Pipe conveyors: when a closed belt earns its cost

A pipe conveyor is an ordinary belt conveyor for the first few metres and the last few. In between, the belt is rolled into a tube, and everything that makes an open belt cheap and everything that makes it a nuisance changes at once. The question is whether this route has the problems a closed belt solves.

What is a pipe conveyor?

The belt is loaded flat or in a shallow trough at the tail. Over a transition length, idler panels — six rolls in a hexagon — fold it progressively until the edges overlap on top and the material is enclosed in a tube. The panels hold that shape through horizontal and vertical curves and open the belt again before the head pulley. The return strand is rolled up too, dirty side inward, so it sheds no carry-back and can carry a second material back. The belt itself is built stiff enough across its width to hold the tube.

When does it earn its cost?

• Dust and the environment — enclosed from loading to discharge: no spillage along the run, no wind losses, no wash-off in rain. For fine, dusty materials such as fly ash, enclosure is the specification.
• Curves that remove transfer towers — a pipe belt turns corners horizontally and vertically, so three open belts and two transfers become one machine. Every transfer removed is a chute, a dust source, a drive and a structure; the transfer point note explains what each costs to get right.
• Steeper inclines — with the material held in the tube, commonly quoted angles reach around 30°, against the high teens for an open belt.
• Spillage-sensitive routes — over public roads, water, railways or other plant, where a spill is an incident rather than housekeeping.
• Weather — long outdoor routes where covers on an open belt would be a maintenance item of their own.

What does it cost you in return?

• Belt and drive — a purpose-built belt costs more, and forming and holding the tube adds rolling resistance, so drive power for the same duty is higher.
• Idlers — six rolls per panel instead of three, at a closer pitch: more to buy, more to inspect, and a roll change in a confined frame.
• Curve radii — commonly quoted as a few hundred times the pipe diameter, so even a modest pipe needs tens of metres to turn; a tight site loses the main advantage.
• Lump size — limited to a fraction of the pipe diameter, so the pipe is often sized by the lumps rather than the tonnage; the lump the material never contains opens the overlap.
• Fill ratio — the tube is designed part-full; overfilling makes the belt bulge, rotate and spill inside the panels.
• Rotation and the overlap — the belt must not twist in the panels; belt stiffness, panel alignment, curve design and uniform loading all contribute.
• Transitions — closing and opening the belt each need a run commonly quoted as several tens of pipe diameters, which cannot be shortened to fit a building.

The comparison of conveyor types puts the pipe conveyor beside the open belt, screw, airslide and elevator on the same duty; both belts are part of our conveying systems work, and the route survey is where the decision is made.