3pt valve - how does it work?

[jbwilson]

I am just curious on how the 3pt hitch valve works. In particular how the positional control metres the correct volume of oil into the lifting cylinder.

I am trying to understand basic tractor hydraulics. Can anyone recommend a good source of information that I can buy that is relevant to my tractor. I am simply trying to fully understand how my tractor works - it's similiar to a Yanmar SC2400 with an Austalian version of a fel (self levelling due to Australian regulations).

Thank you.

 

[J_J]

Basically, in neutral, the 3pt valve directs the fluid through the valve to tank.

The raise mode opens an orifice that will let fluid flow to the 3pt cyl and the cyl will extend fully until the relief pressure is met.

Lower mode allows the fluid to flow out of the cyl through an adjustable orifice, through valve and to tank.

The adjustable knob under the seat will also lock the 3pt in any position for transport.

 

[jbwilson]

J.J

Thank you kindly. Yesterday I had my 1st service performed on-site by my tractor dealer who is located in Sydney about 300 klms away from Canberra. The service was done well, but because it is difficult to schedule services I will be doing the routine maintenance from now on. Good local tractor mechanics are hard to find and even my dealer is actively looking for a good local bloke. Anyway, knowing how things on my tractor work will be useful as future repair issues emerge.

 

[Redneck in training]

What JJ didn't tell you is that 3 point has positioning control. IN other words you select the position you want to maintain and the positioning will maintain it regardless of load and leakage as long as the engine is running. The positioning has a feedback to the valve and when the desired position is reached it moves the spool to neutral position and the movement of the cylinder stops.

 

[Tx Jim]

Redneck in training
You are correct that is "IF" position control is adjusted and operating as designed. When position sometimes called draft or load & depth control gets out of adjustment is what puts multiple gray hairs in the technicians head.

 

[LD1]

Yep, position control.

There are slight differences so I'll just hit basics, in my own words.

Basically there is a linkage between the 3PH raise/lower lever and the valve. This operates the valve.

There is also a linkage on the 3PH itself for the feedback. This shuts the valve off when the height you want is reached.

Best way I can describe it in lehmans terms is a lever like a wheelbarrow. With the raise/lower linkage connected to the handle, the feedback connected to the front tire, and the valve connected to the middle (load).

The valve "wants" to be in the neutral position. IE"wheelbarrow" flat. If you raise the 3PH lever (handles) you are no longer level. The valve "load" will raise (opens the valve). as the 3PH raises, the feedback linkage connected to the "front tire" raises. Once things are level again, the valve is off. And vice versa for lowering. The farther you raise the 3PH lever, the farther the 3PH has to raise to be in the "level" state.

I know its more complicated than that, this is just a basic idea to maybe help get a picture of whats going on.

 

[jbwilson]

Thank you to all. Looking harder at my set up, I recognised a rod connected to the rock shaft and the spool valve assembly for the 3 pt hitch. It seems to me that this rod connection operates the mechanism to switch the spool valve from oil flow under pressure to the cylinder to neutral mode when raising the hitch. The position of the 3pt lever establishes the position at which the switch is triggered. As the rockshaft rotates, the rod angle changes causing the switching mechanism to move to the point needed to trigger the valve into neutral position. When lowering the hitch, the valve opens up the oil flow from the cylinder to the oil tank, under gravity pressure. If the hitch is not at it's lowest setting, a new position is created for the switch for the valve from oil flow to neutral mode which is then triggered at a particular point by the dropping rockshaft.

I hope my understanding is correct. Again, thank you to all.

 

[MikeFarm]

Hi JB

Here is a link to a detailed but fairly clearly written Wikipedia article on the values and all the other stuff needed for a hydraulic system to work.
Hydraulic machinery - Wikipedia

I'm from Sydney and have a farm in the Central West, NSW.

cya
Mike

 

[jbwilson]

Mike - Thank you for that - added the link to my growing collection of hydraulic websites. I bought my little Yanmar EA2400 to landscape my 1/2 acre suburban block. When it's all finished the tractor will live an easy semi-retirement mowing the grass. Until then it will be lifting weights with its 4 in 1 bucket and carry all, cultivating the ground with its box scraper with 3 tines and tilling the ground with its 20 blade rotary tiller. I will still have to dig trenches by hand, as I ran out of space to store a back hoe. Its small stuff compared to the capabilities of your Kioti. My tractor weighs only 540kgs without the fel and attachments and is easily overpowered by its 24 hp diesel - great for running PTO equipment, but not so good with lifting really heavy weights and pushing dirt. Fel performance is significantly hindered by geometry of the self-levelling loader - a requirement of Australian regulations - although it would be less of an issue with larger tractors.

I find hydraulics interesting although I don't find it easy to understand and so well written articles on this subject are welcome. Reading TBN posts on hydraulics are also very useful - there are a few prolific contributors out there in TBN land.

By the way - have you compared Australian prices to US prices on tractor attachments and hydraulic components. It seems that we can pay up to 3 times or more than our US colleagues. That's a good reason to understand how the components on your tractor works so that when parts eventually wear out you can order components online.

 

[MikeFarm]

Hi JB

Have not compared US prices on components, I would not expect such a huge difference, perhaps 50% difference is understandable. Lets hope our tractors don't wear out soon Have fun with your Yanmar - they are nice tractors.

Mike