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

Anyone out there have the ability to provide the diameter of the cylinder in the L3400 and the diameter of the L3010 cylinder for comparison? It would be nice to confirm that as a factor of the difference in reported performance between the two tractors.

According to TractorData.com the L3010 has a rear lift of 3090 lbs., if that is true I'd bet it does have a larger cylinder. But 3090 lbs. sounds higher than what I'd expected and may not be accurate. For example a new L3240, according to Kubotas specs. only lifts 2646 lbs. Still 1000+ over the L3400. But it has a 2 gpm higher flow to match.

For the L3010 I'd think the higher system pressure probably reduces the size requirement some but I'm not sure we yet know. Can anyone confirm the L3010's lift capacity?

I would expect the L3010 has a more powerful pump to match the lift and pressure but maybe a better pump to cylinder ratio than the L3400?

 

[teg]

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

"...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 I remember, it's jerky either way, can someone confirm this?

I was wondering if some units would have trapped air pockets... until 8934 mention about parts coming from several sources... probably not created equally. IS there some owners that have smooth non-jerky action on their 3ph???

 

[EE_Bota]

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

I am old school and I take it to be literally true that if you block any of the flow, the system will immediately go up to relief pressure due to the fixed displacement pump. However, if you do not block any of the flow, the implement movement will not change or move at a different rate, and hopefully with less jerkiness.


Canoe_ EE's usually do the hydraulics in factories, not ME's.
So, if ya have to, ya have to. So I'll give my opinion of what the circuit would look like, but in the end, you must use the REAL circuit.

The pump is fixed displacement I assume, with a fixed relief valve.

This is a constant current source with a zener diode to regulate the voltage which is in parallel with the pump branch. The breakdown voltage of the diode is system relief valve pressure.

The restricter is a resistor. Its resistance is either what we set it to or what we are allowed to set it to.

All other resistances are lumped into our restrictor resistor.

The lift is probably a motor, but we don't have to deal with that necessarily.
The know that the sum of the pressure drops (voltages) around a loop is zero, therefore if we knew the voltage (pressure) of the lift cylinder, we can figure out the voltage (pressure drop) across the restrictor.

The lift cylinder pressure (voltage) will be different for each implement, but for a given implement, it is the cylinder pressure that is required to barely start the implement moving up at the part of the stroke that is least mechanically advantageous. One can simply move the implement to that part of the stroke and measure the pressure statically, but margin must be taken to account for hysteresis.

The reason I said variable relief and variable flow control valve is because there is no way you will know all the variables to calculate everything directly. I feel way down in my left leg that a fixed orifice will not work for all implements. My gut chimes in that a heavy implement that approaches the lift capacity will either a)move dreadfully slowly or b)be just as jerky as ever
and I believe this will be your choice by how you adjust the valves.

But even though I said you cannot know all the variables, it is worth trying to solve the actual circuit because even with unknowns you will see where the limits lie.

And although I said implements approaching lift capacity will not be helped, some of the lift capacities are pretty high, so you may never approach them.

 

[canoetrpr]

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

EE_bota - I LOVE that EE explanation of the hydraulic circuit! I've been doing software ever since I got out of school 10 years ago so these days I am an EE in name only

I was at the local Princess Auto store's hydraulic section where I was chatting with the guy at the counter and he pointed the same thing out to me - which is what you want is flow control that is pressure equalizing. They had such entities in stock. Some had a built in relief valve, others were still pressure equalizing but did not have he relief valve. His opinion was that I did not NEED a relief valve per se as long as the system had another relief because these gizmos would ensure that the pressure at the out was equal to the pressure at the in and excess fluid would come out to a return which needs to be sent to the tank.

I am in complete agreement with you now that what is required is variable flow control. The units they had in stock that could manage 10 GPM (our tractor is 5-7) was large enough that I figured I would come home and first see where it could be mounted on the tractor and then look into purchasing one.

 

[canoetrpr]

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

Here are some flow control valves that will do the deed:

1. Surplus Center - This one has no built in relief - 0 to 8 GPM

2. Princess Auto - Go the "Hydraulics" section and go to page 24 and look at the bottom.

The Princess Auto one at 16 GPM will work and it has a built in relief valve. However we don't have a 16 GPM system. The one from Surplus Center might be smaller since it is rated for lower flow. I will measure the Princess Auto one.

At this point, I'm not sure whether a relief is necessary or not but one can certainly be added to the SC valve above. I did not find any appropriate SC flow control valves that had a built in relief.

 

[EE_Bota]

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

I was talking about a single flow control valve, which is a simple variable orifice. What you are proposing is a much more complex valve, with totally different rules. Looking at the surplus hydraulics one, I would be tempted to try the simplest non relief one. It seems to actually be a flow divider, and will send excess flow to tank, which is essentially what I wanted the pressure relief to do.

I do not understand the valve, however. If you look at the specs, a pdf can be downloaded that explains it fairly well. There is only one think I didn't like/understand about it.

It says "Please note, if during operation the CF (controlled flow) port is blocked, the valve will compensate in such a way as to block the excess flow port"

What do they mean by blocked? What will happen in this state?

Are we talking complete blockage here like a trying to move a boulder. It is something you could accidentally do with the control handle of the prince valve? Or...is it actually returning the tractor back to the state it would be if the valve were not installed...meaning no excess flow to the tank through the prince valve, but full flow available to the lift, which happens to be blocked by some unknown operational circumstance (something you are doing with the lift.) It might be true that the lift system has it's own relief, and therefore could never be blocked.. This would make the statement irrelevant so not worth worrying about.

I think the size of the valve is reasonable and also I see no apparent reason to use a pressure relief on that valve because it will send excess flow to tank.

 

[Harvest Moon]

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

I like the sounds of this, if I'm following it right.

Seems like the Surplus center valve at 8 GPM is a better match and basically it would be used to block/divide the flow at a variable but selectable rate and dump any excess flow back into the return??

And there is little need extra pressure relief?

And this will allow us, at the flip of a lever to set our tractors to their original 3 pt performance or choose an infinite range of flow rates to find the best rate for a variety of situations??

Sounds great! Why didn't Kubota think of this?

 

[Harvest Moon]

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

But, is it still just a guess that changing the flow rate to the PCV will solve the problem?? And if it is a fixed rate pump, does it mean anything that the PCV seems to function the same at different RPMs like teg pointed out?

I'm guessing the proof is in ht1's post, has anyone else tried this:

i can get smooth lift if i lift my loader at the same time i lift my 3 point this is not practical but you can see how the 3 point should work.

 

[Harvest Moon]

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

I bet if someone were to mechanically tie the lever on one of those valves to the feed back linkage they could make the original inching valve feather smooth.

 

[canoetrpr]

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

EE_bota:

Much appreciate your thoughts again.

At Princess Auto, I first gravitated towards a very simple flow control valve - variable orifice - like you have described. They had one for about 30 odd bucks. The concern there is that it would increase the pressure on the OUT port.

What you were recommending with installing a relief valve in series with the flow control valve is effectively what the flow control valve I have linked to gives you - except with the output pressure being regulated to the input pressure - which is all we need here since we are only interested in reducing the GPM and not interested in mucking with the PSI of the fluid.

The way I read the specs of the Prince valve, it is simply,not allowing an escape route for all the pressurized fluid to the excess flow port in the event that downstream the pressurized fluid is completely stopped. I *think* you could still turn the valve down all the way to zero and it would let the fluid escape through the excess port. I still have a question mark here much like you.

Harvest - you understand absolutely correctly. Once installed, this flow control valve will allow us to control the flow with infinite granularity between 0 and full flow (about 7 GPM) without any change to the pressure. So we could go to the original behaviour just by opening the valve all the way.