why does using FEL stop Power Beyond flow

[ovrszd]

I'm not double jointed enough to run my joystick and 3pt lever or rear remote levers at the same time. I suck....

 

[orangetree]

My question is why? What real world issues are you having/seeing that have you questioning the function of the PB?

Your hand drawn sketch.....trying to use retruning oil from a cylinder as its moving to feed the PB is not as cut and dry as it sounds.

First question.....WHAT are you trying to do with the PB while you are also raising the moving the loader?

The 3PH is something typically fed off a 3PH. So lets say you are trying to raise the 3PH while ALSO trying to lower the loader. BUT, you dont want to feather the FEL valve....so you want oil returning out of the base of the cylinder to go on to feed the 3PH and make it raise whatever, is that right?

If so, lets do some math shall we......

Lets say you have a 2" cylinder with a 1" rod for the loader. As you are lowering the loader. @ 2500psi.....your retract power per cylinder is just shy of 2000# plus a little help from gravity. That 2000# plus gravity is EASY to push that oil right back to tank through unrestricted passages.

But....now the path is restricted....because now you want to direct that flow to the lift cylinder for the 3PH.

Well, that 2000# of force acting on the 2" piston is only enough to muster ~630psi of pressure....add a little more for gravity helping it).

IF you are trying to lift something on the 3PH that requires more than that.....no dice. You try and lower the loader and raise the 3PH at the same time and NEITHER will move. Hence the whole purpose of power beyond.

If you really want to separate the incoming flow in the loader valve with the PB.....remove the PB from the equation. Convert the loader back to a simple open center valve. Install a flow divider before the loader valve and dedicate whatever you want to the loader, and the rest to the PB

the example with gravity is a good one, except for the fact that the "bad" condition there is user-choice. If speed of movement on that one cylinder is the user's priority, then they would not operate a downstream function (because, as you say, the "backpressure" would interfere with their priority operation.

forcing it to tank makes this choice for the user, in all cases. No option to use the full tractor flow while feathering, because some is being diverted. Perhaps this is just cheaper to make a valve this way? I don't know enough about internal routing; obviously many valves can support both high-pressure "tank" cavity and bridge/divert that to PB (sometimes optionally with 'sleeve')

One example of what I'd want to accomplish, is full-speed movement of the grapple while also moving the FEL arms or curl.

Of course I'm limited by the total pressure available to me, and if more than one cylinder encounters resistance (builds pressure) that will be divided among the cylinders.

 

[LD1]

Even with your grapple scenerios, tying return cylinder flows to another function you will encounter backpressure issues that need overcome.

Like trying to raise the loader and close the grapple to squeeze tight. You are effectively using the exxtending hydraulic cylinder as sort of a mechanical pump to fill and close the grapple cylinder. Which will reduce the lift capacity of the loader...because you are now fighting the backpressure on the rod side. And you could also over-pressure the grapple circuit. Because with a 2" cylinder and 1" rod on the loader.....you are lifting with 2500psi pushing on the 3.14sq inches on the base of the piston. But block the rod port (exit fluid feeding cylinder), that side of the piston only has 2.36sq inches of area. Meaning you "could" generate close to 3400PSI in the grapple circuit.

It almost sounds as if you would be better served with a closed center system and variable displacement pump rather than try and re-invent an open center system.

 

[orangetree]

It almost sounds as if you would be better served with a closed center system and variable displacement pump rather than try and re-invent an open center system.

I do appreciate the replies, but no offense, but this is a pretty standard non-answer.

Closed center is superior to open center in just about every way except cost. Which is why us small-tractor owners are stuck with it; manufacturers have more incentive to hit a price point, and even for informed buyers (many are not...) unless they're really looking for simultaneous operation, specifically, the cost might not even be worth it. And thus economies of scale dictate it's not even offered. So, of course I would be better with closed center; and had it been an option I would have upgraded to it ...

I'd reckon > 2/3 of my "movement time" for the FEL/grapple circuits is not pressure/power limited. Dropping, positioning, etc. All of these actions would be spead up considerably if both actions work simultaneously at full speed (-vs- the stock split-flow/partial speed)

Most (all?) valves which support "full pressure tank" cavity can support a flow pattern (all flow to PB, not tank) that supports this improvement. So I'm trying to spec a system to do this. Title of this thread is phrased to look for any reasons I wasn't aware of the systems are not done this way.

The only reason identified so far is that *iff* one doesn't understand that you're still pressure-limited with this "series" configuration, they might be surprised by reduced power on "X" if "Y" is activiated ... ie, the least common denominator of a user. Common, but unfortunate.

 

[oldnslo]

Orange
A point you might be missing with series circuit is in trying to run multiple functions is that when a function bottoms out ALL functions stop.

example grapple full open and bucket close to level. If you curl bucket and close grapple, grapple will stop as soon as bucket is curled back fully.

 

[orangetree]

Orange
A point you might be missing with series circuit is in trying to run multiple functions is that when a function bottoms out ALL functions stop.

example grapple full open and bucket close to level. If you curl bucket and close grapple, grapple will stop as soon as bucket is curled back fully.

Correct, totally get that.

the moments where a cylinder is bottoming out and the OP valve would activate are a tiny fraction of the entire cycle of operating the system; so this is more functional for my use just considering the grapple use.

However, it gets even more important if I am able to get to my controls project to auto-level the TnT; now of course FEL/grapple usage isn't that critical (not loading when dragging a 3pt implement), but full speed control to both (or all three if i go that way) cylinders simultaneously in the TnT is critical to have response times. Even more so than with the FEL/grapple, these cylinders will ~never bottom out, nor do they ~ever require the full hydraulic pressure (3point is entirely implement-weight driven; after all the hitch rises freely)

 

[WranglerX]

Could also be that when operating loader when control valves are operated and the flow from valves are diverted from PB but to tank.... Pressure to PB may only be percent when FEL valves are all in neutral position.... If you have brand name of control valve and you can find a schematic of flow through valve maybe you question would be answered...

This is schematic for my FEL control valve for my MF GC 1715.... If you can find similar schematic for you tractor it may answer your question...