I am thinking of making a set up to drop a heavy weight (old forklift
counterweight) onto objects, such as truck cabs and file cabinets, to
flatten them in preparation for scrapping. That way they will take
less room in the scrap gondola.

To drop that counterweight, it would need to be lifted with a
forklift, and then some sort of a release-under-tension would release
the object and it would fall.

I have compressed air nearby if I wanted to make that mechanism
pneumatic.

Any suggestion for something that could release an appx. 2-3 ton
weight?

i