My quest for "Grand" 3 point performance from my "economy" tractor. The L3400

[Harvest Moon]

Re: My quest for "Grand" 3 point performance from my "economy" tractor. The L3400

Good though ht1.

I'm starting to discount my theory that it's the spring. Not that the spring isn't important but that other components make the difference. With all this talk about flow restriction I'm questioning how a spring held in place by a retaining spring clip could possibly be stiff enough to provide enough shock absorption to influence fluid pushing at over 2000 psi.

The washer, slowing things down, seems to make more sense.

I don't understand enough about how these things work. How much spring resistance would it take to absorb sudden 2000 psi + pulses of hydraulic fluid?

Then again, having a spring in there, even fully compressed, would limit the full range of motion of the adjusting collar by a significant amount, which also may limit or slow the flow. The adjusting collar appears to be the "check" component of the valve.

 

[ht1]

Re: My quest for "Grand" 3 point performance from my "economy" tractor. The L3400

harvest moon when is your part going to be in.

 

[Harvest Moon]

Re: My quest for "Grand" 3 point performance from my "economy" tractor. The L3400

I pulled the original valve today. Except for care to avoid a spill and some concern about the amount persuasion needed to pull it out, it's really a 5 minute job. Didn't loose any fluid except what dripped off the valve. 12 mm wrench, a few paper towels and 1"x1"x12" oak lever is all it took.

I took apart the business end of the valve and it's definitely a check valve with a limiting adjustment to allow the hitch to fall at a selected speed. If we could reverse its function we could slow the rise with the knob. Ultimately this valve could be modified to have a smaller port and a slower rise. But that is beyond my determination and would require a good machinist.

My optimism took a hit when I saw that the port the fluid passes through is already fairly small and the theory on the washer slowing the flow is nearly useless. It would be easy to put a blank in to replace the washer with a predetermined hole size but I fear the spring clip could fail under the pressure and let the components burst into the cylinder. Not a risk I can afford.

Thanks to a post by jfay regarding the resistance of the relief spring being somewhat compressible I still hold hope for the original spring theory but again, how stiff could it be, being held in by a spring clip. The port in the valve is solid cast metal and looks like it was designed to handle 3000 psi. The spring clip doesn't look like it could handle 50 psi of force against it. My latest hope is that the spring keeps the check from slapping and flopping around in there more than anything else and results in smoother function by default.

I doubt anyone will ever convince me that there isn't a reason the valve on the more expensive and better performing tractor has a spring but today I can't really see how it will help us with the L3400 and L2800.

I'm almost reduced to my original observation that several other Kubota models that have this valve have better performance with the same PCV as the L3400.

Here are some photos of the valve and one of it's home.



I'm expecting the new valve soon, between Monday and Wednesday. It should not take more than 5 minutes to install, although if it goes back in as tight as it came out it might be a little disturbing.

 

[Harvest Moon]

Re: My quest for "Grand" 3 point performance from my "economy" tractor. The L3400

The thing with the 4 holes in it in the third picture is called the adjusting collar.

What you can't see is that the other side of it has a cone shaped top to it. This cone acts like a floating needle valve, when the flow is reversed to lower the hitch this cone tries to block the port in the valve. The external knob adjusts a pin that restrains the cone on the adjusting collar from fully seating unless the valve is set to the lock position.

 

[EE_Bota]

Re: My quest for "Grand" 3 point performance from my "economy" tractor. The L3400

I hate hydraulics. You need x-ray vision to see what's happening. And everybody has problems with it, and even though it can be calculated easy as pie, nobody has all the information you need to do the calculations.

And even though the concepts are easy as pie, your eyes roll back in your head trying to apply them to failure modes. There are never enough test ports, and you always seem to wind up with the wrong size fitting somehow.

I spent all day trying to help a buddy with his M-F, and I have a raging head and neck ache....literally.

But here goes on your problem.

Unless your control valve is designed by a pervert we must consider what causes jerks.

Jerks can be caused by stored energy...entrained air, flexible lines, even bouncy tires. If your tires are properly loaded with fluid, much of that bounciness is eliminated. You can't do much with hoses except make sure that are no longer than necessary and pretty rigid with good wire in them. Make sure your lift cylinder is properly bled of air, and be sure that your fluid is not becoming filled with air bubbles.
This will store energy, and it will help you out when the lift is trying to go up (store/buffer some of the jerk) but release it with an over-travel at stop time, which could be causing a position feedback mechanism over-reaction resulting in a quick drop. Think about it... you fellows are setting up oscillations.

Other than that...everyone always remember...pressures causes force, flow causes speed.

Your jerk could be just a FAST lift caused by the lift pump being too large relative to the lift cylinder size. If this is the case, then reducing the flow will help a great deal.
But remember, if the pump is fixed displacement, then the flow will insist on going somewhere. The least it will do is heat something up. The most it will do is ruin something very expensive.

So you can't reduce the flow with a restriction because the flow INSISTS, so
a restrictor that reduces the flow by half will make half the flow pour out through the pressure relief valve, or the pump will shatter, or the engine will stall. This means a lot of the hydraulic horsepower will go towards heating your pressure relief, a fraction will go toward heating your restrictor , and a fraction will go toward raising the lift.

But imagine this:

If high flow is the problem, and the pump is fixed displacement, then is there any engine rpm (therefore flow) where the jerk is acceptable. If so, write that rpm down. Compare that to the max rpm you are likely to want to run your engine while doing 1/4 inching lift movements...and see if you can tolerate at least half of full flow. If you can....

I know nothing about your tractor, and have not looked at the schematic, but I probably will after I get the Massey going...but someone said something about an accessible supply line. If you can replace that line with one that has a very good and easily replaceable variable pressure RELIEF valve, followed by a variable flow control valve, you may safely reduce the flow (if flow is the problem.)
The relief valve must be high quality so if it bleeds at set psi psi, it does so smoothly and the line being bled is still at a smooth set psi. It can't set up an oscillation.

The idea is to set the external relief 10% below your pump relief so you external relief takes the beating instead of the internal relief. You will have pipe the oil relieved back into the tranny, perhaps through a filler hole, provided internal flow channels can return it safely to the tranny without aerating it too much. Usually it is desired to return oil below these fluid level if possible.
Anyway...I could be wrong....and I do hate hydraulics...so don't take my word for it....

 

[canoetrpr]

Re: My quest for "Grand" 3 point performance from my "economy" tractor. The L3400

I *think* I know a good place for an flow restriction and an external relief valve as has been suggested by EE_Bota.

There is a hydraulic block on the right side of the tractor - under your right foot. There are three 'ports' there. One is the OUT to the loader, one is a TANK and one is the PB. The PB port is where pressurized fluid that is unused from the loader (or rear remotes if you have them) goes back in to feed the 3PT valve.

The 3PT valve is the last valve in the circuit so there is no other valve between this PB port and the 3PT valve. The flow could conveniently be restricted right here and a external relief valve could be easily added here.

Now, I don't know squat about hydraulics. All I do know is that from talking to MadRef (RIP), he suggested 1/4" hoses for my top and sidelink cylinders - when I was installing my rear remotes - to reduce the flow - to allow finer grained control of the cylinders. That is sorta where I got the idea for a flow restrictor.

The one thing that I don't quite understand is that if the flow was restricted here (at the PB port) - would there be any impact to the lift capacity? I think the answer is no - so long as the appropriate pressure can be maintained while the cylinder is being activated. What EE_Bota said which brought the point home to me is that what I need to worry about is quite the opposite. That is is important to note is that restricting the flow will increase the pressure as you have the same amount of fluid going through a smaller inlet. Now, I don't really think that a relief valve is absolutely necessary here as the components are generally overbuilt a reasonble amount - but it is the safe thing to do as EE_Bota points out.

I believe that there is a REALLY simple solution to our problems and it is as follows:

- Identify which of the three ports on the hydraulic block is the PB from the loader. This is easy to do. If you look at your loader valve you will see a PB being labeled. I believe it is also covered in the owners manual. I'll know as soon as I look on the tractor as I will remember from when I installed my remotes.

- The hyd fitting from the hose that fits on to this from your loader is a 3/8 JIC female. The PB "port" is a 3/8 JIC male. All you need to do is to add a flow restrictor HERE. I think you can get fittings that are meant specifically to reduce flow - I remember reading about it on a thread. I don't know what they are called. A poor man's flow restrictor will be a 3/8 JIC male by 1/4 JIC (male) fitting hooked up to a 1/4 JIC (female) by 3/8 JIC female. You put that fitting between the hose that comes from the loader's PB port, and the hydraulic block. That way the fluid that feeds the 3PT has been flow restricted - just like MadRef (RIP) suggested I do for my top and side link cylinders for fine grained control.

- For safety, you add between the flow restrictor fitting I described above, and the hydraulic block, an external relief valve shunted to to 2500 psi.

- Voila! Now the 3pt should work smoothly.

I'm feeling pretty good about this theory and I am sticking to it! To test it out, the fittings are quite cheap so I will test it out when I have a chance. Might not add the relief valve just for the test.

I think 10 dollars in hydraulic fittings applied between the PB return hose from the loader to the hydraulic block will smoothen out the 3PT for us. Lets see if it hangs together!

I think that the answer was sitting right there given MadRef (RIP) had show me EXACTLY the same solution to get EXACTLY the same result - i.e. feathering ability but on a different cylinder. I'll bet he will be smiling upon us if this works out

 

[Harvest Moon]

Re: My quest for "Grand" 3 point performance from my "economy" tractor. The L3400

Harvest - you are DA MAN for taking on this effort. The rest of us will be watching keenly.

Who's DA MAN now canoetrpr! Now I'm watching keenly!

I knew it was a mistake when I titled this thread "My". If we don't figure this out I'm fine to leave it "my" but if this thread leads to a solution, we'll have to find a way to change it to "the" or "our". teg, we got our fist hydraulic guy and maybe thanks to your request!

Wow, thanks for the input EE_Bota. We can use as much as you're willing to share and I think there are more than a few of us watching. Anyone who has a clue or theory about these things, please, chime in.

My question now is, would restricting the flow to something that probably has a "duty cycle" of less than 10% necessitate an extra relief valve? I don't think, under the heaviest use my 3 point's ever run more than 20 minutes in an hour and not continuous. Half the time has to be spent lowering without activating the relief anyway so 50% is the max it could even tickle the relief. There's a lot of fluid and a cooler somewhere to dissipate the heat. And this is meant as a question, not to argue against a relief.

On the flip side, nearly every time I attempt to scoop a bucket of my sticky heavy clay I activate the relief via the loader. Not to mention every time I operate it to its range of motion limit. I'd bet I've run the relief 20 minutes out of an hour on regular occasion.

canoetrpr, I was studying the "HYDRAULIC OIL LINE(DELIVERY)" from the "hydraulic block" and observed that it is connected to the hard line by something of a bolt with a hole in it referred to as a "joint." I was thinking a bolt/joint with a smaller hole might do the trick. Your fitting thing sounds perfect but I'm not exactly visualizing it from what I've seen in the parts book. I'll have take a look at the tractor with the loader hooked up.

 

[canoetrpr]

Re: My quest for "Grand" 3 point performance from my "economy" tractor. The L3400

Harvest:

I think the main thing that EE_stor was pointing out to us is that if you take fluid flowing through a 3/8 line - as all our hyd lines are - at a given PSI and then restrict it - e.g. through an orifice or my el cheapo suggetion of a 1/4 fitting, the fluid coming out of the other side will have higher pressure - I *think*.

The same amount of fluid is trying to get through a smaller area.

Much like if you put your finger in front of a garden hose you will increase the pressure of the fluid coming out but decrease the total amount by a bit given the inefficiency that has been reduced in the system - i.e your finger restricting the flow.

So the concern is that the lines that go from the PB port of the hydraulic block under your right foot, to the 3PT valve and the 3PT cylinder then, will be running at a higher PSI as a result of the restrictor.

Now as I write this, I realise that with the suggestion I made, the pressure should drop again as the fluid comes out of the 1/4" fitting and goes back into the 3/8" fitting. The 1/4" fitting simply acts as an obstruction that is seeking to restrict the fluid flow at one point in the system. Since we are not replacing the lines from the PB port of the block all the way to the 3PT valve and cylinder, nothing else other than the 1/4" fittings should be exposed to more pressure than the relief of the tractor is setup to.

What we are counting on is some loss of kinetic energy of the pressurized fluid going from the hydraulic block to the 3 PT valve.

Now I have not looked at the hydraulic diagrams but I expect that the relief valve of the tractor is in series, between the hydraulic pump and the first valve in the circuit - which would be the loader in our case.

I think that a similar thing could be achieved instead by simply adding an external relief valve on the PB port of the hydraulic block, shunted at a PSI LOWER than what the rest of the system is running at. The problem with this is that we would now loose a bit of lifting capacity of the 3PT.

Again - I don't really know squat about fluid dynamics. I am a electrical / computer engineer and its been a long time since my first year eng. courses so what I really ought to do is read up on the subject before I do anything else.

What I think we are REALLY missing in the system, is a 3 PT cylinder that is of a wider diameter. We are trying to work around that problem using a cheaper solution using a undersized fitting to obstruct the fluid flow.

 

[8934]

Re: My quest for "Grand" 3 point performance from my "economy" tractor. The L3400

I have worked for a dealership, and a large OEM in their R&D department. Based on my experience manufacturers often obtain parts from multiple suppliers to prevent a strike, fire, or natural disaster from completly shutting down production.

The differences you are seeing between different models may be a result of slight differences between different part makers.

Good luck in your quest

 

[Reg]

Re: My quest for "Grand" 3 point performance from my "economy" tractor. The L3400

Good grief Charlie Brown, is Kubota support really SO BAD that they can't 'fess up to this and provide a solution ?
They HAVE TO KNOW about this (internally, within their corp support org).
Even a kit of parts solution with a discalimer about voiding the warranty ?
OK, so SELL the kit of parts if they're that strapped for cash.

Ahh, fergit about the warranty - on the parts of the tractor that don't work right it is already useless.

Seems to me this is a DESIGN problem, there HAS TO BE support documentation for a fix, even if it is (/was) a phase into production fix.
Make it a service/repair option, or whatever they want to call it.

Who, me ?
No, I don't care one way or the other.
'cept that it is a simple servo mechanism that SHOULD be simple to understand and SOLVE without owners having to resort to speculative parts swapping.