Shane,

The normal vertical placement of the tail pulley is such that the top of the tail pulley is in-line with the top of the horizontal center can of the troughing idlers. This definition will correspond with your ?at trough height? term.

Placing the tail pulley at a half-trough position means that the top of the pulley is in-line with a point halfway between the top of the horizontal idler and the top tip of the angled idlers. In practice, most of the elevated tail pulleys are not set that high.

Typically, the half-trough positioning has been used as a method to shorten the transition zone length. That is, the ?advantage? of the half-trough positioning is that it saves space. The disadvantages of the half-trough positioning are that it increases wear on the belt and pulley, and can make the belt training more difficult.

I believe that half-trough positioning of tail pulleys should not be used, unless it is absolutely necessary and the operator is fully aware of the extra ongoing maintenance costs involved.

Regards, ■

Hello Shane,

Mr. Dave Miller has already given the explanation and reply. Generally one keeps the pulley top point in line with the belt carrying run reference line. However in some belt conveyor layout sometimes there is a constraint on available space i.e. there is not adequate distance between feed point and tail pulley. In this situation one can raise the pulley level with reference to belt line and it will need lesser transition distance.

The raising of the pulley creates new distribution of belt tension within the carcass. So, it is to be done based on specific calculations such that the tensions remain within the safety limits and also belt behaves properly in the transition zone.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

One of the major problems we have found with the half trough design, is the sealing of the load zone. In the unloaded condition, the belt does not rest in the trough in the load zone. The sealing systems are adjusted to the unloaded belt. Then when the belt is loaded, the belt now rests in the trough fully, and moves away from the sealing system.

If space for the transition distance is a problem, we have made a load zone that transitions from the the tail pulley to the fully troughed position over the entire length of the load zone. This is done by using adjustable idlers and gradually changing the belt from flat to trough. ■