suggests that they are best applied in situations where a hopper suffers only from local bridging, e.g. near an outlet. They are only really applicable to fairly large vessels where the energy released during firing can dissipate harmlessly, as if confined this energy can cause structural damage to the vessel itself. They can cause compaction of the bulk solid if applied incorrectly especially with fine powders; however their application is not well understood even amongst vendors of these units

3.5 General comments on aeration devices

For any aeration system, quality of air is of paramount importance. Water in the air, high moisture content which will be taken up by the bulk solid (or for that matter excessively dry air which will dry out the bulk solid) will cause caking of the bulk solid and make the problem worse. Maintenance of water traps etc. is thus critical.

One drawback of using aeration as an active flow promotion device is that it will tend to expand the bulk solid to a low and somewhat variable density, and can lead to variations in discharge rate. Where the absolute value of discharge rate is not terribly important this is not likely to be a problem, but in instances where careful rate control is required, such as when interfacing to a metering feeder, this will cause difficulties in obtaining proper control. (This comment does not apply to the use of aeration at a low level for “vacuum-breaking” as first described, which will help keep the bulk solid to a more consistent density.)

A final point to bear in mind is that aeration (with the exception of blasters) is likely to fail completely when applied to wet, very sticky or coarse materials. In fact it can even make flow problems worse by encouraging drying-out or segregation of such materials.


All the many types of mechanical dischargers have the same objective; to provide a physical gathering and pushing of bulk solid from across a large inlet dimension above, into a small outlet dimension beneath. This promotes flow very well across the inlet area of the device, and provided that the inlet is larger than the maximum rat-hole dimension of the bulk solid, reliable flow is assured.

With mechanical devices, large inlet dimensions can be achieved quite easily, albeit at a cost, so that even very cohesive bulk solids can be handled. In fact it is not uncommon to make the mechanical extractor the full diameter of the vessel so that no convergence is needed on the walls, and such an approach has the added benefit of giving effectively a mass flow discharge pattern in the vessel, thus promoting first-in-first-out storage, and eliminating long-term resident material which can go hard. This is practically a foolproof approach, as the bulk solid cannot hang up anywhere and will always discharge provided the extractor has the power to dig it out. It should be said that this extreme approach is not always required, and some systems work with mechanical extractors of more modest dimensions interfaced to core flow hoppers.

In either event, the point is that these devices can deal with highly cohesive materials which could not be moved by vibration, aeration or other less costly means. In general, they should only be considered where the flowability of the bulk solid is so poor as to make other options (including design for mass flow gravity discharge) impossible or uneconomic.

4.1 Sweep augers

These work by continuously undermining the inventory in the vessel ahead of the screw, and can cope with most bulk solids including damp materials unless they are either so sticky as to clog the screw flighting, containing long fibres which can wrap themselves around the screw, or lumpy and abrasive which would cause high wear.

They are subject to high forces so are strongly constructed with high-torque drives, hence are very expensive. One of the bigge*st potential problems with such devices is that they produce a rotating stress-field within the silo above, which can very easily destroy the silo unless it has been specially strengthened to an appropriate degree. This makes them almost impossible to retrofit. Screw breakages occasionally are a possibility especially if the screw hits some highly caked material, so it is worthwhile considering the pattern which allow for replacement of the screw without emptying the silo first, in a large installation.

A variation on the sweep augur which can be retrofitted to an existing vessel is the “circular bin discharger”, with an arch-breaker arm inside the cone of the silo driven from a universal joint at the outlet. The length of the arm is almost equal to the slope length of the hopper cone, and rotates slowly, being free to move and undermine the bulk solid. These devices are still expensive, but sometimes can be applied to an existing silo without the need to cut the whole bottom off the vessel. Again they can discharge materials for which gravity-discharge hoppers would be impossible. If intending to use such a device, a trial is essential.

4.2 Ploughs

Plough dischargers are not commonly used in the UK; although they offer useful advantages, their relatively poor availability has limited the experience available. Recently the Portasilo “Rotoflow” device has been introduced to fill this gap but it will be some time before wide experience of application is available.

4.3 Walking floor and sliding frame dischargers

The “walking floor” discharger consists of a flat silo floor divided into several strips, which oscillate alternately to and fro alongside each other. At one end of the assembly there is a gap down which the bulk solid falls when the moving strip retracts, from which it is fed by a screw. The “sliding frame” device again consists of a flat floor, but this time static with a frame sliding backwards and forwards on top of it and encouraging the bulk solid to fall into a slot across the middle of the floor, where again it is taken away by a screw. In each case the discharger mechanism is invariably the full size of the silo plan so there is no converging section.

This type of discharger was mainly developed to deal with bulk solids of the most severe flow characteristics, such as high water content, compressible, highly cohesive materials (e.g. partially dewatered sewage sludge, paper pulp waste etc.) which cannot be handled by any other means. As such they are capable of dealing effectively with these materials, but the equipment cost is very high. These should be considered only when dealing with the most extreme cases of poor flowability.


Gravity is very reliable in itself - it never breaks down or needs maintenance. However, the amount of work available from gravity is strictly limited according to the height available. That means that for bulk solids which are cohesive, and which hence require a significant work input to deform them in flowing down a hopper cone, some care is needed to ensure that gravity alone can overcome the strength of the material.

With relatively free flowing materials, the short height of a cone on a core flow hopper yields enough work to make the material flow reliably. However for materials which have significant internal strength, the outlet size needed for reliable gravity core flow usually becomes unacceptably large (usually half a metre or more, often over a metre). In addition, the last material to be discharged in core flow will have been in static residence since the hopper was first filled (first-in-last-out), so if the material has any tendency to gain strength with time, this last material out will have become very strong in the intervening period and thus very hard to discharge.

5.1 Mass flow

It is in these two respects that mass flow comes into its own:-

Mass flow requires steeper and/or smoother walls in the cone of the hopper than does core flow. Just how steep, and what internal surface is best for the cone, depends on the frictional characteristic between bulk solid and hopper wall, so it is imperative to have flow tests undertaken with the bulk solid to determine the hopper geometry needed. In the absence of such flow tests, it is impossible to embark on the design of a suitable hopper, however once the flow characteristics are known the actual design procedure for mass flow is extremely reliable, and it is without doubt the most certain way to a reliable hopper.

There are sometimes other considerations which would lead to a preference for mass flow discharge anyway, principally:-

However, setting those aside and looking at the problem purely from the point of view of reliable discharge, mass flow really comes into its own when dealing with materials which have a significant gain in strength with time. By disturbing the whole contents every time some material is discharged, and giving a “FIFO” discharge, such materials are handled far more effectively than any discharge aid on a core flow hopper ever could. In fact with highly time- dependent materials, it is probably futile to spend any significant amount of time trying out discharge aids. A decision to convert to mass flow will probably be the most cost-effective solution in the long term, even though it usually means cutting the cone off the hopper and fitting a new one, together with losing some vessel capacity to give the steeper cone walls needed.

There are two principal criticisms often levelled at mass flow:-

In practice, both of these can be overcome very effectively using “plane flow” (wedge-shaped) converging sections which do not require to be so steep, and are more tolerant of changes in bulk solid flow properties. One issue which is critical to obtaining mass flow is the interfacing of the feeder at the bottom of the cone; this must allow flow to take place right across the outlet area, which requires a degree of care in selection and interfacing of the feeder. More details of all these issues, together with a detailed analysis of mass flow, can be found in reference (1).

It will of course be appreciated that converting an existing vessel to mass flow can be an expensive exercise (often more costly than fitting discharge aids). However, engineering it into a new vessel is relatively cheap, and it is a very low maintenance option - for this reason it is especially worth looking at for new vessels, particularly for highly time-dependent materials as described above.

The ultimate limitation on mass flow is when the bulk solid is so poorly flowing as to require wall slopes near to vertical; in such cases a full-live-bottom with a mechanical discharger the width of the silo is indicated, as described in the section on mechanical devices.

5.2 “Low-friction” linings

Another way of giving gravity a helping hand is to reduce the amount of work it has to do on the bulk solid during discharge, by reducing the friction between the bulk solid and the hopper wall. Where a hopper is “nearly there” in giving mostly quite reliable flow, this can sometimes be an option, however the choice of lining material is not as straightforward as some vendors of linings would make out.

To take some examples, ultra-high-molecular-weight polyethylenes can be very good for some bulk solids (especially damp or wet ones) but bad for others (hard, angular ones); however the precise grade of polyethylene can make a difference and the grade which is best for some bulk solids will not be the best for others. In the same way, stainless steel can be very good for some bulk solids (not because it is inherently smoother than carbon steel, but because it doesn’t rust and become rough when no flow is occurring) - however, choosing the grade of surface finish is extremely important as a mill finish (No. 1 finish) stainless is rougher than a mill finish carbon steel!

The important point is that to choose a “low friction lining” sensibly, some friction tests with the bulk solid against some different lining options are required. Fortunately the cost of wall friction testing alone is trivial compared with the cost of lining even a modest sized hopper, making it an economic exercise.

A word of warning is in order at this point however, regarding the limits of low friction linings; as stated above, they are at their best with “nearly there” hoppers. If a hopper is nearly mass flow, reducing friction will make it mass flow, likewise if it is firmly in the core flow region but almost self-drains then the lining will aid discharge of the last part of the contents. Remember, however, that installing a lining will reduce the transmission of vibration from the outer wall, thus reducing the effectiveness of any external vibrators.

5.3 Inserts

It seems strange to suggest that putting something in the way of the flow channel can actually improve flow, yet in some cases this can be so. The simplest insert is a plain “Chinese hat” suspended in the hopper cone above the outlet, reducing the consolidation pressure on the bulk solid near the outlet and hence making it more free-flowing. More sophisticated is a cone within the hopper cone and the same way up, but with walls somewhat steeper; this can promote mass flow in cones which otherwise would not mass flow. Other insert shapes have been used and shown to be useful.

However the reality of using inserts is that whilst they are often useful to improve the flow pattern in a bin discharging a fairly free-flowing material, they are of limited use with cohesive materials. Both academic research, and practical experience, have a long way to go before the use of inserts can be recognised as anything like a reliable solution to problems of unreliable discharge.


It is surprising how many cases actually offer the possibility of changing the flow properties of the bulk solid to ease a discharge problem in a hopper. In the food industries it is very common to add a “flow additive” to a product for retail sale in order to render it more freel flowing, thus giving the consumer an easier material to handle and also easing problems in packaging machinery etc. Salt, grated cheese, flavourings etc. are often treated in this way and although the additives are quite wide-ranging, many act in the same way - to provide a coating of small, hard particles on the surfaces of the softer main particles, preventing the main particles from touching and sticking together. The levels of addition and distribution of the fine “flow additive” need to be very carefully controlled to get the best effect, and any chemical effects of the contamination caused by the flow additives must be considered.

Another approach is to control the moisture content. For example, sugar is “conditioned” (a slow, gentle but very searching drying process) to a low moisture content to prevent it from caking in storage. A further approach is to granulate the material (by spray drying, pelletising etc.) to reduce its surface area, thereby reducing its cohesive strength.

All these approaches are known technology, however their utility is usually dictated by the context. For example, if supplying a poorly flowing powder of high value to many customers who then have trouble in handling it, it will be economic for the producer to improve the flow characteristics of the powder. Likewise if reclaiming a blend of low-value mineral from a coarse stockpile, mixed with fines from screening together with ultra-fines settled from a lagoon, it may be worthwhile dumping the ultra-fines instead of reclaiming them, to make the balance of the reclaimed material easier to handle. By contrast, if the problem relates to one hopper in a process plant where the bulk solid is quite closely defined, it will probably be better to adjust the hopper to suit the bulk solid.


From the above it will be clear that the choice of approach to improving flow in hoppers is very much dictated by the circumstances. To sum up, the following table may be useful to indicate what approaches have proved, in the experience of the author, to be most successful in which circumstances:-



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The two-day event on 12th & 13th October 2021 has a packed programme of inspiring speakers planned to deliver insights on topical technical issues and pending projects.

The 2020 winter edition of the SHAPA Supplement has now been released

With articles and information from across the industry, the new SHAPA Supplement is a must read to find out whats positive about our industry, open up the link today and keep upto date

2021 Solids Handling Industry Awards are NOW OPEN

The Solids Handling & Processing Association (SHAPA) are delighted to announce that the annual Solids Handling Awards to promote success and achievement across our collective industries, are now open to all companies registered in UK, whether SHAPA members or not, who are directly involved in the solids handling and processing industry. This exciting opportunity will comprise awards in four categories: the Innovation Award, the Export Award, the Newcomer Award and the SHAPA Company of the Year Award. The awards are open for applications from the 1st December 2020 the closing date for all entries is 28th February 2021for more information check out the link

Automation the next step

While organisations have had to realign their products and services to meet the restrictions imposed by the Covid 19 pandemic many have been faced with also having to quickly automate their systems and procedures to cope with the uncertainty in the labour market due to the continual changes in guidance from the authorities. One of the main ways to bring automation into the workplace is to enhance your existing control systems...

New Technical paper added - ATEX Fan Guide

ATEX fans are fans designed for use in potentially explosive atmospheres and are governed by EU Directive 2014/34/EU. This Directive is intended to increase safety by using a logical risk identification and mitigation method for design manufacture and use...

Returning to Normal

With the total lockdown released by the UK government and being replaced with a more targeted approach, UK and European organisations are starting to get back to working more productively. However, as the overall situation has not yet stabilised with new Covid spikes being found across Europe and the deepening crisis in the Americas, Middle East and India, exporting and importing is going to be significantly different going forward...


It is well established that the SHAPA membership comprises many exceptional companies in bulk materials handling and processing, their combined experience and knowledge amounting to a few centuries. All are merely a few “clicks” away on the SHAPA website www.shapa.co.uk . This is an invaluable resource for all project engineers and specifiers engaged in new projects, updating plant and installations, or simply looking for life extending efficient maintenance.
This leading resource is continually evolving with new technical papers being added all the time...

Zooming around the UK

With the lockdown starting to be released in the UK, Europe and the wider world companies are starting to get back to working productively. However, things are looking different going forward. With a vaccine that may be six to eighteen months away or not at all if you read some scientific journals new ways of working are needed to ensure that we continue to be profitable going forward.

Site visits, surveys and inspections in the wake of Covid-19 restrictions

The long term impact of the Covid-19 pandemic is looking to be widespread and lingering. With the repercussions of lock down, social distancing and furloughing staff likely to affect every industry in very different and unexpected ways...

SHAPA teams up with the LEV INDUSTRY FORUM

SHAPA as an integeral part of the LEV Industry Forum - Competency Working Group have together produced a LEV knowledge guidance matrix for key roles in the LEV industry highlighting the requirements for each role and where to find the appropriate information needed to fulfil the role. further information can be found on the The Chartered Institution of Building Services Engineers ( cibse) website link

SHAPA announces the winners of the 2020 Solids Handling Awards

This year the Solids Handling Industry Award Ceremony has been held using an online Zoom Platform, showing that despite the lockdown and the changes in working practices the SHAPA community continues to work together to develop new and exciting products, export all over the world, develop our young people and celebrate the successes of our industry. The winners of the 2020 Solids handing Industry awards are:-.....

Rob Berry

It is with great sadness that we report the death of our much loved and respected colleague and friend Dr Rob Berry after suffering a long battle with cancer. He will be remembered by the bulk materials handling industry for his great expertise in powder flowability and by his friends and colleagues for his kindness, patience and humour...

A message from Theo our Arkwright Student

I am trying to make the most of these difficult times by staying active and encouraging a positive mindset. Given my school has now closed, I will continue to to try to make the most of my education, and keep up to date with work my school have been providing me with online.
As an Arkwright scholar, and am taking advantage of any extra time to learn about engineering, and keep up to date with any new advancements made in engineering.
I hope everybody keeps well

SHAPA Announces the shortlist for the 2020 Solids Handling Industry Awards

2020 has once again been an excellent year for the Solids Handling industry with many successes in all areas of solids and material handling, all of the nominations for these awards show the strength and depth of the solids handling industry and we thank all the nominees for sharing their own successes...

Coronavirus letter from Shapa Chairman

Following the recent announcements regarding the current Coronavirus and its implications on travel and meetings, the SHAPA council have agreed to postpone the Annual AGM and Awards Dinner for this year until we feel that the situation has come under control and the advice from the government has been relaxed. We also intend to cancel face to face meetings until the advice changes, we are sure that within your own businesses you are taking similar precautions....

Annual Awards Dinner Cancelled

Due to the current situation regarding the Coronavirus outbreak, the council have agreed to cancel the Awards dinner which was due to take place on the 22nd April. arrangements are being made to carry on with the Awards presentations and AGM further details to follow

Health of the nation

The need for solid health and safety systems, procedures and practices are more important than ever as we move out of the European and Customs union into the wider world sometimes using the World Trade Organisation rules for the global market. While it is hoped that in time that the UK will negotiate reciprocal trade agreements with many of our trading partners throughout the world, there is a need to make sure we do not miss out on opportunities during this period of change....

Solids Handling Industry Awards

The 2020 Solids Handling Industry Awards Dinner is being held at the Brookland Museum in Weybridge on the 22nd April 2020. Dont miss out on the prestegious Black tie dinner with two free places for members, download the booking form today and guarantee your place. Download the booking form today  

12th Digital Marketing workshop details launched

Shapa are holding the 12 th Digital Marketing Workshop, this highly successful event helps keep pace with the latest developments in Digital marketing. The event is exclusively for member companies and covers, whats new in Digital Marketing, Google analytics, Online advertising, and your Digital Marketing Toolbox to name but a few of the areas to be covered...


Grinding out the right solution

Size reduction is one of the oldest processes known to man from before time when grains were pounded and ground to make flour. Size reduction machines still mill harvested materials but also a vast variety of other food, chemical, pharmaceutical and mined materials too...

Merry Christmas


2020 Solids Handling Industry Awards are now Open

The Solids Handling & Processing Association (SHAPA) are delighted to announce that the annual Solids Handling Awards to promote success and achievement across our collective industries,  are now open to all companies registered in UK, whether SHAPA members or not, who are directly involved in the solids handling and processing industry. This exciting opportunity will comprise awards in four categories: the Innovation Award, the Export Award, the Newcomer Award and the SHAPA Company of the Year Award...

Shapa Welcomes their new Arkwright Student

SHAPA Council Member James Podevyn and Ian Birkinshaw attended the Arkwright scholarship presentation event in Edinburgh to welcome our new Arkwright scholar Theo Cains to the Association


Explosion Safety Revisited

Over the past months The SHAPA technical committee have reviewed the information available and updated the advice given in the two publications within the SHAPA technical library available at https://www.shapa.co.uk/technical.php these being Compliance with Legislation Implementing the Atex directive and an Atex PowerPoint presentation....

Dust extraction systems

Wherever solid particulates are handled, processed, stored or are created, as a bi product of a process such as machining or finishing, dust is usually generated.
This dust needs to be controlled to prevent risks to health and environmental damage...

The New Shapa Supplement Now Available

Always in Control

Industry 4.0 is reported to be the next major revolution in industrialisation. The main focus is to take all the individual processes and systems that are used in manufacturing to manage and control production, and import them into a cloud-based system This allows the workflow, product changes and the management of each and every individual machine or a series of machines can be controlled remotely...

Sucess for Georgina

Georgina Edwards, SHAPAs Arkwright Scholar has sucessfully passed her A levels with flying colours and is now bound for Loughborough University to continue on with her studies. We wish her well in the future and pass on our congratulations and best wishes.

Shapa and Santander Trade Mission

Shapa has been working with Santander to help organise a World Food India 19 trade mission to take place on the 1- 4th November 2019, for more information please download the flyer here 

Materials in Motion

Most products at some stage of their life during production or manufacture, utilise materials in powder or granulated form. This is where the challenge can be for the designers of equipment and processes to move these types of materials from place to place, horizontally, vertically or somewhere in between. The conveyor or elevator designer must consider a multitude of parameters, probably more than twenty in their pursuit of the most effective solution....

SHAPA Announces the winners of the 2019 Solids Handling Industry Awards

Open and Shut Case

There are many types of valves used within the bulk handling industry for controlling, conditioning or diverting the flow of powders or liquids. There are three main types of valves, these being shut off, diverter and rotary valves.

Solids Handling Awards - Shortlist

2019 has once again been an excellent year for the Solids Handling industry with many successes in all areas of solids and material handling, these successes have produced a strong shortlist for each of this years award categories. This year the award categories are, Solids Handling Export Award, Solids Handling Innovation Award, Solids Handling Newcomer Award and Solids Handling Company of the year award. The shortlisted nominations for each award category are:-

Solids Handling Industry Awards Dinner

Bookings are now being taken for the 2019 Solids Handling Industry Awards evening. This year the awards are being held at the Royal Armouries in Leeds on the evening of the 8th May. Once again one delegate from each member company can attend the AGM and dinner free of charge, with additional delegates paying a nominal fee to cover the evening meal.   These awards are going from strength and this years nominations have been among the best that we have received. After the award presentations we will be entertained by local comedian Brian Newbold who comes highly recommended. There are still places available for this chance to celebrate the best in our industry and network with your friends and colleagues. Once again the dinner is open to members, their spouses, partners, customers and suppliers. So don’t miss out on this great opportunity just complete the booking form to guarantee your place   Please follow the link to download the AGM and Awards dinner booking form

Shapa Celebrates International Women's Day

SHAPA is proud to be involved with International Women’s Day on the 8th March to celebrate and promote successes in the world of Solids Handling and Processing. International Women’s Day provides a spotlight to showcase the commitment to women's equality, launch new initiatives and action, celebrate women's achievements, raise awareness, highlight gender parity gains and more.

See the Full story here

Magnetic Attraction

Most common manufacturing applications have a requirement for the use of Industrial metal detection systems for the inspection of bulk powders, granular or free flowing products. This is common place within the majority of most Food, Pharmaceutical and O.E.M applications where metal detection systems are used as part of a quality control programme.

Getting the Mix Right

The terminology ‘mixing’ and ‘blending’ is often grouped together as the same process, technically they are slightly different. The process of blending is the homogenous distribution of differing materials and is usually a relatively gentle process. Whereas mixing is usually a more aggressive process involving the combining of materials through the beating or stirring of the contents within a static vessel...

Safety of Machinery and CE Marking for Machinery workshop details launched

SHAPA are holding the workshop to give designers of machinery the knowledge and tools to design safe machinery in accordance with current Machinery and associated directives. it will also include a section on any implications as a result of the brexit agreements...

11th Digital Marketing workshop details launched

Shapa are holding the 11 th Digital Marketing Workshop, this highly successful event helps keep pace with the latest developments in Digital marketing. The event is exclusively for member companies and covers, whats new in Digital Marketing, Google analytics, Online advertising, and your Digital Marketing Toolbox to name but a few of the areas to be covered...

16th Jan 2019 Shapa General Meeting - Agenda

Agenda for the SHAPA General Meeting- Wednesday 16th January 2019 at 10:00 am

The George Hotel
WS13 6PR

1. Apologies for Absence
2. Minutes and Matters Arising
3. General Secretary’s and Membership Report
4. Chairman’s Report
5. Technical Committee Report
6. Marketing Committee Report

7. Coffee

8. Presentations

    Imagineering – A New project
    Bob Shanks - Imagineering Foundation

    Maximising your innovations
    Tony Cassidy- The MPA Group

9.   AOB – and dates of next Meetings
10. Buffet lunch

Merry Christmas

Christmas SHAPA

2019 Solids Handling Industry Awards are now open for nominations

Solids Handling Awards 2019

The Solids Handling & Processing Association (SHAPA) are delighted to announce that the annual Solids Handling Awards to promote success and achievement across our collective industries, that are open to all companies registered in UK, whether SHAPA members or not, who are directly involved in the solids handling and processing industry...

2019 Solids Handling Industry Awards open on the 1st December 2018

The 2019 Solids handling Industry awards are oepn form the 1st December 2018, the Catagories are Innovation, Export, Newcomer and Company of the Year. This year the Awards Ceremony will be held at the Royal Armories in leeds on the 8th May 2019. Don't miss out on these prestigious awards download the application form today.Tthe closing date for entries is the 28th Feburary 2019. 


As this year’s exhibition season is now ending it is very heartening to see that despite competition from other media, internet and so on, the physical exhibition remains an important marketing tool. Three of the exhibitions held this autumn, Recycled Waste Management (RWM), PPMA and BULKEX18 for Bulk Handling equipment providers and processors demonstrated the wide reach of our remit, from raw material production, via processing and manufacture, packaging and distribution through to final recycling and waste disposal...

Digital Marketing Workshop 2019

The date for the next Digital Marketing workshop has been announced as the 26th March 2019 at the East Midlands Hilton Hotel more details to follow.

Shapa General Meeting 24th October George Hotel Lichfield

IIntroduction to Bulk Handling Workshop

Shapa is running a new Introduction to Bulk Handling Workshop to be held at Nestle in york on the 4th December 2018. This workshop is specifically designed to take some of the mystique out of solids and bulk handling...The course which
is aimed at those who have just joined the bulk handling community and those who already work in the bulk handling industry in sales, marketing, accounts and operations etc. who feel that they need a deeper understanding of how
their products and services fit into the wider environment....

Better by Design

It is well known that an elegant design that works reliably is devoid of baulking obstructions and ambiguities and is simple to understand and operate. It is, of necessity, the result of ingenuity, experience, good applied science and engineering....

Safe to Breathe

For more than a century there have been efforts to improve air quality in the working environment, both in enclosed factories and other industrial areas. Even with scant knowledge of respiratory diseases it had been clear that people were more productive in a cleaner and better environment....


SHAPA announces the award catagories for 2019

The catagories for the 2019 Solids Handling Industry Awards have been Finalised, these are, Innovation, Export, Newcomer and Company of the Year. The presentation of the awards will be on the 30th April 2019. A venue will be announced shortly 


Hoppers, Silos and Storage Solutions

It used to be that all you needed to store your materials was a large area where your product could be piled high on top of its self out in the open air. As time has moved forward the need for more sophisticated storage solutions are required in order to safely store the ever-increasing range of bulk solid materials with their differing properties .....

SHAPA July General Meeting

The next SHAPA General meeting is on the 4th July at the George Hotel Lichfield download the agenda here


And the Winners of the 2018 Solids Handling Awards are:

Shapa's Arkwright Student posts her latest Blog

What an incredible experience competing at the National Finals of the F1 in Schools competition. Throughout 2 days of intense competition and jam packed action, Ginetta Racing Edu earnt the ‘Team Sponsorship and Marketing’ award, as well as being nominated for the ‘Pit Display’ and ‘Innovation’ awards, and having the second fastest car! Read the full article here

Promoting Success

Since time immemorial progress has been driven by innovation and invention and the desire to continually improve and better ones self. The desire to learn, improve and push at boundaries is an integral part of our nature. Whilst innovation in solids handling and processing seldom hits the headlines, it nonetheless drives the machinery of progress across an enormous range of industries.....


Shapa Announces the 2018 Solids Handling Shortlisted finalists

2018 has been an excellent year for the Solids Handling industry with many successes in all areas of Solids Handling, these successes have produced a strong shortlist for each of the award categories. this year the sortlisted entrys are ....

10th Anniversary Digital Marketing Workshop

Details of the 10th annual digital marketing workshop have been released,download the flyer for the event here and a booking form to make sure you do not miss out on this vital workshop which will give you the tools to improve your digital marketing profile

Health of the Nation

The need for solid health and safety systems procedures and practices is more important than ever as we move out of the European and customs union into World Trade Organisation rules for the global market read more here....

Only three weeks left to enter the 2018 Solids Handling industry awards - dont miss out

Learning to succeed

Many companies are founded on the back of an innovative idea by forward thinking people skilled in design, engineering, project management, marketing or other discipline. Whilst still small, the skills required to operate all aspects may possibly be gained by the founder. In former, less complicated times this may have been true as the firm expanded, but the pace of change of technology, standards and legislation as well as in marketing and particularly in financial accounting necessitates constant learning and improvement. The huge range of applications and processes served by our industry just adds to this challenge.....

Shapa's Arkwright Student posts her second Blog

Reaching the end of a very busy Christmas term, we have lots to look back on, such as assisting backstage with the school play and Christmas concert, as well as designing and manufacturing the F1 in Schools Car....

SHAPA January Meeting

The next General meeting will be held on the 24th January at the George Hotel in Lichfield starting at 10:00
Find out about OEE and GDPR, along with all the usual networking oppertunities.
for more details email Ian at info@shapa.co.uk and download the agenda

Applications are invited for the 2018 Solids Handling Industry awards

Shapa has launched the 2018 Solids Handling Industry awards, these awards are now open to all UK registered member and non member companies and institutions operating in the Solids Handling and Processing Industry. Application forms will be  available direct from the website from 01/12/2017 and winners will be announced and presented at the awards ceremony in the evening of 17th April 2018 more information is available in the link

2018 Solids Handling Industry Awards

Details of the award catagories and award launch date have been announced, for further information follow the link

Solids Dortmund 2018

Details have been released regarding the international Solids Handling show to be held in Dortmund on the 7th and 8th November 2018, for more information please follow the  link

CHoPS 2018

**Abstracts deadline extended to 22-12-17 ** for more information follow the link

Financial Awarness Training

This course has been especially designed for Shapa members and will include content specifically related to our industry

Who should attend ?
Anyone involved in driving their business forward e.g Managing Directors, Directors/Managers & Account Managers etc , whatever their level of financial knowledge. The workshop is designed to enable everyone to take away practical tips and strategic insight suitable to their skills and experience, whether you are a beginner, intermediate or advanced. So join us for and inspiring and enjoyable day out.

Download the detailedinformation and a booking form,today

If you can return these back to info@shapa.co.uk  as soon as possible so I can make the necessary arrangements and  if you feel that this course would help with someone in your close supply chain please feel free to include them.