L**40 rear hydaulic pressure

[kuboman]

This is what I was thinking at first, too. But if that were the case, unless the FEL relief is isolated from the rest of the system as soon as the pressure rose above 2550 it would open and limit pressure throughout the system, all the way back to the pump outlet.

I think the key to this is where the FEL relief is sensing the pressure. If the most you can get at the FEL ports is 2550, it's internal to that valve and disregards everything else. The main safety valve, set for 3200 psi, is what's limiting the rest of the system here.

OK, let's consider for a moment what is protected, and what isn't. The FEL is fine, it's limited to 2550. Assuming the 3 point is capable of containing 3200 psi, it's fine. The only problem, at least so far, is the pressure out of the rear remotes, which is also at 3200 psi.

Maybe we should be looking at the new rear remote valve, and whether or not it has an internal relief. If it does, and I suspect that IS the case, it's just not set correctly. That's why Paul's tractor, and junkyarddog's too, are both at 2300-2500 psi, either because they were adjusted correctly at the factory, or they may have a different remote directional valve.

As I understand it, kuboman bought the kit from a Kubota dealer, which consisted of hard lines, a set of quick disconnects, the adapter plate, AND a valve assembly with directional control lever. I think there should be a relief valve built into that valve body, to limit the pressure output at the remotes. I guess it's possible that there are a couple different options available when you order the remote kit, and one of them doesn't have an internal relief.

I don't really understand the logic behind this set up. Why would Kubota build a tractor without a main relief valve? They are assuming that any add-ons will have their own internal or external reliefs, because obviously in this case the FEL valve is not controlling the pressure downstream in the system. It must have something to do with where that relief valve is taking it's pilot(sensing) pressure from, as we're starting to see.

Sean

The RR does not have a relief. The main relief does the whole system because it must go through it. It is a series system.

 

[kuboman]

Well boys forget everything I said!!!!! I had my L4240 in the shop and ran some test. This is what I came up with.
Note that all the test were done at the rear remote in the up and down ports. Also the 3pt would not go up with any other valve in use.
1st was to test the psi at RM with boom on the floor, it was 2700psi. When I went up with the boom psi went over 3000psi.
2nd Boom off the floor psi was 2700 but with rm in use, boom would not come down but the psi stayed at 2700.
3rd Boom off the floor psi at 2700 the bucket would go up psi would go up maybe 50psi. When bucket was going down psi would stay the same. It was working the way it should.
The 3000+psi only showed with the boom in the going up mode. One thing that I couldn"t understand, if the boom well go up why well it not come down?
I have looked at the drawings of the loader valve all morning and can't see anything why this should happen. Makes me think, are the drawings and schematics right iin the manual. How could one find out if there is a update for the manual.

Have you checked the relief pressure at the loader and rear remote? This is where I get the discrepancy.

 

[Leejohn]

I didn't do it today because my other gauge has lost the oil out of it. When I checked it before it was at the 2700psi. I don't remember if I checked the boom or the bucket system when I done it.
But anyway you look at it I'm picking up the 3000+psi at the rear remote just as you did. It shouldn't be unless some pump psi is bypassing the relief valve somehow and the drawings do not show that.

 

[dfkrug]

This is what I was thinking at first, too. But if that were the case, unless the FEL relief is isolated from the rest of the system as soon as the pressure rose above 2550 it would open and limit pressure throughout the system, all the way back to the pump outlet.

You're too fast, Sean. I deleted that part of my last post, but not before
you saw it. It does not matter if you have two RVs, or which order
the valves are in. For an open center system, the RV set the lowest will
determine the system relief. Kubo's Kubota has something unusual in
the plumbing and I sure would like to know what it is.

I was also surprised to find my Kioti with factory FEL and AUX has only one
RV like the Kubota. (I am not including the 3950psi shock-RV in the
3-pt.) You only need one, but when you add aftermarket valves, you
often end up with more.

 

[J_J]

The safety relief is not there to regulate pressure. It is there to prevent blowing out the casing, seals or piston. The 3pt cyl is essentially blocked off when the 3pt lever is in neutral, and if the 3pt suddenly experienced an extra heavy load, the safety relief would relieve the excess pressure. The basic tractor usually only has a relief for the 3pt, and a safety relief.

I believe the manual even shows how to test the safety relief, and that is by using an external pressure supply, meaning that the pump would not be capable of popping the safety relief.

I am thinking hypothetically that the relief in the FEL valve is a pilot operated relief, and only works when the FEL is being used, and providing the pilot. Other wise, it is not in the circuit.

If he only operates the 3pt and it reads 2550 psi, that will disprove my hypothetical unless there is a hidden relief in the 3pt circuit.

Still have not found max pump pressure.

Like the rest of you, I am perplexed by the operation of this hyd circuit, and the results of the test that have been done.

It will probably fix itself and leave everyone scratching their heads and wondering how in the he** did that happen.

 

[Chilly807]

You're too fast, Sean. I deleted that part of my last post, but not before
you saw it. It does not matter if you have two RVs, or which order
the valves are in. For an open center system, the RV set the lowest will
determine the system relief. Kubo's Kubota has something unusual in
the plumbing and I sure would like to know what it is.

I was also surprised to find my Kioti with factory FEL and AUX has only one
RV like the Kubota. (I am not including the 3950psi shock-RV in the
3-pt.) You only need one, but when you add aftermarket valves, you
often end up with more.

I'm getting curious myself now. When I added the rear remote to mine, the valve I used has a factory-adjusted relief setting of 2000 psi. My FEL valve is set for 2250 psi, and I think the main relief is set for ~2300 psi. I'm going to check mine tonight, or as soon as I get a chance to pick up a spare male QC to attach to my test gauge.

I'll be interested to see if the pressure in the rest of the system is now limited to 2000 psi, and is being regulated by the relief in the rear remote valve.

Sean

 

[kuboman]

I am thinking hypothetically that the relief in the FEL valve is a pilot operated relief, and only works when the FEL is being used, and providing the pilot. Other wise, it is not in the circuit.

The problem with that theory is that the pressure at the RR maintains a very constant 32-3300 psi no matter what rpm the engine is. If it was not relieved it would continue to climb with engine rpm until something popped somewhere.

 

[Chilly807]

I am thinking hypothetically that the relief in the FEL valve is a pilot operated relief, and only works when the FEL is being used, and providing the pilot. Other wise, it is not in the circuit.

The problem with that theory is that the pressure at the RR maintains a very constant 32-3300 psi no matter what rpm the engine is. If it was not relieved it would continue to climb with engine rpm until something popped somewhere.

The flow diagram of the loader valve (scan 11 from Paul) shows the relief valve pilot source as being internal to the loader valve (inside the "box" diagram) and at the entrance to the relief valve. This means that it should control any over pressure in the whole hydraulic system, provided that the tank connections are of a large enough size to accomodate the full flow that the pump is capable of delivering without further increasing the system pressure.

If there is any restriction that prevents the full flow from going to tank, the whole system should be over pressurized, not just the rear remote. That's the part I don't understand. You had said that the loader never goes over 2550, even when dead-headed.

I think the 3200-3300 psi is the safety valve opening. You should be able to hear a slight difference in the sound of the hydraulics when the safety valve opens at 3200, as opposed to the loader relief opening at 2550.

Sean

 

[kuboman]

The flow diagram of the loader valve (scan 11 from Paul) shows the relief valve pilot source as being internal to the loader valve (inside the "box" diagram) and at the entrance to the relief valve. This means that it should control any over pressure in the whole hydraulic system, provided that the tank connections are of a large enough size to accomodate the full flow that the pump is capable of delivering without further increasing the system pressure.

If there is any restriction that prevents the full flow from going to tank, the whole system should be over pressurized, not just the rear remote. That's the part I don't understand. You had said that the loader never goes over 2550, even when dead-headed.

I think the 3200-3300 psi is the safety valve opening. You should be able to hear a slight difference in the sound of the hydraulics when the safety valve opens at 3200, as opposed to the loader relief opening at 2550.

Sean

I did mess with the safety valve and had the pressure reduced but it made no difference to the pressure at the rear remote. The safety valve is a closed system anyway and has nothing to do with pressures in the rest of the system.

 

[Leejohn]

I made this statement (Also the 3pt would not go up with any other valve in use) in my other post and it is not true... I was looking at the valve drawing for the boom and the work ports returning oil is feeding the PB port. I tried it and this true. When working the bucket the 3pt does not work. The work ports return oil goes to tank. Sorry about that, but I think you guys had seen that way before me.