Raising the 3ph with ate of drop control / lockout closed

   / Raising the 3ph with ate of drop control / lockout closed #1  

joshuabardwell

Elite Member
Joined
May 6, 2012
Messages
2,728
Location
Knoxville, TN
Tractor
Bobcat CT225
The manual for my tractor says not to operate the 3ph position lever when the rate-of-drop valve is all the way closed, because it will put the system into relief and can overheat the hydraulic oil. Seems pretty straightforward. But in another thread on TBN, someone said that, on their tractor at least, the valve only applies when the 3ph is lowered, and raising the 3ph with the valve closed didn't matter.

I don't know much about plumbing on these tractors. Can anybody speak to this discrepancy? Is this just something that is different on different tractors, or am I misunderstanding something?
 
   / Raising the 3ph with ate of drop control / lockout closed #2  
Our 3 Kubotas as well as the Kubota and Deere that Dad used to have will all lift when the valve is closed, they just wont lower.

Aaron Z
 
   / Raising the 3ph with ate of drop control / lockout closed #3  
My JD950 owners manual said if was cold out and wanted to heat the oil up faster to do just as you said. My Kubotas manual doesn't say that at all. I did it on my JD a couple of times and the sound did change can't say if it helped or not. Oh I just remembered it did say do not close all the way,just turn it in.
 
   / Raising the 3ph with ate of drop control / lockout closed
  • Thread Starter
#4  
Our 3 Kubotas as well as the Kubota and Deere that Dad used to have will all lift when the valve is closed, they just wont lower.

Just to clarify, it will lift. If my understanding is correct, that's what's supposed to put the hydraulics into relief. Or something.
 
   / Raising the 3ph with ate of drop control / lockout closed #5  
3pt operation is one of those things that a tractor owner should know from day one.

Three functions, Raise, Neutral, Lower.

Raise: Pulling the lever up will cause the cyl to fill and the 3pt arms to raise until the cyl is full. If you keep applying lever to the 3pt, the relief will sound off and dump pump fluid to tank and the engine may labor. When the 3pt is where you want it, push the lever back to neutral.

Neutral: Locks the 3pt and if all things were perfect, the 3pt would stay in the position you left it in.

3pt Lower: Allows the fluid to exit the cyl and the 3pt arms will descend. Pulling the lever back to neutral will stop the descent.

Descent knob: Purpose is to set the descent rate slow/fast, whatever. The other purpose of the descent knob is for transport, and by turning the knob right or IN, the fluid is trapped in the cyl and the 3pt will stay is a set position.

You can still raise the 3 pt arms when the descent orifice is closed off by the descent knob.

There is a relief valve and a safety valve in most 3pt systems. The relief valve can be set equal or lower than the main relief valve.
 
   / Raising the 3ph with ate of drop control / lockout closed #6  
I accidently tried for about 5 minutes to raise the lift on my old grey market Yanmar 4220 with the decent knob closed accidently and it damaged something in the lift. From then on it would jump up and down constantly with the lift raised. It would leak down a bit then the hydraulics would pump back up. I think it was a seal leaking.
EDIT: it wouldn't raise or lower with the decent valve closed
 
   / Raising the 3ph with ate of drop control / lockout closed
  • Thread Starter
#7  
3pt operation is one of those things that a tractor owner should know from day one.

Three functions, Raise, Neutral, Lower.

It sounds like you have a Kubota with quarter inching three point. The Bobcats have position control. Once the three point is up, there's no way to continue to try to raise it.
 
Last edited:
   / Raising the 3ph with ate of drop control / lockout closed
  • Thread Starter
#8  
EDIT: it wouldn't raise or lower with the decent valve closed

I guess they don't all work the same after all. Mine definitely goes up with the valve closed.
 
   / Raising the 3ph with ate of drop control / lockout closed #9  
The only real way to know what is going on with your 3PH system is to have a hydraulic flow diagram. There are certainly various ways of implementing flow and control for various brands/models. In the diagram below of my New Holland TC45D, the hydraulic fluid flows from the HPL control valve (#11) and into the flow control valve (#12). The flow control valve is a drop control needle valve, a ball check valve, and an emergency pressure relief valve if there is a sudden down pressure applied to the 3PH like something dropping onto a raised implement causing the lift cylinder to see excessive pressure above 3500 psi. The normal system pressure maximum on my system is 2500 psi.

By following the flow arrows, you can see that fluid will flow in two directions in the HPL valve. The direction depends on whether you are raising or lowering the lift arms. When the arms are raised, the fluid bypasses the needle valve and goes to the ball check valve. The ball lifts and allows fluid into the cylinder (#13) to lift the arms. When fluid stops flowing, the backpressure closes the ball check valve and pressure is applied to the needle valve and the emergency relief valve at the same time. If the HPL valve is moved to lower the arms, fluid flows through the needle valve opening. If the needle valve is completely closed, no fluid will flow because all three valves are closed, trapping fluid inside the lift cylinder. If the needle is open, fluid exits the cylinder at a rate set by the needle to allow a controlled dropping of the implement.

With a flow diagram such as this, you can fully evaluate what occurs inside your system. Without a diagram it's just a battle of SWAGs and opinions.;)

HydSys-TC45.jpg
 
   / Raising the 3ph with ate of drop control / lockout closed
  • Thread Starter
#10  
Where can I get the flow diagram? Dealer?
 

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