Question regarding positional control valves

[SylvainG]

At least, that's what my service manual calls it. I'm talking about the valve that controls the 3PH arms. On my tractor, it has 'infinite' position. Meaning, where ever I move the position control lever, the lift arms move accordingly and stay there. I'm trying to find on the Internet how this valve works but all I can find are videos of how directional control valve, which, from what I can see, is more like a standard FEL or backhoe valve. Anybody has a video showing how a positional control valve works? I'm curious.

Thanks

 

[ptsg]

Check some service manuals. Most will have a decent description how the position control valve works, with diagrams in different positions and color coded flows, as in pressure, tank, etc.

 

[BeezFun]

I have never seen a good youtube video or animation of the basic operation of the 3pt control system. When you move the 3pt lever, you are operating a pilot valve rather than a direct control valve like the one on your front loader. That's why you feel that lag before the 3pt arms start to move after you move the lever. The lift arms themselves have linkage connected to the control valve and tell it when the arm has reached the height that corresponds to the position of the 3pt lever. That shuts the control valve off and the 3pt arm stops moving. If you've ever seen a large tractor, the hydraulic cylinders for the 3pt arms are external so you can see them. That makes it a little more easy to understand than on small tractors which have a rockshaft and the lifting mechanism is internal so you can't see it.

If you have the service manual for your tractor, there is sometimes an overview at the beginning of the hydraulic section that describes in general terms how everything works. You might also learn something from the hydraulic circuit diagram.

 

[rScotty]

I don't know of any good videos of 3t control & hydraulic flow. But there is some good printed material. Most all 3pts work in the same or very similar manner. Here's one. Both Yanmar and JD have exceptional artists & ops manuals.
rScotty

View attachment YM240Hydraulic System Workshop manual.pdf

 

[SylvainG]

Thanks. my Kioti LK30 service manual do talk about the control valve, but just briefly. The hydraulic diagram wasn't much help since although the lever is shown, it doesn't mention how the positional is performed. Here's that part.

Thanks for the service manual, most I saw are for sale (including mine which I had to buy). I'll take a look.

 

[i7win7]

The 3pt feedback mechanism/cylinder/rock shaft is inside the tractor. This video of the insides of old ford tractor may be instructional
Jubilee/NAA three point lift adjustments - YouTube

 

[SylvainG]

Thanks, I did notice though when he raised the implement, the speed was fluid. When I raise my 500 lb snowblower on my LK30 3PH that can lift 1750 lb at 24", it is really jerky. It raises fast and stop almost instantaneously when it reaches its set height. The whole blower shakes when I lift it. Is it normal? Couldn't find an adjustment to control the speed of raising (I know about the lowering speed adjustment knob).

Edit: Saw this, might be the same issue: https://www.tractorbynet.com/forums/kubota-owning-operating/221524-l-series-jerky-3ph-jeffs.html

2nd Edit: I've started another thread since this question does not directly relate to the control valve but the way it's implemented.