V-type Return Idlers for Reversible Conveyors

Posted in: , on 29. Mar. 2007 - 07:48


Can anyone comment on the advantages of using vertical V-type return idlers (2 rolls) over straight returns on a reversible belt conveyor to improve tracking?

The conventional wisdom is that the transverse sag would pull the belt halves towards the centre to counteract any mistracking forces in the outboard directions. Is this true?

Also, I'd reckon the sag would increase Kx but what is the impact on Ky and will there be any additional losses caused by the buckling tendencies on the belt at trough bottom? And how would one quantify these?

Best regards.

Barry Chung

Re: V-Type Return Idlers For Reversible Conveyors

Posted on 29. Mar. 2007 - 11:02


The item that you descibe is a Flexco product. In the U. S. it is called the Rockline RPB1 Belt Positioner. This product was actually created by our Australian subsidiary. It is not located on their web site but you can call them in an hour or two when they open. It is 7 AM over there now. There number is 61-2-9680-3322.

They should have the info that you need. I have never heard questions on tension in the U. S. and elsewhere.

As for the belt buckling, this does not happen if the tool is used properly and the belt is in good working condition.

We have a local representative in Kuala Lumpur also.





Phone: 603-6258-7211

Fax: 603-6251-1644


Re: V-Type Return Idlers For Reversible Conveyors

Posted on 30. Mar. 2007 - 03:07

Dear Mr. Finnegan,

Thank you for your response. I believe the product you are talking about is an auto belt tracker for reversible conveyors. I have used them before and they work wonders when properly installed and maintained. I am talking about the good ones that is, and not those supplied during construction.

But right now, I'm actually seeking to calculate the power requirements for a project and would like to know the additional losses caused by using V-returns rather than straight returns.

I have read on another thread earlier on this issue but the debate was mostly centred on the merits of garlands over conventional idlers. There was no mention of V-returns which I thought was a more logical option. Nevertheless, they did all agree that one should not install auto trackers for reversible belts. Thought this a bit strange though since I've actually seen these work quite effectively before.

Perhaps the same people might like to comment?

Best regards.

Barry Chung

Re: V-Type Return Idlers For Reversible Conveyors

Posted on 18. Apr. 2007 - 01:12

Hi Barry..

You are correct in your assumption that the Vee will help track the belt. This will also hold true for reversible belts, but only if there is no built in forward tilt for the rolls, normaly put in for tracking in one direction only.

As regards the increase in power for the vee's, there is a marginal increase in rotating mass that should be included in your calcuations. The rest (sag effect etc) is negligible, as the vee tends to stiffen the belt in the vertical direction, actually reducing the sag a bit.


LSL Tekpro

Graham Spriggs

Re: V-Type Return Idlers For Reversible Conveyors

Posted on 19. Apr. 2007 - 04:35

Morning Graham,

Thanks for the input.

The stiffening in the vertical plane is my point of concern. This is because if I set the return Vees too far apart, this might cause the belt to buckle and over time damage the carcass. Any guidelines here? Also, are there any equations that describe the conditions when buckling would occur?

Best regards


Re: V-Type Return Idlers For Reversible Conveyors

Posted on 19. Apr. 2007 - 08:18

Hello Barry..

There are formulas for return belt deflection that we use, but these are mainly of use when determining the resonant frequencies of return belt flap, and the harmonics thereof.

For normal calculations and as a rule, all you have to do is ensure that you never exceed a belt sag in excess of 2% of the return idler spacing.

The equation for this is:

T(min for 2% sag)=6.25 x 9.81 x belt mass/m x idler spacing in m /1000 kN

You will not normally need to concern yourself with anything more than this aspect.

Good luck

LSL Tekpro

Graham Spriggs

Re: V-Type Return Idlers For Reversible Conveyors

Posted on 19. Apr. 2007 - 09:33

Thanks Graham,

Will keep that in mind.

It's coincidental what you just mentioned in the beginning also had something to do with my presentation to a client next week to explain their spate of combined joint and pulley failures which I have put down to large start/stop transient loads caused by poor drive design.

Hope to get your inputs too in case I hit a wall.



Re: V-Type Return Idlers For Reversible Conveyors

Posted on 3. May. 2007 - 07:35

Dear Mr. Barry Chung,

Although there are varying and interesting replies, but as I can make out your question pertains to following two points and my response is accordingly.

1) V type return idlers improve the belt alignment. The longer belt conveyors are normally equipped with this type of idlers. The wide belt conveyors are also equipped with this type of idlers, as it is easy and worth to change the belt shape from flat to trough and to flat again.

2) You have asked about the implication on tractive pull / kW. Firstly, the two roll return idlers will have more rotating mass so this is to be accounted in calculations. This is adequate for engineering needs. The finer engineering aspect would also have the implication wherein the average pressure between belt and roller would be more due to inclined support to vertical gravity force. This will increase the belt denting flexure. The V shape idlers also introduce belt bending flexure. However, the implication due to these issues are quite small and therefore the same are ignored and it gets accounted in the contingency in calculation models. The return run total moving mass is quite less compared to the carrying run total moving mass. Again the aforesaid implications are applicable to lesser part of the resistances and therefore the aforesaid statement. Regarding the belt sag and its affect on V type shape, the design practice requires that the sag value should preferably be restricted to 1% of idler spacing. In this situation, V shape would not pose a problem.


Ishwar G Mulani.

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

Author of Book : Belt Feeder Design and Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916