3 position valve-vs-4 position valve

   #1  

kubmech

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<font color=purple>I see this question come up alot, so I thought I'd make it a little more "searchable"</font color=purple>

The 3 position valve and the 4 position valve, both have what is known as a regenerative circuit built into the bucket dump circuit.

First let me explain what "regen" is and why.

When dumping a loaded bucket (with a good old fashioned loader control valve) the weight of the material in the bucket tends to pull the cylinders down faster than the hyd. fluid can fill the other side of the bucket cylinders. Therefore, an air pocket will develop in the cylinder causing the bucket to be a little "floppy" unless held against relief for a few seconds at the end of the dump cycle. Which creates an extra step if you want to back-drag, etc.

To solve this problem we now add a regenerative (regen) circuit into the dump function of the loader control valve.

What is "regen"? The dump function of the loader control valve applies hyd. "power" to both sides of the bucket cylinders at the same time. But Kubmech, how the heck is that going to work? Wont the cylinder just lock up and not move? No, because on one side of the cylinder the rod itself takes up space, decreasing the volume of the cylinder, on the other side of the cylinder piston there is, no rod, creating more volume. PSI=pounds per square inch, the more volume the more square inches to apply pounds, get it? O.K. so the back side of the cylinder overcomes the front side of the cyl. due to more volume and at the same time does not allow an air pocket to develop becuase of the added resistence of "hyd. power" to the front side of the cyl. allowing the cylinder to "stay tight" for subsequent operations. And as an added bonus it tends to dump faster due to the higher amount of flow/pressure to perform this operation. (Hence the "fast dump" mode the salesmen love to tell you about) In actuality the "fast dump"
mode is just derivative of the regen circuit.

Soooo..... What's the difference between 3-pos. and 4-pos. valves, besides about 35 bucks.

The 3-pos. valve has regen in the dump mode period. The problem with regen is if you want to add, say a snow plow, with power angle running off of the loader control valve, the power angle works off of single acting cylinders. With "hyd. power" being supplied to both sides of the cylinder, you will only be able to angle in one direction and that's it. (back to the whole volume-vs-psi thing again).

The 4-pos. valve has a detented position. When moving the control lever to the right, to dump (or power angle right in the case of the plow) if you choose the first detented position this is the non-regen position and will work just like the good old fashion loader control valve. If you apply a little more pressure on the control lever you will push past the detented position and move into the regen position. Thus, if you have the 4-pos. valve and want to avoid the floppy bucket syndrome you have to push full right to engage regen.

So the bottom line is; both the newer 3-pos. and 4-pos valves have the "fast dump" option. The difference is, do you want to add options to your front loader without having to add an aux valve to you're tractor or not?
 
   #2  

MarkV

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Kubmech,

Very nicely explained. Even I - hydraulically challenged – now have a much better understanding of regenerative circuits. Are there other examples of attachments that normally use a regenerative circuit?

Sure is nice to have a few of the pro’s around to get us straightened out./w3tcompact/icons/smile.gif

MarkV
 
   #3  

Harv

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Hey, thanks, Kubmech!
smile.gif


My understanding of tractor hydraulics is superficial at best, but you've cleared up at least some of the mystery here. I've saved the text of your message in my "tractor notes" folder on my computer.
wink.gif
 
   #4  

Bird

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Aah, thanks, Kubmech. I knew that I had the 3 position valve, and I knew that it would dump as fast as I ever wanted it to dump, but there is a paragraph in the manual:

"4 Position bucket control valve type

This loader control valve has two stage dump positions. The first dump position by moving the lever to the right is the "Regular" dump position. It has good power and control for precise dumping. This position should be used when operating another implement with the loader's control valve. The second dump position (to further right) features greater speed for dumping. These two positions are separated by a "Feel" position for your convenience."

That paragraph did not emphasize "another implement" and certainly did not explain it as clearly as you just did.
 
   #5  

gerard

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dittos on the thanx kubmech - I actually understood it all!
 
   #6  

tbarber

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JD 855
So thats why my 87 JD 855 works like that ?
I didn't know why it was like that.
Tom
 
  
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kubmech

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Sure, one example on the "higher end" construction equipment you'll see regenerative circuits in, say the backhoe swing circuit due to the momentem created when moving all that weight to one side or the other. Now it is'nt as simple as what Kubota did (usually involves an added shuttle valve to draw from return oil to back feed into the circuit, which is a little tougher to explain). Not all regen circuits operate alike, but the reason for them and the out come is basically the same.
 
   #8  

glennmac

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For future Kubota reference, this $35 difference at the time of purchase will be closer to $400 if you want to switch to a 4-postion later on.
 
  
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#9  
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kubmech

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Excelent point Glennmac, I have seen this too many times, when somone has to add more "hydraulics" to their machine later on..........
 

billboe

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Kioti DK45SC w/ Backhoe
Great post/description Kubmech! One question (not that it matters!)... Why did you choose "buying/pricing" to post it?
 
 
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