We are considering possibly making a purchase of a hyd forestry head cutter to be mounted on our 318BL Cat excavator & as there are flow requirements for each size of cutter I wanted to ask if anyone would have a way to look up what this machine may produce flow wise? Ser # is 3LR00468. We do have a hyd thumb on the machine & for operating the forestry head we would use that supply to power the attachment, or at least that is the plan if it is doable. Looking at the specs from one manufacturer a 36" head size takes 24-32 GPM & a 48" takes 40-80 GPM.
As far as I can tell, that machine was shipped without any auxiliary hydraulics fitted, so whatever is controlling your thumb must be an aftermarket fitment. That means it is probably working with one-pump flow. It is possible to make it two-pump flow, but it's complicated. The bench test spec for one pump is around 35Gpm but when you account for the losses in the lines, you won't see that figure at the end of the stick. The best thing to do would be to get someone to put a flow-meter on the auxiliary lines and see what you really have.
The auxiliary function spool is already in the main control valve and has only one pump flow. The machines did not come plumbed from the valve to the end of the boom or stick. The key spec you need to know is the flow at a specified pressure. The pumps are variable flow so might put out 35 GPM at 1,800 PSI but would likely be half that at 2,500 PSI. So you need to know the pressure rating on the attachment along with the minimum flow requirement. The common way to run an auxiliary hydraulic motor for a mulcher and still be able to run any other functions is to obtain two pump flow. I believe there is a provision in that model of machine through a blocked off port on that main valve to join up two pump flow. I know it is done on logging shovels that were running processors. Someone on here might chime in with some education on that point.