How are dual backhoe swing cylinders plumbed?

[rebeltect]

I'm curious and I can't find the anwser anywhere :confused2:!!! On backhoes with two swing cylinders how are they plumbed so that when one pushes the other one pull's? I feel like it shouldn't work, being plumbed into the same control circuit. Is there some sort of splitter or equalizer valve?? Also is having two cylinders on the swing even necessary?

 

[jenkinsph]

If you connect base end of one cylinder so that the fluid is extending the rod with a tee and run the other side of this tee to the upper end of the second cylinder so that it will retract you wind up with a push pull motion. The second hose does the same with the two remaining ports.

 

[Arc weld]

Switched ports will automatically equal out the pressure so they work in unison.

 

[rebeltect]

If you connect base end of one cylinder so that the fluid is extending the rod with a tee and run the other side of this tee to the upper end of the second cylinder so that it will retract you wind up with a push pull motion. The second hose does the same with the two remaining ports.

Switched ports will automatically equal out the pressure so they work in unison.

Thanks alot jenk & Arc, this makes sense, for some reason I didn't think it would work like that :duh:. Do you think that it's necessary to have more than one cylinder on a backhoe swing?

 

[BukitCase]

Assuming a 3" dia. cylinder with a 1.5" dia. rod, the difference between push and pull in a 2000 psi system is approx. 1500 pounds - no biggie if you stick to just moving the swing under no load, but if you use the SIDE of the bucket to push spoils back into a hole, you'll want all the "swing power" you can get - my old Case 580 has dual swing cyl's that are at least 4" diameter, and there are times I wish they were bigger, at least for what I just explained.

Also, keep in mind that most swing setups are a pretty short "lever arm" - IOW, not a lot of mechanical advantage in their geometry. So any lessening of available force going one direction vs. the other would be more noticeable... Steve

 

[J_J]

It would be interesting to put a hyd gage in the swing cyl circuit and see what the pressure is.

I am assuming that a hose connects the base end port of one cyl and the rod end of the other cyl port.

The side of the cyl with the largest surface area should generate more force. But then again, the total surface area would and generate a certain force.

Both cyl would develop a combined pressure?

One cyl might swing the boom if the geometry is right.

 

[dfkrug]

Do you think that it's necessary to have more than one cylinder on a backhoe swing?

Not only are 2 cyls not necessary, many older attachments (Woods, Kubota, etc.) use only one double-ended unit
along with a chain that wraps around the boom's pivot. This design is getting rare now, as it is generally inferior to
having 2 cyls.

The hard part of designing the swing system is how do you get a full 180 degrees of swing? You can't do that
with a simple one-cyl design that uses a moment arm on the pivot. 2-cyl designs near the swing limits have one
cylinder push the other over-center. Hard to describe....pix needed.

 

[Tor Arne]

If I remember correctly Ford had a patent with hydraulic motor on the swing with chain. Have also seen a solution where the house of the hydraulic motor acting as attachment to the boom and cylinder , it had a shaft that went through the motor and was attached to the tractor at both ends

 

[BukitCase]

The Case hoe is the only one I'm that familiar with (in some cases, TOO familiar )

My swing cylinders are trunnion mount, which helps the geometry for a full 180 deg. swing - it also will REALLY hurt the POCKETBOOK if they need replaced, as do the loader bucket curl cylinders (same type mount) - last I checked, a replacement cylinder for the loader curl is at least $800 if you're lucky, haven't priced the ones for the hoe swing.

BTW, Case is the only mfg I've seen that uses trunnion mount cylinders on their loader curl - They use extra "bell crank" (sorta) linkage so that to CURL, the cylinder PUSHES - this gives maximum breakout force while digging without having to go to a 4" cylinder to compensate for rod displacement during retract mode. Hard to describe til you see it, but definitely makes a difference.

JJ, you're correct on the plumbing on dual swing cylinders - because the push on one is effectively teed to the pull on the other, the hydraulic pressure is the same in the push cyl. as it is in the pull cyl. - the only difference would be the force applied OUTSIDE the fluid path, and with one pulling and the other pushing, you get the SUM of the two forces applied to the boom swing, each to it's own pivot point... Steve

 

[bcp]

BTW, Case is the only mfg I've seen that uses trunnion mount cylinders on their loader curl - They use extra "bell crank" (sorta) linkage so that to CURL, the cylinder PUSHES - this gives maximum breakout force while digging without having to go to a 4" cylinder to compensate for rod displacement during retract mode. Hard to describe til you see it, but definitely makes a difference.

Push to curl:



Bruce