It is simple really, more moving parts i.e. pins, bushings, rollers, sprockets and idlers, will always be more cost per ton/unit than less parts, which there are many less parts in a VGF and 90% of those don't even touch material!. However apron feeders have there place and there is no reason to replace something that works fine and doesn't brake, this does not seem to be your case, so when replacement comes you will have to weigh your options. The math is this. Lets say your complete jaw plant costs you $1 ton to operate and 10 cents of that is your apron feeder, lets say you can operate a VGF for 5 cents and you crush 100,000 tons in a year that is $5,000 less cost per year! i think these numbers could be close to actual costs. Would this make the payments on a new VGF with just the savings?........TIO