Serpentine Belt Tensioner

[krue0101]

Hello,
I am applying a 6 rib serpentine belt on the front of an engine and have been told by the belt supplier to apply 120 lbs of tension in the belt. The also suggested that I install an automatic tensioning device.

I don't know how to calculate the tension in the belt in relation to the force in the tensioner. Can anyone help?

It seems easy, but I am confusing myself as I have never done this before.

Any help would be appreciated.
Thanks

 

[haggis]

krue0101

Does the belt require a total tension of 120lbs or does the tensioner have to provide 120lbs giving a tension of 60lbs on each side of the belt as it goes around the tensioner?
If the tension on each side has to be 120lbs, then the tensioner would have to provide 240lbs of force.

Regardless, you would have to know the rating of say a spring loaded tensioner to buy the right one.

Unless I am completely misunderstanding the question, every force has an equal and opposite reaction so whatever force the tensioner the tensioner exerts, the entry and exit sides of the belt would be sharing that pull.

Haggis

 

[Tmoose]

The resulting belt tension depends on the angle the belt runs form with each other at the tension point. A few pounds of >>force<< from a tensioner causes hundreds of pounds of >>belt tension<< if the belt stays at a low angle.

 

[sacem1]

When a belt manufacturer specifies tension it is the pull you must exert on the tensioning screws that usually are fitted on on end of the belt acting on the floating pulley shaft, true a reaction will occur at the fixed end but thats not something you have to create it will just happen so you have to produce the 120 lbs on the regulating point.

The angle is 0º because all belts will self align with the tensioning pulley so the tension will be 120 lbs net.

Usually this is a referential tension and your device will work even if you are 20 to 30 % out of the mark so don't worry too much on it, if you really want to now how to get the 120 lbs you can buy a chip dinamometer ( a spring scale by other name) put a piece of rope around the floating shaft and pull with some help from another person or using a chain winch or similar device until you have the 120 lbs reading on the scale, mark the position of the pulley shaft and afetr releasing the rope retighten the screws until you reach the said mark, you should be very near the requiered tension
This is easier than calculating the tension with the screw lead, because you will have to assume a lot of variables like friction between nut and screw, etc.

Cheers.

SACEM1