Kubota L3400 - 3PH Action @ 2000 RPM





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Published on Oct 2, 2011

This video shows the improved 3PH action after cheap mods. Tractor is running @ 2000 RPM. Click "show more" for more details v.

Thread here: http://www.tractorbynet.com/forums/ku...

Acceptably smooth action, with control granularity of about 1/4". I will post additional videos in the future to show how finely i can bump up the 3PH.


Bought a used L3400. The 3PH was so jerky and violent, the tractor was pretty much unusable. Did a bit of experimenting and came to 2 conclusions.
1. Hydraulic flow rate to the cylinder is too high for the system design.
2. The control valve is not adequately damped, doesn't respond proportionally and requires too much of a delta (set point to feedback) to respond. This caused the hitch to jump an inch at a time, with a violently angry abrupt jump.

Position Control Valve is the part # YR909-00100 which is one of the more notoriously bad ones.

What it used to look like:
(other people's links - but mine was at least as bad, maybe worse)

What I did:

1. Reduced the flow to 3PH position control valve by diverting some of the flow after the FEL back to tank. Used a pressure compensated flow controller.

I plumbed this flow controller in to be fed from the power beyond port of the FEL contol valve and its outlet supplying to the 3PH, while the excess flow goes back to tank. The nice thing is that the valve is flow adjustable (hence 3PH cylinder rate) and is pressure compensated (3PH lift capacity is not reduced). Note that this valve has absolutely no effect on FEL operation, capacity or speed.

2. I disassembled the position control valve and chamfered the control edges of the main spool by 200um. These small chamfers reduce the "dead zone" of the control valve and make the valve far more responsive to small lever changes. In short, the lever doesn't need to be moved such that the hitch jumps 1" at a time to catch up to the difference. In the active region, the hitch now jumps ~1/4" (at most) at the time. Also, a chamfered flow in on the spool smooths out the initial flow of a given motion.

The tradeoff:

Max Lift speed is traded for smoothness of operation. However, what I like about this solution is that the pressure compensated flow control is fully adjustable. I can change the setting on the fly depending on the work I am doing. If I bump up the flow, it will get faster, but it will also start to look jerkier.


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