Am I hurting anything?

tungularafishcamp · Oct 23, 2015

Have a Kubota l2800 with a backhoe. The hydraulic circuit for the backhoe is just looped when the backhoe is off so I put a two spool valve with quick connects that I had laying around along with a single action ram I had. I put it on only with the backhoe off and when I have extra stuff to haul. I use the ram for my top link and put my quick attach forks on back so I can pick up loaded totes of gravel, kelp whatever.

My question is when I am lifting the 3 point at max and it is limiting out whenever I depress the valve instead of letting the pressure out in the ram it sucks the ram in even stronger than when I pull the valve which normally sucks it in. If I have no pressure on the 3point then depressing it bleeds out the ram normally. It works handy and gives me quite a bit more lift than if I just use the straight 3 point lift. It has worked that way fine for a couple years but was just wondering if I might be screwing something up in the long run?

ch1ch2 · Oct 23, 2015

Good question. I too was thinking about putting rear remotes on like that when my bh is off.
I hope you get some good info.

bumperm · Oct 24, 2015

Interesting. I have a B3350 with B77 backhoe. In the instructions for connecting the backhoe, it *cautions* to make sure the 3 point lever is in the full down position and to leave it there while the backhoe is connected. And that doing otherwise can cause damage! The manual, like all good manuals, does not specify what damage, why, or how.

I have two Aux circuits on the back for top and tilt, so don't need to mess with the power beyond circuit, except to plug it back in when the backhoe is off.

tungularafishcamp · Oct 24, 2015

On the l48 I know you have to latch the 3pt down when the backhoe is on because the swing arms will hit the bh frame.

I couldn't find anything in the Manuel about it on th l2800

Carl_NH · Oct 24, 2015

On my B21 there is a push/pull lever which switches the flow from the 3PT to the BH valves and you loop the BH lines together like it sounds like you do. One time I removed the BH and forgot to move the lever and started the tractor basically this deadheaded the pump lugging the tractor down. I realized this immediately after starting so shut it down. Didn't hurt anything.

So if you aren't loading the pump/engine down when you are in 3PT mode with the valve/cylinder on the toplink I doubt you are doing any damage, and since you have been doing this for 3 years I believe problems would have manifested long ago.

I think the reason the top link cylinder is acting different when fully loading the 3PT lift is the pressure in the system and the larger area of the top link cylinder vs the 3PT lift cylinder the top link has the advantage?

muddstopper · Oct 24, 2015

Just trying to figure out what might be happening in the hydraulic circuit. If your cylinders are hooked in series, what you might be seeing is a pressure intensification event. In this type of even, the pressure on the cap end of the cylinder is increased because of the smaller area on the rod end of the same cylinder. If the fluid is just going to tank, than there is no pressure buildup on the rod end of cylinder, but if the fluid leaving the rod end of the first cylinder is passing thru the cap end of the other cylinder, the force applied in psi to the second cylinder cap end is greater than the force applied by the pump. Where this might cause a problem is where the second cylinder becomes under load and the pressure can build much higher than a hose or other components can handle. That pressure is not being relieved by the relief valve off of the control valve. Also if the cylinders are of similar size, the fluid exiting the cyl on the rod end, isnt great enough to fully extend the second cylinder to full stroke.

If the cylinders are connected in parallel, the cyl with the least load or biggest piston will move first before the second cylinder with the smaller piston or lesser load, but both cylinder will reach full stroke. This is sort of what you are describing and what Carl_NH is suggesting. One cylinder extending and one retracting might suggest a regen even where as pressure is equalizing on both sides of the piston and the cyl will extend. A cyl will never retract under regen. In order for a regent even to be occurring, you would have to have fluid bypassing somewhere in your system. Maybe a control valve not completely centered.