The choice between a screw conveyor and pneumatic conveying for cement depends on the complete transfer duty. A screw moves powder mechanically in a tube or trough; a pneumatic system uses a gas flow and pressure difference through a pipeline. Distance, elevation, routing, feed conditions, containment and operating cost must be assessed together.
VOGO supplies tubular cement screw conveyors. That does not establish that screws win every application. Pneumatic systems can be appropriate for long or complex routes, while a screw may offer a compact local connection. Compare fully specified alternatives rather than catalog labels.
How each system moves cement
A screw’s rotating flight moves material by contact with the flight and housing. Capacity depends on geometry, speed, fill, slip, inclination and material condition. It is not a perfectly sealed positive-displacement pump delivering an invariant volume or mass per revolution. A flood-loaded inlet under a silo needs feeder design, while a control-fed conveyor receives a limited flow from another device. The KWS engineering guides distinguish these duties.
Pneumatic systems can use pressure or vacuum, with an appropriately selected blower, compressor or other gas source. Feed devices can include rotary valves, pressure vessels or specially designed screw pumps. The receiver separates solids and gas using equipment selected for the particle distribution and emission requirement; a cyclone alone may not meet a fine-cement dust target. Dilute phase suspends particles, while dense phase includes several flow modes, not only discrete plugs. Coperion documents both methods and emphasizes material-specific selection.
| Principle | Screw conveyor | Pneumatic conveyor |
|---|---|---|
| Transport | Rotating flight in tube or trough | Gas-driven transport through pipe |
| Flow | Depends on geometry, filling and slip | Suspension or a suitable dense-phase mode |
| Introduction | Control-fed conveyor or engineered flood-loaded feeder | Feed device matched to pressure and powder |
| Discharge | Outlet into a suitable receiver | Gas/solid separation and appropriate filtration |
These differences affect every cost and interface, so the scope must include more than the conveying body.
Side-by-side comparison for cement
| Factor | Screw conveyor | Pneumatic conveyor |
|---|---|---|
| Distance | Often evaluated for local transfers; no universal 3–30 m band | Can suit longer routes, subject to pressure and material limits |
| Routing | Usually straight; changes may need another machine | Bends and lifts possible, with pressure-loss and wear consequences |
| Short-route investment | May be lower for a simple complete installation | Includes gas supply, feeding, receiver, filtration and controls |
| Energy per tonne | Mechanical duty plus auxiliaries | Gas generation, feeding and filtration; compare actual system input |
| Maintenance | Flights, bearings, seals, shaft and drive | Gas source, valves, filters, pipes and bends |
| Containment | Seals and joints must meet a defined target | Pipe and receiver must meet a defined target; leaks remain possible |
| Product change | Contact and shear can alter fragile material | Velocity and impacts can cause attrition; mode selection matters |
| Multiple points | Multiple inlets or outlets can be engineered | Valves and feed controls can serve multiple routes |
| Damp or sticky material | May need special design; cement can cake or set | Can deposit or plug; assess material and process limits |
Use the table as a screening tool. Neither cost nor product quality can be established from technology name alone.
Capital, operating and ownership costs
Capital cost
A short silo-to-weigh-hopper screw may need fewer components than a complete pneumatic system. Include supports, drives, guarding, isolation, controls and venting on both sides. Do not compare a bare screw price with an installed pneumatic package. Generic dollar-per-foot ranges without matching throughput, scope, location and date are not a sound quotation basis.
Longer routes may require multiple screws, transfers and structures, while a pneumatic line may avoid some of those interfaces. It still needs pressure-drop calculation, suitable pipe supports, bends and possibly different gas-generation or feeding equipment. There is no universal crossover distance at which the cheaper system changes.
Energy cost
A screw can have an energy advantage in some short transfers, but verify electrical input per delivered tonne at the same duty. Include the pneumatic gas source, air treatment, feeder and filter cleaning, and the screw’s extraction or purge where used. An unsupported value such as 8–15 kW per running metre should not be used to size or cost a pneumatic plant.
Dense-phase operation may reduce gas velocity and wear for a suitable powder, but it does not automatically guarantee lower total energy than every dilute-phase system. Use the proposed pressure, gas rate, efficiency, cycle and throughput. Annual energy cost depends on load and operating hours; compare 2,000 and 200 hours as different utilization scenarios rather than mixing them in one quotation.
Maintenance cost
For screws, record flight and housing wear, bearings, seals, couplings and gearbox service. Wear is not always visible without isolation and access, nor perfectly predictable. For pneumatic systems, include gas-source service, valves, filters, pipe thickness and elbow inspections. Fewer rotating parts in the pipeline do not mean a maintenance-free system. Lower velocity can reduce some wear mechanisms but does not eliminate them.
Total cost of ownership
Compare purchase, freight, installation, energy, preventive-maintenance labor, wear parts, unplanned downtime, disposal and residual value over the same period. Initial price is not universally 20–30% of a ten- or fifteen-year total. Use scenario ranges and site data rather than assuming a screw always wins short routes or pneumatic always wins long ones.
The cement screw sizing guide helps organize the mechanical option’s inputs. A pneumatic supplier must calculate its own complete proposal. The TCO guide explains consistent cost boundaries and assumptions.
Layout, distance and site constraints
A straight screw connection can be simple, but routing around columns or between floors may need transfers and more machines. Each transfer adds space, control and containment requirements. Include maintenance withdrawal space and lifting access rather than comparing only the outside diameter.
Pipelines can route around obstacles and serve selected destinations, but bends, rises, diverters and branch states change pressure loss, wear, clearing and control. Multiple pickups do not automatically operate simultaneously at the required rate. Include receiver capacity and the gas-handling equipment’s space.
A 10 m straight transfer and a 200 m route with two bends and a 15 m lift are different duties, not automatic price verdicts. The longer route merits pneumatic evaluation alongside feasible alternatives. The inclination guide describes screw capacity effects; pneumatic lift also has a pressure and energy cost.
Dust control and containment
Both systems need a defined leakage or emission target. A pneumatic line encloses the material and separates conveying gas at the receiver. Positive-pressure leaks can release dust, while a vacuum leak may draw in air and affect performance or contamination. Filter condition, joints and pressure controls matter; a pipeline is not proof of zero emissions.
A tubular screw can limit exposure but still has shaft seals, flanges, hatches and transitions. Coordinate receiver venting, pressure, gaskets and seal geometry. Verify normal and upset states rather than treating enclosure as a containment guarantee.
If the actual material presents an explosion hazard, assess both systems and their connected volumes. Either may require ignition controls and designed protection or isolation. Ordinary process pressure relief is different from explosion venting. Do not claim that explosion-pressure or venting issues apply only to pneumatic systems; use the explosion-risk guide for the evidence needed.
When to evaluate a screw conveyor
A screw deserves consideration when:
- the transfer is short enough for a practical engineered arrangement, rather than an arbitrary 30 m limit;
- the route is straight or an achievable incline;
- a complete local machine offers an attractive installed cost;
- the site has safe access and capability to inspect and replace mechanical wear parts;
- the actual material, including moisture variation, is demonstrated to suit the design;
- a designed screw feeder can combine silo withdrawal with a short onward transfer.
The silo discharge guide explains the feeder interface. Damp cement is not a reason to assume a standard screw will work: hydration and hard deposits can impair both technologies.
When to evaluate pneumatic conveying
Pneumatic conveying deserves consideration when:
- the distance would otherwise require several mechanical transfers;
- obstacles or elevation changes favor a pipeline route;
- multiple sources or destinations can be served by an engineered valve and control arrangement;
- the specified receiver and filtration meet containment needs;
- the pipe route and auxiliary equipment fit the available space;
- product isolation and compatible conveying-gas quality can be demonstrated.
Evaluate dilute and dense phase with representative material data or trials. Reduced velocity may help abrasion and attrition, but dense phase is not a universal default and does not require every powder to behave as a freely flowing granule. Confirm feeding, pressure, clearing, restart and product quality for the selected mode.
A selection decision sequence
- Define maximum and minimum capacity, distance, lift, bends, sources and destinations.
- Characterize density range, moisture, temperature, particle sizes, abrasiveness and flow. Record aerated, settled and consolidated conditions.
- Define emissions, operating pressure, applicable hazardous-area requirements and any special cleanliness conditions.
- Check route feasibility, headroom, supports, access and the number of mechanical transfers.
- Estimate electrical input and annual energy for each complete option at the same load schedule and site tariff.
- Build a lifecycle worksheet including installation, maintenance, wear, downtime and end-of-life treatment.
- Obtain comparable proposals with performance, power, maintenance assumptions, spares and acceptance tests.
State exclusions explicitly. A catalog machine and a turnkey plant cannot be compared fairly until their boundaries match.
Worked scenario: silo to weigh hopper
Assume a required 40 t/h, 6 m horizontal offset and 4 m rise, with an available straight route and operation for 10 h/day on 250 days/year. The straight geometric length is √(6²+4²) ≈ 7.21 m, the angle arctan(4/6) ≈ 33.7°, and scheduled operation 2,500 h/year. These are illustrative inputs, not a verified VOGO installation or low-utilization claim.
A tubular screw is a candidate, but the relatively steep angle requires capacity, fallback, power, loaded-start, feeder and support checks before declaring 40 t/h feasible. Include the weigh-hopper connection and cutoff control, as well as safe bearing and seal access. A catalog diameter alone does not establish output.
A pneumatic alternative needs a suitable feed device, gas source, pipe route, receiver and filtration. A rotary valve is one possible interface, not mandatory for every pressure or dense-phase design. Obtain gas and power requirements and verify the effect of conveying air on weighing and receiver pressure. Compare investment, annual energy, maintenance and accepted performance using actual proposals.
If a second silo is added 80 m away across a driveway, reevaluate the route and operating sequence. A shared pneumatic line may become attractive, but needs source selection, capacity, pressure and clearing checks. It is not automatically achieved by adding one diverter to the original installation.
Hybrid systems
A screw feeder can meter material toward a pneumatic feed device while the pipeline handles the longer route. Coordinate the pressure boundary, feed rate, leakage gas, isolation and interlocks. An ordinary conveyor screw is not a pressure-sealing pneumatic screw pump; Fuller-Kinyon equipment illustrates that the latter is a distinct engineered machine.
A screw can also feed an air-gravity conveyor or bucket elevator. An Airslide-type conveyor fluidizes powder and uses a suitable downward slope; it should not be specified as a zero-slope horizontal transporter merely because it uses air. A bucket elevator provides a separate lifting method with its own feed and containment interfaces.
Assess the complete path. A combination may be appropriate, but every interface adds requirements that must be included in the performance and cost scope.
Common misconceptions
“Pneumatic is always more expensive.” Route, scope, throughput and utilization can change the result. Compare complete proposals and lifecycle assumptions.
“A screw is dust-free because it is enclosed.” Verify seals, joints, pressure and acceptance criteria. The same need for verification applies to pneumatic containment.
“A screw cannot serve a longer route.” Engineered longer systems or multiple units are possible, but support, shaft dynamics, access and transfers matter. Intermediate bearings are not a universal solution to every length.
“Pneumatic systems need no maintenance.” Gas sources, filters, valves, bends and pipelines require inspection and service. Material and operating mode influence wear.
Conclusion
Use a screw’s local mechanical simplicity and a pneumatic system’s routing possibilities as starting points, not predetermined winners. Define the powder and complete path, verify each design’s performance and compare equal cost boundaries. Give VOGO the mechanical duty data and obtain a corresponding pneumatic proposal before choosing on energy, maintenance, containment and lifecycle value.
