Hydraulics Help Needed

   / Hydraulics Help Needed #11  
Regular spool valves are proportional... more or less. How proportional depends on the quality of the valve, how well it's matched to the system, and what it's driving. I got to run a good size Kubota excavator for a little bit yesterday and the electric over hydraulic proportional control valves are miles better than anything I've used on a tractor or tractor backhoe. And it does the multiple valves at once thing much better too. But it's also a lot more expensive.

Spool valves should be sized for about 25% more flow than the system they're on.

Valves down stream of the loader valve on it's power beyond do not have to have power beyond ports themselves.

Loader valves should have a power beyond to run the 3pt hitch or other valves. You can get loader valves with two sticks or a joystick. I'd recommend a joystick, and a valve with a float position for the loader. Well matched and well made loader valves should let you raise/lower the loader and curl the bucket at the same time.
 
   / Hydraulics Help Needed #12  
...Valves down stream of the loader valve on it's power beyond do not have to have power beyond ports themselves....

Then how does pressure get back to the 3PH if the former (loader valve) PB port now supplies the valve downstream instead of the 3PH...??
 
   / Hydraulics Help Needed #13  
The loader's PB connects to the new valve's in port. The new valve's out port goes to the 3pt's in port rather than to the tank.
 
   / Hydraulics Help Needed #14  
The loader's PB connects to the new valve's in port. The new valve's out port goes to the 3pt's in port rather than to the tank.

Then why does the loader valve need both a return/tank and a PB port ? why doesn't the loader valve's tank line power the 3 PH ?
 
   / Hydraulics Help Needed #15  
Because with the PB and tank separate, there's always a guaranteed low pressure route to the tank. When you move the loader there's oil coming out of the cylinders and it needs a place to go. Without PB, if you operate a downstream valve at the same time as you move the loader, the loader would stop because it would see high pressure on both sides of the cylinders.

Assuming that your downstream valves and lines flow without much restriction, there should be no difference between PB and non PB loader valves when you're not operating a downstream valve.

I think some loader valves also can route some flow out PB when the loader is being used at less than full flow. Mine doesn't appear to (and that's what the manual says too).
 
   / Hydraulics Help Needed #16  
My gravel driveway where I used to live would get washboard real bad because it was on a hill. I made a blade that mounts under the tractor just in front of the rear wheels, with arms that bolt to the 3ph arms, to raise and lower it. It worked great, and made the road nice and smooth. It's just a matter of the physics, where the front wheels going over a bump don't move the blade much. It's why road graders are made the way they are.
 
   / Hydraulics Help Needed #17  
The loader's PB connects to the new valve's in port. The new valve's out port goes to the 3pt's in port rather than to the tank.

That is not a proper installation. When the 3pt load increases system pressure to near relief pressure the tank side of your non PB capable valve is subjected to this pressure and the spool seals usually fail. In a big way. The 3 point hitch valve IS a downstream valve.

Your posts 11 and 13 contradict each other.
 
   / Hydraulics Help Needed #18  
Pardon the interruption. But can each of you describe what you mean in detail? I am in the process of installing a new spool valve on a L3700 Kubota and I am now confused!
 
   / Hydraulics Help Needed #19  
Here's a diagram that came with the hydraulic spools when I added to my tractor. It's the best diagram I've seen that shows what needs to be done.
 

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   / Hydraulics Help Needed #20  
That diagram is good but don't forget the 3pt valve in the transmission is the last in the chain. The added valve can't have it's output tee'd into the tank line or the 3pt won't work.
 

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