GC1700 series fast dump loader function??

[aczlan]

You lose me in the higher and lower pressure discussion. So far as I know there is only one high pressure level from the pump, controlled at that level by a relief valve, and fed to where ever the control valve directs it.

Let's start here, since the difference is what makes regen dump work.
Here is a generic hydraulic cylinder:

If the bore (the diameter of the inside of the cylinder housing) is 2" and the diameter of the rod is 1", there is enough surface area that if you put fluid into the blind or base end at 2000PSI (with no pressure on the rod end) it will try to extend with 6283# of force.
If you put the same 2000PSI into the rod end, the surface area of the disc on the end of the rod is smaller due to the diameter of the rod, so it will only retract with 4712# of force.
If you put 2000PSI into both sides with them tied together (like regen dump does), it will extend with 1571# of force due to the difference in surface area on the disc that is mounted on the end of the rod for the hydraulic fluid to push on.

Does that make sense? Do you follow me so far?

Aaron Z

 

[Snobdds]

All I know is, when I put the joystick all the way to the right, the bucket will dumb noticeably faster...

Which is all I want...

 

[aczlan]

KennyD explained it well:

Regen is a "feature" of most modern FEL (Front End Loader) valves, it's on the Dump (joystick far right) circuit, and is also referred to as "Fast Dump". The reason it is nice to have is that without it, the weight of a filled bucket can actually "pull" the bucket down faster than the fluid can enter the other side of the cylinder, this will create a air pocket and give the bucket a "floppy" feeling until the joystick is held in the dump mode a few seconds to refill the cylinder pushing the air past the seals. So we add "regen" or "regenerative" function to the valve.

Regen solves this problem by actually filling both sides of the cylinder at the same time with hydraulic fluid. But how will that work you might ask? Well, because there is more volume on the side of the cylinder that extends it since the rod is taking up space in the other side, it "overpowers" the rod side and lets the cylinder extend-thereby dumping the bucket. So since now both sides of the cylinder are "pressurized", the air pocket can not develop, eliminating the "floppy" bucket syndrome. One other added bonus is that the bucket actually dumps faster due to the higher flow rate required to do all this, that's why it's referred to as "fast dump" sometimes.

Aaron Z

 

[JWR]

Aaron: Outstanding posts #31 and #33. I really appreciate your patience here !! Causes me to re-think several issues, cases where I thought something was wrong, etc. I find it interesting that my loader manual and your explanations do not contradict one another -- it's just that the operators manual [post #30]
did not go far enough to explain the situation. I am stunned. Never too old to learn. In post #31 you asked "Does that make sense? Do you follow me so far?" and the answer is YES, for sure.

Obviously I was wrong in several posts above, based on thinking that fast dump was strictly gravity replacing hydraulics.

I am assuming that "regenerative fast dump" is standardized terminology such that your explanation applies to all brands and sizes of loaders if they have the feature. Given the added complexity and cost of the loader valve, I am still surprised that the feature is found on smaller tractors like the GC1700 series.

 

[aczlan]

Aaron: Outstanding posts #31 and #33. I really appreciate your patience here !! Causes me to re-think several issues, cases where I thought something was wrong, etc. I find it interesting that my loader manual and your explanations do not contradict one another -- it's just that the operators manual [post #30]
did not go far enough to explain the situation. I am stunned. Never too old to learn. In post #31 you asked "Does that make sense? Do you follow me so far?" and the answer is YES, for sure.

Obviously I was wrong in several posts above, based on thinking that fast dump was strictly gravity replacing hydraulics.

I am assuming that "regenerative fast dump" is standardized terminology such that your explanation applies to all brands and sizes of loaders if they have the feature. Given the added complexity and cost of the loader valve, I am still surprised that the feature is found on smaller tractors like the GC1700 series.

Thank you, glad I was able to make sense.
As for added complexity, as I understand it, all that they need to do is add another half inch or inch to the loader spool and grind a different set of openings into it. Then they put a different spring on the outside and its good to go.

Aaron Z

 

[JWR]

...
As for added complexity, as I understand it, all that they need to do is add another half inch or inch to the loader spool and grind a different set of openings into it. Then they put a different spring on the outside and its good to go.

Aaron Z

That's the way it seemed to me when I had my loader valve apart, I just did not understand what I was looking at. There is another (lengthy textbook style) treatment 'of regen fast dump' at BOOK 2, CHAPTER 17: Regeneration circuits | Hydraulics & Pneumatics. The Hoyetractor article is by far the most readily available insight on the web into the feature.

The longer the spool gets, the greater the chances of the "plus and minus" tolerances adding up in one direction along the length of the spool. That is what NIMCO said had happened with their valves. In other words, each dimension was within tolerances originally set, but if all or most were off to either plus or to minus side, then the one out at the end was in trouble. The kit they sent me was to fix that out at the far end.

 

[atsah]

Sorry, but the physics of the circumstance does not support your observation. The fact that it "picks up the front of the tractor doing so" proves that the bucket dumping motion is hydraulic driven. There is nothing about a quick dump feature that provides more hydraulic pressure nor more sudden volume of hydraulic fluid flow nor anything else (other than gravity) to produce the motion. Just does not happen. In fact, the bucket being driven downward under hydraulic pressure proves you were NOT in the quick dump mode at that point (!) You were in the normal dump position of the loader valve.

This was you're reply to my post. To me this post says, atsah, you have no idea what your talking about because what you explain is not possible.

That's why I kind of got upset, make sense?

 

[JWR]

This was you're reply to my post. To me this post says, atsah, you have no idea what your talking about because what you explain is not possible.

That's why I kind of got upset, make sense?

Well, I am sorry. It was not meant that way at all. I was trying to be strictly factual, not nasty. At that point, it looked to me like your observations and what I believed to be facts were directly contradictory. Maybe there is a better choice of words to say "I think you are wrong." Turns out I was wrong anyhow (aside from my tact or lack of it.)

 

[atsah]

Well, I am sorry. It was not meant that way at all. I was trying to be strictly factual, not nasty. At that point, it looked to me like your observations and what I believed to be facts were directly contradictory. Maybe there is a better choice of words to say "I think you are wrong." Turns out I was wrong anyhow (aside from my tact or lack of it.)

It’s no problem at all.. Technically I really didn’t know myself why the loader worked the way it does, I learned something myself.

 

[lpakiz]

OK, I hesitate to jump into the middle of this, but i believe that “fast dump” and regenerative circuit” are one and the same.
As I understand it, these valves are very valuable on a woodsplitter, where the “retract” doesnt need to develop much pressure, but VOLUME is most important. The more VOLUME of oil entering a cylinder port, the faster that cylinder travels.
So, as I understand it, in RETRACT) the “regen” valve combines the normal oil flow from the pump to the retract port but simultaneously intercepts the “return” oil from the “push” side of the wood splitter (which would normally be returned to the resevoir) and directs it into the retract port. So now “retract” has its normal volume of oil, PLUS the intercepted (diverted) oil from the push side (which would normally be returned to the resevoir) and uses the combined flow to move the piston really fast, but pretty weak. Perfect for a wood splitter or loader bucket curl function, where you want speed but dont need the power (force).
Not very useful on most hydraulic circuits, but works great on these functions.
And I tend to agree that these valves could be more trouble than they’re worth, especially if they are not designed correctly. Then again, engeneered correctly, there might be some extra value in them.
I disagree that the dump cylinder can “suck air from the resevoir”, because said air would also need to be sucked thru the pump and valve in order to get into the cylinder.