I have a few heavy duty devices and a powered hub and I wonder what's the flow of current in those things.
No, they do not. A properly designed powered hub will fulfill the USB specification's requirement of providing 500mA maximum per port; if you connect a device whose current requirement exceeds that value, then the resulting behavior depends on the hub, but in general it simply will not source more than 500mA, and it certainly will not draw additional current from the hub's upstream connection.
USB hubs do exist which are capable of providing greater than 500mA on some or all ports, e.g. to support the iPad's 2A charging requirement, but they are invariably described as such; if the hub you're asking about isn't, then the only safe assumption is that it can't.