Lots of knowledge here. Time to go back to the well:
For info, I decided it would cost just as much to change all the fittings as to simply bite the bullet and purchase the "Kubota" fittings. So, I now have to remove the fittings from a new grapple and install the "Kubota" fittings.
I have my control lever set so that the top button opens the bucket (I have a 4-1 bucket) and bottom closes it. I'd like the grapple to work the same way.
My tractor connections are arranged so that the male fitting is positive pressure, female releases pressure. When I put the fittings on the new grapple, is there a way to tell which fitting to put on which hose so that the buttons will work the same way?
Of course I could just install and have a 50/50 chance of getting it right the first time but thought I'd ask here.
Thanks.
Lets address the bolded text a bit. It would be best to think of hydraulic fluid routing by your control valve as changing the routing of the fluid flow not pressure. Pressure does not build until the fluid flow encounters a restriction.
In an open center hydraulic system the fluid comes from the tank, and into the inlet or suction side of the pump. The pump does not make "pressure" per se, it just makes fluid flow. Now the outlet of the pump is making fluid flow all the time at so many gallons per minute.
In my tractor that rate is about 10 gallons per minute. So now the fluid is flowing toward the FEL control valve inlet and right back out its Power Beyond port heading towards my rear remote valve and right back out heading towards the 3 point control valve and then dumps back into the tank.
Not much pressure is developed during this entire trip around the tractor.
Why is that you ask? Well hopefully the restriction of the fluid flow, now flowing through all of those valves in neutral is pretty low. Sure some pressure will rise due to the restrictions in the valves and hoses and all of the fittings, but no where near the 2500 or more pounds of pressure the relief valves are set for.
Now lets say that you pull back on your FEL valve to lift the main FEL boom. Now you have routed the fluid flow to a set of QD (Quick disconnects) attached to your FEL valve. One of these QD's have the fluid flow coming out of it, and will be plumbed to the cap side of your lift cylinders. (they are plumbed with a T connection so that both cap ends of the lift cylinders receive the fluid.
The other QD is connected to the rod sides of your lift cylinders and as the rods extend the fluid in the rod side of the cylinders flows out of the cylinders and back to this QD. In your FEL Valve, it also routed that rod side QD, back to a hose that flows fluid back to the tank (your tractors transmission is your tank) All of that happened by you pulling back on the joystick control.
The pressure spiked up a great deal as the weight of the loader arms and bucket offered a resistance to the flow of the fluid in the cap side of the cylinder. If you had something heavy in the bucket, the pressure spiked up a great deal more as it offered even more resistance to moving up.
So you see the pressure only rises when the fluid flow has something to push against. The harder it is to push the fluid down the "pipe" then the higher the pressure rises until somewhere in the system a relief valve say "enough" and opens the pressure path back to the tank to prevent something from turning into a grenade.. Hose, valve housing, pump, breaking shafts on the engine.. Something has to give. Hopefully just the relief valve.
Now when you move the FEL control back to the center position, the fluid flow is just routed back to the Power Beyond connection and the fluid flow goes downstream and winds back up in the tank after going through all those other valves. Of course the fluid trapped in your cap side and rod sides of the cylinder has no place to go so the lift just stays up.
Now lets push the joystick forward. OK the other (rod side) QD now has fluid flow heading towards the rod side of your lift cylinders and the rods start to retract as the fluid pushes piston back towards the cap end of the cylinder and the cap side of the cylinder is opened to tank by the FEL control valve routing. Now you lift arms start to fall.
OK the curl and dump cylinders and valve position and QD's work similarly. This is a simple explanation, and we can get into regeneration in a later rant.
So now you know that when you say one of my QD's is positive pressure, and the other releases pressure, that is not quite right. Both are flow from the pump and both are flow back to the tank, it just depends on which of the buttons you press. Pressing one button makes the fluid flow from your 3rd function electric/hydraulic valve to one of the "work ports" and its associated QD. This causes you 4n1 buckets cylinders to extend by applying fluid flow to the cap side of those cylinders. The rod side of those cylinders are opened to the tank. When you press the other button the electric/hydraulic valve applies the fluid flow to the rod side of the cylinders and the cylinders retract.
I hope this helps a bit.
