LS tractor bucket flop problem

[oldnslo]

LD1 s correct on the air getting drawn into the cylinder but it is not drawn in around the rod seal.

When dumping a load the rod end is under pressure created the induced load of the bucket. This induced load forces the oil out of the rod end faster than the pump flow rate can fill the cap end. This causes a vacuum in the cap end which leaves an air pocket in the cap end of the cylinder.

Some ways used to fix or reduce this happening.

Regen spools: Like LD1 states these do not vent either cylinder port to tank so now the pump only has to replace the volume of the cylinder rod.

Flow controls or orifice: These will also reduce the flop if sized or set properly but have there limitations since they are fixed restriction. Changing the load on the bucket, RPM's of the engine, etc. will chnage the amount of restriction required.

A spool designed to meter flow out of the rod end while allowing flow into the cap end is also an option used on larger more expensive equipment. These spools have asymmetrical flow rates which help prevent the runaway load.

Counterbalance or brake valves: These require a constant pressure to allow oil to pass and and be different pilot ratios to limit the brake effect.

 

[Cataclysm]

I will check and see. Would a pic of the valve help?

 

[LD1]

LD1 s correct on the air getting drawn into the cylinder but it is not drawn in around the rod seal.

When dumping a load the rod end is under pressure created the induced load of the bucket. This induced load forces the oil out of the rod end faster than the pump flow rate can fill the cap end. This causes a vacuum in the cap end which leaves an air pocket in the cap end of the cylinder.

Dont take this the wrong way as I am not looking to stir things up or have a debate, as I know you know more than most on this forum when it comes to hydraulics.....

The rod end isnt under pressure when dumping, as it is open to tank and just "flowing". only pressure is just the resistance in the lines for that oil to return to tank.

Hydraulic fittings and hoses seal against the hydraulic pressure as well as air/vacuum. the air that gets into the system can come from anything not designed to seal against vacuum. That would only be tank vent and rod gland lip seals.

If air getting in there under vacuum is not coming from the rod seals, where do you believe it is coming from? (dont really have any way to prove one way or the other, and I honestly dont know, as it really doesnt matter where it comes from, as long as you know its there and how to address it)

 

[LD1]

I will check and see. Would a pic of the valve help?

Pic of the valve wont help much. But if there is a sticker/diagram near the valve that shows the loader functions......or one in your manual that explains the functions.

 

[oldnslo]

Dont take this the wrong way as I am not looking to stir things up or have a debate, as I know you know more than most on this forum when it comes to hydraulics.....

The rod end isnt under pressure when dumping, as it is open to tank and just "flowing". only pressure is just the resistance in the lines for that oil to return to tank.

Hydraulic fittings and hoses seal against the hydraulic pressure as well as air/vacuum. the air that gets into the system can come from anything not designed to seal against vacuum. That would only be tank vent and rod gland lip seals.

If air getting in there under vacuum is not coming from the rod seals, where do you believe it is coming from? (dont really have any way to prove one way or the other, and I honestly dont know, as it really doesnt matter where it comes from, as long as you know its there and how to address it)

LD1
Agree don't want to start a debate but if you put a gauge on the rod end of the cylinder when dumping it should never read a vacuum unless you have some super high velocities. There is always some pressure required to force the oil out of the cylinders, through the lines, valves, etc back to tank. The air is in the blind or cap end of the cylinder caused by the vacuum in that end. The air is drawn out of the oil and or possibly through the fittings on the cap end. The amount of air depends on so many factors it is hard to even calculate. Some of these factors are:

Splash in the reservoir / transmission. The gears turning in the oil cause some air to be entrapped.

Oil temperature: As the oil temp varies so does it potential for holding air. As oil/air heats up they expand.

feathering or flow restriction. Flow restrictions also cause air oil separation this may be happening at the valve.

110% agree this is a difficult concept to explain and grasp.

 

[George2615]

Does the LS have a regen spool on the dump circuit?

When dumping the loader, you are basically opening the rod port to tank, and pumping fluid in the base port by the pump. Well, the only thing keeping gravity from taking over is whatever vacuum the rod seal can hold back, which aint much. So the result is, gravity dumps the bucket and expels the fluid out of the rod side faster than the pump is filling the base end, so the result is air gets sucked in around the gland seal. Now you have a floppy bucket.

In regen mode, it dont open the rod port to tank. Instead, it also gives it pump pressure, so both ends of the cylinder get pressure. This keeps air from getting sucked in and will keep the bucket from getting floppy. In the manual, it would be listed something like fast dump.

The key is to find out if your tractor has regen, and if so, is it the first position of the lever, or second. On my kubota, regen is the first position. I have heard on some others and on aftermarket valves that its the second position. That would be odd for me as I am not used to pushing the dump all the way.

I'll check it this weekend. As far as I know it does not have regen or what I called fast dump as my other tractors had. I'll try the dump mode slowly and see if it stays in place. As it is now, if I angle the bucket down say 10-20 degrees using dump mode to back drag then put the loader in float mode, when the bucket touches the ground it will go back to almost flat bottom due to no pressure holding it in place. Then I have to hit dump mode again to force the bucket to stay at the desired degree to back drag.

I think it is a trait of all LS tractors and a few other brands. I only started this thread because myself and many others have questioned why it does this and what would be the cure. My joystick is cable operated to the spool. All previous tractors I've owned or used had the joystick attached directly to the spool valve.

 

[Cataclysm]

No fast dump here. Checked the loader operation diagram and tried to fast dump.

 

[LD1]

Are you saying the loader diagram don't show fast dump? Or you just aren't noticing it dump any faster.

The detent on some valves is very subtle and almost non existent even though it has regen.

You may not notice a difference in speed because gravity causes it to dump fast even in slow mode...so fast it causes air and thus the problem.

Course, it may very well not have regen either. If that's the case, it's just the nature of the beast.

Have you tried putting the bucket flat on the ground and dumping to the desired backdrag angle (while simultaneously lifting) to prevent gravity from pulling the bucket open faster than fluid can fill? That should result in a less "floppy" bucket

 

[George2615]

Are you saying the loader diagram don't show fast dump? Or you just aren't noticing it dump any faster.

The detent on some valves is very subtle and almost non existent even though it has regen.

You may not notice a difference in speed because gravity causes it to dump fast even in slow mode...so fast it causes air and thus the problem.

Course, it may very well not have regen either. If that's the case, it's just the nature of the beast.

Have you tried putting the bucket flat on the ground and dumping to the desired backdrag angle (while simultaneously lifting) to prevent gravity from pulling the bucket open faster than fluid can fill? That should result in a less "floppy" bucket

Loader joystick diagram does not have fast dump.
Diagram shows joystick positions for loader up, loader down and float, curl up, and dump. Joystick can also be moved diagonally for lift and curl or lower and dump dual function operating.

Another member posted a video of his LS although I don't remember who nor could I find the thread (A sign I'm getting old and suffer from CRS) showing he raised the loader arms and put the bucket in dump mode, then got off the tractor and walked up to the bucket and with his hand could push the bucket back and forth like there was no pressure in the cylinders to hold the bucket in place.

 

[Cataclysm]

Right, the loader diagram doesnt show a fast dump. And slowly pressing right on the stick to all way is s short even travel.

Just to be clear I have no issue with the loader control. Its a small tractor and they all have their personalitys.

To backdrag after dumping I just leave the bucket down and drop it into float and adjust from there.