Good day. I have an older, (1980 build) JLG 60FR series manlift with extending axles. It runs well on the Hercules gasoline engine but has a few problems I'm attempting to address. Not much available from JLG, or online with this machine so reaching out hoping someone with years back experience may help. I have all functions working both hydraulically, and electrically but wanting to optimize the machine for operation as looking to keep it maintained much better than has been in the past.

My main concerns are the Racine proportional valves and setting pressures in the machine. I have a small booklet given to me and it shows quick attach ports and has pressure readings too. Most of these ports are either capped, or plugged. However I'd like to know how the valve works, (or theory) so asking for an explanation if available.

Thanks kindly,