V-belts versus flat belt

[SLM]

Is there any advantage to v-belts versus flat belts?

I came across a photo of a dominion ES P/T with v-belts, but my own has a flat one. I’m due give it some tlc in coming months, and have been musing over “upgrading” to v-belts, which of course would also necessitate changing pulleys.

Any thoughts?

 

[Spectric]

It is all to do with power transmission, a V belt transmits power using the two angled sides and if it bottoms out then it loses this ability. A flat belt would need more tension unless it is toothed like an automotive cam belt and in these applications no slip can be tolerated. Then you have the polyvee which is flat and many grooves which also needs more tension than a V belt but can transmit more power in a smaller size depending on belt material and tension.

 

[SLM]

It is all to do with power transmission, a V belt transmits power using the two angled sides and if it bottoms out then it loses this ability. A flat belt would need more tension unless it is toothed like an automotive cam belt and in these applications no slip can be tolerated. Then you have the polyvee which is flat and many grooves which also needs more tension than a V belt but can transmit more power in a smaller size depending on belt material and tension.

Thanks Spectric, that makes sense. The existing belt is entirely flat, made from a very thing rubberised (?) fabric, and yes, runs at quite high tension.

 

[Fergie 307]

I converted my Kity planer to poly v, much less tension, and you don't have to worry about setting up the crowned wheels. I used a centreless pulley from a car power steering pump the same diameter as the motor pulley, then tuned down the original pulley to form a hub for it. On the cutter from I just turned a new pulley in alloy to suit the grooves on the motor pulley. Easy conversion of you have a metal working lathe.

 

[clogs]

flat belt types are ok for our machines BUT can the bearings take the strain.....
quite a lot of the cheaper machines use under sized bearing to SAVE money....
really doesn't matter up to 1.5 HP subject to bearings but I would prefer 3xV belts on the bigger machines......
Flat belt types are used in the auto industry because they will not fail on a tight radius.....
just to add if u have a 60'ish mm pulley with a V belt u really need a notched belt.....

I had very short belt life with my car lift, the pulley sizes were all out from the factory.....
so modded the system, a plywood pulley and to get more belt contact at the motor exra idlers.....used notched belts now.....
now modded for over 10 years.....
now has better bolting system on the wood pulley with a new cover....
it's a 2.5ton Hoffman.....

PS
Just changed the 4ribbed belt on my cars alternator....it's done 144,000klms.....
remember the bearings are designed for the tension.....

 

[ChaiLatte]

just to add if u have a 60'ish mm pulley with a V belt u really need a notched belt.....

...and to get more belt contact at the motor extra idlers.....

The statement about pulley size is meaningless unless you state the belt section you wish to use on it. A skinny vee-belt will run quite happily on a 60mm pulley. A fat section belt will have a much larger minimum pulley size.

The photo you show goes against all advice in vee-belt design guides - that they should not be subjected to reverse bending. That is one of the reasons polyvee is now popular as it accommodates the tortuous paths that modern car engines demand.

 

[Fergie 307]

Don't disagree with your comments about reverse bending, but his lift is going to be running pretty slowly, so rather less of a problem. But I too much prefer the poly v belts.

 

[Spectric]

The statement about pulley size is meaningless unless you state the belt section you wish to use on it.

An important aspect with a belt drive system is the angle of lap, this is the portion of a pulley that is either driven or drives the system. There was a car in the eighties, not sure which make or model but the crank pulley was so small that you could reach a point where the belt tension was now low enough that upon cranking the pulley just spun without moving the belt due to the sudden inertia of the crank and resistant offered by the camshaft.

Don't disagree with your comments about reverse bending,

Look at how some cars had really odd belt layouts, there was a Peugeot that had a belt that went through 90° s to drive a front mounted fan from the crank.

 

[Jacob]

Flat belts quieter, less vibration, more compact.
The completely flat un-ribbed are also much easier to fit. I had a Maxi 26 combi machine which had only one motor instead of the usual three. This was made possible by instead swapping flat belts over various pullies. Very quick and easy, no problem, good idea don't why it isn't used more often
PS they also twist easily and can link pulleys at 90º to each other, almost touching in a figure of 8 twist.

 

[clogs]

regarding reverse bending of belts.......
in the GOOD old days u were quite correct.....but those belts on my lift have carbon fibre strands.....not the old canvas carp......
secondly if u look at the angle relative to the main pulley size *now increased by 25%....too slow the lift down*
the belts are only in contact with the motor pulley a good deal less than 1/2 the poss grip /friction area...........
I tried the manufacturer to buy ribbed belts along with different size pulleys but they were/are not available AT ALL....
so thats my compromise.....those belts do actually last more than 2 years of regular use...
lifting the likes of Toyota Amazons and Isuzu Troopers....
without those mods I get less than 6months use from the set of 3....coz u could not keep the belts tight enough....
as the belts have now got a GREATER contact area I dont need to keep em so tight which helps the motor and shafting bearings......easy peasy......lol.......