L**40 rear hydaulic pressure

4shorts · Dec 26, 2011

Guys I just scanned 13 pages from the hydraulic section of the Kubota 5740 service manual. If you think this may help you out I'll start the upload.

J_J · Dec 26, 2011

oldnslo; said:
JJ
my concern is that he does not have PB connected properly. Everything he is describing sounds like a series circuit where the tank port of the first valve feeds pressure to the next. By having the valves connected like this he would have flow to all functions all the time. That is what I asked him to check to see if the FEL system pressure followed his rear remote pressure.

Like spyderlk an you have both stated, there should be NO flow to the rear remotes when he is using the FEL.

He has not said where the FEL valve OUT flow is going.

He has not said where the PB from the remotes is going.

What would happen if he is using the PB port with out the PB sleeve or the hex screw insert.

Is the FEL OUT port plugged?

Kuboman, please answer all the questions we are asking, as it is imperative that we know all the details.

This is a mystery, but I bet it has a logical answer.

J_J · Dec 26, 2011

4shorts said:
Guys I just scanned 13 pages from the hydraulic section of the Kubota 5740 service manual. If you think this may help you out I'll start the upload.

Thanks, please do.

Now, if he only has the valve installed correctly.

kuboman · Dec 26, 2011

I did check one on the dealers lot and yes it was 2500# at the rear. I did not check the loader so I do not know what the relief was set at. I do know most these tractors come with the pressure set about 800 psi low. I will go back and check both the loader and rear remote again.
I did not have any remotes on mine and I installed one/ the first.
I do not have the pressure gauge teed. I unplug a loader port and use it to check the pressure. Same with the rear remote. I plug in the gauge and bypass to get the pressure.

kuboman · Dec 26, 2011

4shorts said:
Guys I just scanned 13 pages from the hydraulic section of the Kubota 5740 service manual. If you think this may help you out I'll start the upload.

That would be great, I don't have a scanner otherwise I would have done that too.

Everyone can have a read and maybe I have miss interpreted or something. Hope so cause this all makes no sense.:thumbsup:

J_J · Dec 26, 2011

The only logical explanation I can come up with now, is that the pump is capable of 3200 psi, and the pump flow is gong to the remote first, and the remote valve is set to 3200 psi. After that it goes to FEL valve.

kuboman · Dec 26, 2011

J_J said:
The only logical explanation I can come up with now, is that the pump is capable of 3200 psi, and the pump flow is gong to the remote first, and the remote valve is set to 3200 psi. After that it goes to FEL valve.

The pump I am sure is capable of way more than 3200psi. That is why there is a relief but there is no way that is evident that it can get higher pressure to the remote.

4shorts · Dec 26, 2011

J_J · Dec 26, 2011

After reading the downloads. the only high pressure I can see around 3200 psi is the safety valve, and this is set high at the factory.

In order to read the safety pressure you would have to have an external pressure supply for testing, or you would have to have a sufficient load on the cyl up to the relief pressure, and a gage in the test port. .

I believe the reason for the safety valve, is once the 3pt is in neutral, the 3pt cyl is closed off and should an unexpected load appear at the 3pt, the only relief for the 3pt would be the safety.

For instance, you are removing a load from a trailer, and when you move the load off the trailer, and if it is to much for the tractor hyd, either the tractor front end will raise up really quick, or the safety relief will blow and the load will settle down to the ground.

Pump flow goes to the FEL, and the PB out from the FEL, feeds the rear hyd block, and I am assuming that you used the PB out of the hyd block to feed the remote valve. What kind of remote valve did you use, and where did you run the PB if the valve had PB, and where did you run the OUT/return from the remote?

There is no explanation for the 3200 psi reading observed on a gage plugged in at the rear.

Chilly807 · Dec 26, 2011

This is really getting strange... according to the scans, the oil flows from the pump to the FEL valve, where it is subject to pressure regulation by the PRV valve built-in-to the FEL control, both when applied to the FEL valve spools, and ALSO as it flows to the PB sleeve.

This alone means there should be no pressure anywhere in the system higher than the setting of the FEL PRV, which we think is set correctly at 2550 psi.

From the FEL valve PB port (sleeve), oil goes to the distribution block where it is routed to both the 3 point valve and the adapter for the external hydraulics, if fitted. I don't really understand how the block acts as a series circuit for the hyd outlets and the 3 point, but I can guess that function is performed internally.

The scans are a little bit confusing, because they are also written from the standpoint that the tractor may possibly NOT have an FEL valve or loader. That's why the hydraulic block has a "pump" connection identified, when in this case that is actually the PB line from the loader valve.

My question is, how is the working pressure regulated on a tractor that doesn't have an FEL or a control valve for one fitted ? The lower picture in scan 15 shows a relief valve, which I think is the main relief valve for the tractor, since the FEL relief valve is normally an internal item in that valve itself. I think JJ is right about the safety valve, it's designed to protect the tractor from an induced load on the 3 point hitch.

This still doesn't explain how you can have 3200 psi at the rear remotes, unless I don't understand how the PB pressure is not regulated by the PRV in the loader valve.

All I can think of is something is either defective or connected wrong.

Sean