This can be done. You must have a reasonable knowledge of its consequences when the drive(s) are somewhat remote to the head.

The belt can store a lot of potential energy between head pulley and drives depending on belt length between head pulley and drive(s), belt modulus, mass, idler details, and drive inertia dynamics.

Once the holdback locks, at zero speed, there can be substantial energy stored in belt stretch between head pulley and drive(s) that must release in a reverse motion or rotation of the drives like a yo-yo. ■

A second point and third point:

2) it also depends on the type of take-up - gravity will yo-yo which leads to point 3.

3) when the yo-yo effect occurs you must have knowledge of the dynamics that reduces the slack side holdback tension as the drive reverse rotation drops the belt tension between head holdback and drives.

This last point suggests that there may be holdback head pulley belt slippage and its consequences. ■

Most likely will not overstress the belt splices, but can introduce some bad slippage and its aftermath. ■

dear sir

Please ensure head pulley is lagged ang grooved

A R SINGH ■

Hello Sterling

I had numerous arguments with Clarence Seaton many years ago on this topic. He was (is?) the President of Marland holdbacks and always claimed that you must only put in a holdback on the head pulley remote from the drives, which is rated at the full installed motor torque.

His explanation was that if the tail gets jammed, and the drives trip out, then all the torque goes into the head pulley being restrained by the holdback.

He also sells holdbacks and therefore the bigger the holdback the better for him.

My argument was that there is far less wrap on the single head pulley than on the multiple drive pulleys so this cannot be true.

What I used to do for such cases, for example on long conveyors feeding silos where the belt just tends to roll back a bit, is put a holdback suited for the rollback duty, on an unlagged head pulley (clean side of the belt).

This works very well, but nowadays I tend to put a slightly larger holdback on the spare extension on the secondary drive pulley.

Normally two primary drives and one secondary drive with H/B.

At Rossing Uranium where we have put in an overland conveyor to carry the previously pumped tails to the dam area, there is a fairly big capacity 1km length and considerable lift.

We have 3 drives and one holdback on the secondary pulley. For safety sake though, I have put a high speed holdback on the gearbox of the secondary drive pulley as well. This is a very cheap back up and works well.

LSL Tekpro ■

Hi there Matt..

Interested to read your input on the holdbacks.. but the use of two different holdbacks on the one secondary is working well in practice.

For the aborted start, I find that most of the dynamics have settled down before the conveyors finally draw to a halt, provided the start factor is sufficiently low.

Cheers

LSL Tekpro ■