Kubota 3rd Function Valve: Continuous Use OK?

[JWR]

LD1 said: IF you start the tractor up, and raise the 3PH lever, then immediately (before the 3PH implement is raised all the way) you grab and raise the loader, the 3PH will "pause" its lift while raising the FEL. Once you are done raising the FEL and let off the stick, the 3PH will resume its raise.

Yep. That is exactly what I said. It is one track mind hydraulics. You are moving under hydraulic power only one thing at a time. I did not realize the MX lacked a separate pump for the 3PH. My MF2660 has a separate 3rd pump for the 3PH.

LD1 also said "It goes Pump > Loader Valve > Remotes > 3PH." They are all open center and when you move a lever to open flow for any one of them then the others wait. In your example your raising the loader forced the 3PH to wait. I am puzzled how the pecking order (priority) is established however.

 

[LD1]

The pecking order is establish simply by a function of how its installed.

The 3PH is almost always the last in line. Why....because it doesnt have an external valve with a power beyond to feed anything else. And almost always had the "return or tank" just plumbed internally. No external lines.

So that really only leaves loader and remotes than can be swiched. The pumps are normally up front by the engine. So it just makes sense to feed the FEL first, then the remotes, then 3PH.

versus going from the pump at the front of the tractor, to the remotes at the back, back up to the loader, then back to the 3PH again. One could certainly do it and make the remotes take priority over the loader, but in the real world.....what benefit will that gain you?

 

[JWR]

The pecking order is establish simply by a function of how its installed.

The 3PH is almost always the last in line. Why....because it doesnt have an external valve with a power beyond to feed anything else. And almost always had the "return or tank" just plumbed internally. No external lines....

So the pecking order is established by which control valve is fed first and then second, etc. outward from the pump. In practice that means if something is further out in the chain from the pump, it waits whenever anything closer to the pump gets actuated, right ? And anything further out will just not work until you let up on the closer-to-the-pump control. Does the power beyond port supply the next guy out the chain (in the case of the MX5100 the power beyond port on the loader valve feeds the remotes?)

I assume that means the first valve encountered from the pump outward (in MX5100 case, the loader valve body) has to have the relief valve in it to set the system pressure.

 

[LD1]

IF pressure relief valve is in a valve, yes it is typically the first one.

You kinda sound surprised at all of this. Its the way it has always been. How many functions do you need to operate at the same time?

Now a closed center system is a whole different animal.

 

[JWR]

What about when you're digging into a pile of dirt? I can move forward with my HST transmission on my Kubota BX25, while at the same time curling the FEL Bucket upward to fill it with dirt.

Your HST transmission is not the same hydraulic pump that runs your FEL, remotes if you have them, etc. The HST is one huge hydraulic pump in and of itself, driven directly by your engine and not supplying high pressure hydraulic fluid to accessory devices. Curling your bucket to pickup material is independent of driving the machine under HST power.

 

[Xfaxman]

Depending on the flow rating of the pump and the engine RPM, if you raise the loader slowly, you can curl the bucket at the same time.

 

[JWR]

IF pressure relief valve is in a valve, yes it is typically the first one.

You kinda sound surprised at all of this. Its the way it has always been. How many functions do you need to operate at the same time?

Now a closed center system is a whole different animal.

Yes, I do not have a closed center system. And it may have always been that way but there are many who do not understand everything about what they are operating, like me. Also a wide variety of configurations of course. Somewhat off of the original post, but a couple of years back I was running a 5ft rotary brush cutter (more typically used with a skid steer) mounted on the FEL of a MF2660 tractor. A dealer had sold me the entire rig, plumbed it for me, and saying that, on paper, I had adequate hydraulic flow, etc. The hyd motor for the cutter was run off the 3rd ftn lines going up to the loader (which I normally use for a pinch bucket.) It came as a surprise to him and nasty shock to me that any lifting of the FEL or curling or dumping (other than gravity assisted moments) shut off the hydraulic motor driving the cutter momentarily and then turned it back on with a bad jerk after you stop moving the loader. That created a lot of unwanted stops and starts of the rotary cutter, needless wear and tear, etc. I might have gone to serious lengths with flow control valves, etc. except for the fact that the tractor really did not provide the flow needed to run the cutter without nuisance clogging when cutting brush. Other things I use like a hydraulic top link are so intermittent / rarely actuated that they did not matter.
End result was I traded the cutter off on a rear mounted boom cutter with 2 of it's own pumps and totally independent of tractor hydraulic pumps.

 

[MHarryE]

Engineering wise the critical component is the hydraulic pump. All Kubota tractors, except for the M7, use gear pumps. Not sure which brand pump Kubota uses but in general, gear pumps are good up to 85° C continuous (185°F) or 90°C (194°) intermittent. If you are going to use the PHD for long lengths of time I suggest investing in a laser temperature gun (can be surprisingly inexpensive and accurate enough for what we are talking about) and check items like your pump, filter (suction filter just prior to the pump on all my Kubotas). My largest Kubota has detents on 3 of its 4 SCVs and one is prone not to automatically kick out of detent when the cylinder hits the end of the stroke. When I have noticed this after a short time (the pump running over relief uses a lot of power so it is noticeable in tractor operation) I have checked pump and filter temp and found them well over 200°F - it does not take long to heat the oil at high pressures even with an oil cooler in the loop.

 

[dfkrug]

Most modern loader valves are plumbed funky internally. In series & parallel or something.
So you can lift & curl at the same time. However that only exists in the loader valve body & doesn't permit the same
functionality on the power beyond loop.

There's a technical name for that: it's called "tandem-center". Essentially the multiple spools in your monoblock or
stack valve have connected IN lines in parallel. If you pull both levers on your FEL valve, say
boom-down and bkt-curl, hyd oil will go to the spool with lowest back-pressure. That is how you use 2 valves at
once. You can vary the back-pressure in one spool to balance the flow to the other by restricting the flow
to one by "feathering" the lever.

As stated, this does NOT work this way to other valves in the PB path.