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....
