did search from what i can tell the whole purpose of the dual alt pully is to reduce the amount of force needed for the pulley by using 2 belts?

But do u put the same belt and just put both of them on the pully for the alt and water pump. guess im just a lil confused by what it means?

 

When people remove the air pump and its belt, it removes one of the drive belts for the water pump. The dual alternator pulley allows you to run 2 alternator belts to prevent belt slippage.

 

and since 2 belts of the same size are used,the alternator now becomes the adjuster,so to speak.
you tighten the belts by raising the alternator up and tightening the nut on the alternator bracket.
the Purpose of the 2 belts is not for the alternator,but to prevent the water pump from slipping.If you take off the air pump off, the water pump only has one belt to rely on.With the extra belt and dual pulley on the alternator, the water pump now has twice the amount of belt contact so it will be less prone to slippage.