If you understand the functioning of fluid couplings and variable frequency drives you'll understand that you only use one not both. ■

Hello all

VSD's are good for long smooth start up times whilst also being motor friendly (electrical soft starts are not motor friendly and have no good track record on multiple drives)

Fluid couplings are the answer but only for low inertia inclined conveyors or overland generally less than about 4km due to the start up time limitation before they cook, hence the scoops and drain couplings, which have external oil cooling.

There was a fad where they combined elecrical soft start with fluid couplings. Fortunately this did not last long, but unfortunately the fad changed to putting VSD's on just about everything.

There has been lots of mis-information about the "savings" from using VSD's

It actually looks like there is more energy loss at the VSD unit itself than the 3% loss you get in a fluid coupling. Hence the massive air conditioning units for the rooms housing the VSD's

Then you have to pay for a very clever person to sort them out (fluid couplings just need oil!)

This man costs money, and so does the VSD which will have to be replace a few times over the life of the conveyor, just like I have to replace my laptop! Work it out... the overall costs using VSD's is huge.

And then there is all this mis-information about saving power by running the belt full whatever the capacity by using the VSD.

According to my research, this does not apply to any conveyor less than about a kilometre long, as the effect of sag on lower tension conveyors is huge and causes excessive power loss, and the idler imprint load drag increases exponentially as the load increases. So why on earth keep it maximum at all times!

I notice that when I was in Australia on a recent project, the tendancy now is to not go the VSD route, except where it is of actual benefit. I wonder how long it will be before it is generally taken that VSD's are no longer the flavour of the month.

Watch this space..

Anyway VSD plus fluid coupling...nnnope..

Cheers

LSL Tekpro ■

Check this type of variable speed Clutch(Brake Type) & Gearbox drive system. These units in Huo Ji Tu(Mongolia) are the drives I check & commissioned for the drift conveyors in 1998. The drive is a compact and extremely reliable and are much cheaper in the initial purchase when all the electrical componentry and cabling is included, about 20% cheaper than any other comparative drive unit as well as a low ongoing maintenance cost in comparison with others. I highly recommend these drive units provided the LCDs (Lowest Common Denominator) who service them are well trained to do the correct thing. At a particular mine that had a big turnover of personnel including maintenance crews. One untrained maintenance person used the wrong oil which caused havoc with one drive unit and as such, a gearbox was serviced with gear oil instead of the correct hydraulic oil of specified grade. Apart from that incident, these Reliance-Dodge CST's are one of the leading units to look after conveyors systems in terms of gentle operating conditions on the system from Tail to Jib pulley and all bits in-between and longevity of reliable ongoing service.

http://www.mromagazine.com/issues/st...int%20Archives ■

The VFD drive control has come a long way and is now economical and very effective in controlling long smooth starts and stops and can run at varied continuous speeds. A fix fill fluid coupling is good for limiting max torque and inrush current during starting and they can be used on multiple drives to affect good load sharing. The idea of using both at a single conveyor is absurd but reluctantly had the occasion to participate in such an absurdity. We built one of our sandwich belt high angle conveyors by licensing a foreign partner who actually supplied it. Without our agreement that partner used a single VFD to control the DSI Snake conveyor speed at both belts and fluid couplings (one at each drive) to affect load sharing between the drives. The latter pretty well precluded the benefit of the former. The first time that they slowed the belt speed appreciably they overheated and blew the plug of a coupling. This was inevitable and a terrible idea.

Joe Dos Santos ■