How are dual backhoe swing cylinders plumbed?

glastron23 · Apr 28, 2014

worked on most of the systems, the dual cylinder type is by far the most common... the force from both cylinders are added together for the total. 2000psi on a 4 inch cylinder (25000 lbs) with a 2 inch rod (18800 lbs pull) for a total of 43800 lbs total...
The Ford motor style (several others used it also JCB Massey and some other off shores) as a good idea but was a BIG pain to keep sealed and the power levels were just not there.. ford pumped the idea and used a chain style so as to hide the cyinders.

BukitCase · Apr 28, 2014

Bruce, thanks for that - mine's a 580B, looks like the C went to a cheaper to make self-leveling method. Mine uses a "passive" cylinder that's attached near the main loader pivot - as you raise the bucket, it extends the cylinder which re-distributes the hydr. fluid to the curl cylinder circuit, changing the bucket tilt to compensate for loader geometry.

Seems to work OK, but to me it's just one more cylinder to rebuild (7 down, 6 to go

)

Sure wish I could find an adjustable pin spanner that was herky enough to survive getting the gland nuts loose on these durn Case cylinders after they've been in use for 40 years - the last one I had to collapse the cylinder completely to get the piston as far away from the gland as possible, clamp it in a 6" vise, heat about 2" of the gland end cherry red with a torch, then grab its 1/4" wide flange with a 36" pipe wrench and try to dislocate my shoulder before it'd give up

Of the 6 left, one loader curl cyl. pees like a racehorse, one of the two boom cyls drips a little as does the dipper. Others may wait till he** freezes over or I die, whichever happens SECOND

Still, even with the maintenance a backhoe sure beats the crap outa using a pick and shovel - moreso with every day I get older... Steve

Glastron, you posted while I was typing - I agree about the force - I've used my old 580B to push trees over - some up to 8 inch I've just put the hoe bucket on one side of the tree and swung the boom a couple times on each side, and out they come...

Brad_Blazer · Apr 28, 2014

On my old ARPS 730 there are two 2" pitch chains connected to single acting cylinders that pull in opposite directions. They are plumbed just like opposite ends of a dual-acting cylinder. I think the advantage of this setup is constant velocity in both directions.

BukitCase · Apr 29, 2014

"I think the advantage of this setup is constant velocity in both directions. "

Brad, I don't notice any change in swing speed through its range with my Case, although I've not actually measured it - it's just not enough to cause me to think about it.

From your pic, I'd say the main advantage to your swing setup is simpler geometry while still getting enough rotation - the design gets much easier if the last foot or so of each "rod" can wrap around like your chains - and even though this means you only have the LESSER of the two forces for any given cylinder (the retract force) that method wouldn't work if the cylinders tried to PUSH as well (ever tried to push a wet noodle somewhere it didn't wanna go??

... Steve

LD1 · Apr 29, 2014

Tho da cylinders with one pushing and the other pulling are also equal speed. And they are both needed indeed in my experience.

My old ford 5500 has dual 4" for a total force of 44k or so as noted above. But that's only a 20" or so stroke cylinder. My how has a reach of about 22' and can swing 185 degrees. Without having a calc handy, that's somewhere around 70' of movement. If the cylinders had a 24" stroke, that's a 35:1 ratio. So now that 44k of swing force is only like 1300-1400 at full reach.

Dads 4500 has a swing chain. So it has dual cylinders that pull only. Cause its hard to push a chain. But it also has a shorter reach.

granitepeak · Feb 11, 2020

jenkinsph said:
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.

My current setup has 2 obsolete double acting cylinders that have 3 ports. With 2 ports side by side for the lower end, I assumed that it was the equivalent of a tee as one port crossed over to the the other cylinder upper port.

I had thought using a tee would work with new double acting cylinders, but was told by Prince Hydraulics that the volume of fluid is different on each end of the cylinders and that I should run a hose from the top of cyl 1 to the top of cyl 2 and then go from port 1 on the valve to the lower right and port 2 on the valve to the lower left. While I can see that working, I was concerned that the upper end of the cylinders would be running dry and that would create issue.

So with one cylinder having Y capacity on the lower and Z capacity on the upper, will it balance out with a tee?

Thanks,

Don