i will try to explain why a generic valve versus correct pieces will function differently.
the original JD valve will have specific machining on the spools to achieve the desired effect on the function. For example would be boom down (hoist) will likely have the spool machined to provide back pressure when lowering to keep the boom from falling too quickly. You may also have internal porting to allow for series or parallel flow to allow certain functions to be run simultaneously
A generic valve is going to have none of those features. It will simply be machined to function.
Interesting concept about the machining of the spool - and of course it carries over to machining of the ports as well as maybe even some machined in controlled regeneration.
The thing is, I don't know if any of it actually is real. I just don't know about the valve industry. I do know that different control valve bodies have a different feel, that they do wear out, and that finding a valve with low flow controllability seems to be more rare than finding one with high flow speed. I assume the difference may be is in the small machining and engineering details -that would explain the price difference between cheap and expensive valves.... but again, I don't actually know that. It could also be greed.
One possibility would be to see is we can find a backhoe valve manufacturer willing to educate us on the subject.
Another idea would be to sit down and think as the OP did when he originaly questioned the need for a valve with a 23 gpm flow rating and wondered if a 12 gpm vavle work? Lets think on that for a minute.
Our JD310 BH flows 36 gpm and the Kubota M59 BH flows something like 10/15 gpm to the hoe. We use both at about the same boom speed with motor on high idle and on neither one do we use "full open" on the control valves...or at least not often. So we rarely ever get to 12 gpm (except lowering the outriggers). And even if we did, in today's typical OPEN CENTER hydraulic syste, an inexpensive adjustable diverter valve would answer. Simply feed the BH valve with 12 gmp and send the rest back home to the sump.
However. the OP says his old JD BH has a CLOSED CENTER hydraulic system. I love those old JDs - built to be rebuilt forever - and If I understand that type of system correctly it might not even need the diverter. In a closed center hydraulic system, the variable stroke pressure pump only creates as much flow/pressure as is needed & when the pressure tank is full the pump rests. That's the main advantage one gets for all the complexity of a closed system.
So in that system - if I've got this right - the backhoe control valve itself would not accept a higher flow than 12 gpm and the closed center pump would relax into low stroke mode. This is a fairly low pressure closed center hydraulic system by today's standards and that helps too.
If going that route, I might decide to put in an adjustable diverter valve anyway. Couldn't hurt; might help. If so, then in that application I
think there would be no difference between an open and closed system as far as which diverter valve to use.
rScotty
