Backhoe problem

[2515R Dude]

BTW, I believe that the diagram you posted disagrees with the description of how you describe the flow in #2 above. It is hard to be 100% sure without a flow or schematic diagram - and without more details about the T part BY400-8800111.....but if it is a simple T....then the way I see it, that diagram doesn't show that the oil coming out of one cyinder goes to the other cylinder to help in the movement. That's good. It would be odd if it did.

It is a simple "T". In my opinion it does as i described. From the front of one cylinder the oil under the pressure escaped directly to the back of another cylinder and does not go to the tank. And as i see it, if there is air trapped inside, it will never escape and be play a role of a cushion till it pressurized enough till is able to transfer the pressure.

Is there any way i can check if there is air inside the cylinder?

My guess is that in each extension direction the combined expelled flow from the cylinders is returned back through the valve to the sump without any regeneration. Take another look and see what you think.

rScotty

I dont see how it goes to the sump. but again, i dont have any experience

 

[K5lwq]

It is a simple "T". In my opinion it does as i described. From the front of one cylinder the oil under the pressure escaped directly to the back of another cylinder and does not go to the tank. And as i see it, if there is air trapped inside, it will never escape and be play a role of a cushion till it pressurized enough till is able to transfer the pressure.

Is there any way i can check if there is air inside the cylinder?

This really is no different than your loader cylinders. The two lift cylinders are T off of one port as well as the two curl cylinders. The only difference is one cylinder here extends while the other one retracts. Air is purged the same way. Moving all the way from side to side will remove any air.

 

[rScotty]

It is a simple "T". In my opinion it does as i described. From the front of one cylinder the oil under the pressure escaped directly to the back of another cylinder and does not go to the tank. And as i see it, if there is air trapped inside, it will never escape and be play a role of a cushion till it pressurized enough till is able to transfer the pressure.

Is there any way i can check if there is air inside the cylinder?



I dont see how it goes to the sump. but again, i dont have any experience

OK. Indulge me. Look at the line going going from the top of the valve stack through fitting (21). It's the lower line....and lets pretend it is under pressure because of the way we have moved the valve. The flow goes to the lower T where it is split. The lower cylinder is pushed to extend and the upper one to contract.
The boom swings, and as it does the return flow is forced from the opposite end of both cylinders. That return flow |goes back through the upper T and then to the retrun channel iniside the valve and then to the sump or tank. .

It can do that because when you opened the valve to pressurize the fitting 21, it also opened a return port in the valve (not shown except in a schematic) which accepts the return flow and direct it to the sump. If you look at the drawing at the left hand side of the valve stack you will see a circle with the letter "T" in the middle of the circle. That is sort of hydraulic shorthand for the return to the "Tank" which is what some manufacturers call the sump. Drawings like this rarely show the tank or sump...and often leave out most of the return circuit as well. It's left to your imagination.

When you move the valve the other way, the upper line (21) is pressurized and everything reverses. The boom then swings the other way.

If there is any way to check for air I don't know it. I don't think it matters, and here is why:

You can see that one side of each cylinder is purely open volume. And on the other side of the piston in that cylinder there is a rod taking up some of the volume. Because the volumes are not the same, as as one cylinder moves in one direction the other cylinder cannot move the same amount. It will move either faster or slower depending on which way the valve is moved to pressure the system.
Moving freely, the movement will be dominated by the different volumes and internal friction of the two cylinders. Moving freely, the motion will show up as jerky motion until they are damped by a load on the rod end...and my guess is that a little air is handy as a cushion.

So those are my answers. I don't know how to tell air or if it matters. But suspect it doesn't matter on the pressure side of a hydraulic system. Air does matter on the suction side of a hydraulic pump where it is a big problem.

And it is pretty common for the return lines back to the Tank not to be shown in simple diagrams.
Even in a formal diagram - called a Schematic Diagram - return lines will only be shown if they have some function. Similar to the symbol for chassis ground that you see in electrical schematic diagrams.

Enjoy!
rScotty

 

[LD1]

That is definitely a pronounced pause in the video....assuming you were holding the lever the whole time and not letting off. (cant see your hand/valve movement in the video).

But something I would like to see you try....(even better if you can video it)

Do exactly like you did in the video. Start with the boom fully to the left. Start swinging to the right. AS SOON AS you see the swing start to hesitate.....immediately let off the lever.

Now get off the machine and manually try and swing the hoe from side to side by pushing on the bucket. If it moves back and forth any amount.....figure out where the movement is. (slop in pins and linkages....or are the cylinders actually moving in/out indicating there is air in the cylinders).

I have a theory of what may be happening to both the swing and boom....but want to know if you are getting air in the cylinders of the swing mid-cycle.

 

[2515R Dude]

To :K5lwq and rScotty - Yes, i understand by the diagram how it is supposed to work but due to my ignorance in tractor hydraulics i cannot see the whole picture where the problem could be, hence the only explanation comes from my experience with the automotive brake system - air in the system or leaking main cylinder -not enough pressure or loosing pressure.
Just try to apply my knowledge to the existing issue.

To LD1, i'll try two things today: a. To take a better vid and upload it. Yesterday i took 3 videos, but for some reason only the worst one left on my phone.
b. I'll try to check the air your way

 

[rScotty]

To :K5lwq and rScotty - Yes, i understand by the diagram how it is supposed to work but due to my ignorance in tractor hydraulics i cannot see the whole picture where the problem could be, hence the only explanation comes from my experience with the automotive brake system - air in the system or leaking main cylinder -not enough pressure or loosing pressure.
Just try to apply my knowledge to the existing issue.

To LD1, i'll try two things today: a. To take a better vid and upload it. Yesterday i took 3 videos, but for some reason only the worst one left on my phone.
b. I'll try to check the air your way, but i already can tell you, when i disconnected the rods from the backhoe and tried to pish and pull them in and out, there was some give/movement. They were not iron solid, but ill double check today just to make sure.

The difference is that the automotive brake system only uses hydraulic force to move one way. Backhoes (and loaders) have force in two directions - both extending and contracting.

In cars, the hydraullic pressure gives you braking, but there are outside forces (springs or impact) that move the shoes or pucks back the other way.

So automotive braking is only half of a backhoe system and doesn't have the two way pressure or fluid circulation like a tractor uses.

Air in the system??
Well, If there was enough air in the system to make a difference you would see it when you looked at the oil in the sump. The oil would be very foamy right after using the backhoe.

But you said in the post #1 , "The oil is on MAX, clean as teardrop, so no problem there."

If the oil had been foamy, I think we would have gone down a different track. Probably be looking for a dedicated backhoe swing pump with a suction air leak.

Just for info: The foamy oil will clear up overnight and look clear but gets foamy during use. Did we miss that? If oil is milky, then it has gotten some rainwater water in it. Watery oil stays looking ugly forever, but still works OK in the cylinders.

That is odd about the rod movement you can feel. For the reasons above, I don't see the problem as an air cushion. Is there any chance it could be the rod coming loose from the piston? A loose rod or some bad piston O-rings in thje swing cylinders is where we are headed now that switchng hoses on the valve stack didn't change things.

rScotty

 

[2515R Dude]

Another reason i'm thinking about trapped air is the connections to the cylinders not on the top of it, but on the side which theoretically can trap some air above the fitting. But again, it is my theory which is most likely wrong.
there are the pictures

 

[LD1]

What I am speculation being air....is similar to "floppy bucket" on a loader without a regen valve.

And its where some external force (usually gravity) causes a cylinder to move FASTER than it can be filled with hydraulic oil from the pump.

So in the case of the boom.....at full extend and LOWERING the boom.....gravity would tend to want to lower the boom pretty fast. And maybe faster than the pump can fill the cylinder with oil on. Which can cause it to draw a vacuum and/or suck air in around the gland seal. Which "may" result in what is happening.....but I havent seen a video of the main boom yet.

IT would be LESS pronounced on the other functions like the outriggers, dipper, and bucket because gravitational leverage against those cylinders isnt as great as on the main boom.

Now the head scratcher is the swing. But the way it is plumbed with a push/pull.....meaning with the Tee's, once cylinder is pushing under force while the other is retracting. Well because of the volume of the rod.....the cylinder that is retracting takes LESS oil to move a given distance than the cylinder that is extending.

Now under normal circumstances.....the one doing the pushing should require LESS psi because of the larger piston area. And hydraulics in TEE like to take the path of least resistance. So I'd expect it to be doing the bulk of the work and cylinder that is retracting is just along for the ride.

However.....with no load and sitting level....there is very little resistance to moving either....meaning very little pressure. So if the cylinder that is retraction is DRAGGING the extending cylinder along for the ride.....it is doing it FASTER than it can fill with oil....same as gravity acting on the main boom above.

In other words.....lets say it takes 1 pint of oil to make the swing cylinder RETRACT 6". Due to the volume of the cylinder rod.....that same pint of fluid may only EXTEND the cylinder 4".

So pump enough fluid that it retracts the one cylinder by 6"......thats only enough fluid to extend the opposite cylinder 4"......BUT they are mechanically CONNECTED so it has also moved the full 6". Hence the vacuum or drawing air in.

The above is just a WAG, as I am not there and only basing on what you have described so far. But if it is indeed something similar to what I have mentioned....the SLOWER the RPM of the tractor the worse the issue would be on the cylinders that are effected by gravity. Like the boom and dipper

 

[rScotty]

Another reason i'm thinking about trapped air is the connections to the cylinders not on the top of it, but on the side which theoretically can trap some air above the fitting. But again, it is my theory which is most likely wrong.
there are the pictures

I like your theory. Swing cylinders tend to sit horizontal and pivot at the end. So one could argue the port should be up on top where air would accumulate. I went out and looked at our hoes.... On the Kubota the retract port is on the side and the extend ports are on the bottom of the cylinder. Well, that seems odd.
It makes me wonder if that bottom port could have any bearing on why the M59 does have that occasional loss of swing force problem that nobody has ever figured out.

Then I looked at our JD 310. Uh oh... it has the swing ports on the side just like your Branson. An internet seach shows the same for the Case 580, other JD 310s, and the Cat 416 - as a group probably the world's best known backhoes. They all have the swing ports on the side. No Joy for the theory.

rScotty

 

[piper184]

Typically any air that leaks into a cylinder gets compressed under pressure then when the pressure releases the compressed air forms many little bubbles instead of one big one. This allows the fluid to hold the air and carry it out of the cylinder on the next cycle. I think this is one of the things that fluid chemist strive for. At least that is my understanding.

Interesting thing about the swing cylinders is that my BH only has single acting cylinders for swing. They are plumbed to the valve as if it were one double acting cylinder. So in this case there is no difference in cylinder volume from extend to retract. There is also only the push from one cylinder and no "pull" provided by the other one. Trade offs...

One other thing to consider when observing speed changes of the swing is the pivot point geometry. As the rod end extends past the center line of the boom pivot the effective distance from the rod end to the center pivot gets shorter. Even though the rod is extending at a fixed rate, the rate of rotation of the pivot changes. This will be most obvious when the bucket is out all the way. Perhaps this is what Branson was referring too when they said it was normal.

If you could figure out a way to measure rod travel speed and compare that to swing speed you could tell if the slow down was caused by the cylinder or the geometry of the pivots. I'm not very good at explaining these things in writing. If I confused you let me know and I will try to make some drawings. I am not familiar with your exact BH so some of this is just a generalization.