[kevlar]

On my 9680 ford new holland tractor, the third spool I was using for raising and lowering the drill was really slow, so I switched it to another one and put the wing lift on that spool thinking it would be good enough for that. It works ok when the oil is warm but this morning it wouldn't lift them at all. I tried adjusting the screw on the back of the block but it made no difference. I remembered that last year all the spools worked alot better when I had the second fan running, so I had the lever set to raise the wings and pushed the lever to raise the drill up and the wings lifted great! I know the spool needs rebuilding because it makes a screeching noise when I use it but why does it work better when there is more draw on the hydraulic system?:5:

 

[lanwickum]

There is a signal system on most load sensing piston pump hyd system. It has to do with sending signal pressure to the pump to stroke up and deliver more oil and more pressure as needed. I am guessing you are having a problem with this. If you find the one that works, that may be were the problem is. Guessing the check valve for this signal network is bad in the working valve as strange as that sounds.

 

[lanwickum]

Had to refresh my memory a bit on this system. It is also called a resolver network. Not all ag tractors use this system. I know deere used to use similar system in maybe 9400 type tractor SCV valves. Guessing a bit on were these types of valves were used by deere. Theirs just acted different than most when a problem did occur. Has to do with now the check valves, or discs that deere used worked. Anyway, not finding info on New Holland tractor hyd systems. Wish I could help you more. Have a neighbor fighting his Ford 4WD hyd system. Not finding info on ford 4wd tractors either. Anyone lead me to good system operation manual I can figure most things out. Even a good schematic that includes valve internals should do it.

 

[lanwickum]

Reread and to make a long story short. It must be sending the signal to the pump from the valve used to run the fan. Not getting that signal from the others. That signal pressure is what makes the pump stroke up to flow more oil and/or more pressure.

 

[offroadnt]

The signal being discussed here is called the load sense signal. All spools should send a load sense signal to the pump and the pump is supposed to maintain around three to six hundred pounds more pressure than the highest load requires. This is achieved through shuttle valves built into the remote sections. The remote spools that are not being used dump their load sense signal to tank and the shuttle valves prevent the load sense signals from the valves being used from being dumped through the unused valves. Something is preventing the remote that's not working sending a signal to the pump, maybe a small piece of debris? Have your valves been serviced lately? Maybe someone didn't install the shuttler ball or plate between sections?

 

[custom_farmer]

I have a couple of NH 8970's that will do similar to what you are describing on occasion. When it happens I know it's time to replace all the o-ring type gaskets between the spool blocks, and there is a bunch of em. I've had it explained to me that when the o rings split, it allows oil to bypass somewhere in the system. Something to do with there being 2 pumps in the system, a charge and a pressure? I think? When the oil bypasses, the signal doesn't get sent to the charge pump to spool up, and the pressure pump runs constantly. When mine have done it, I can flip the 3 point switch to get more oil flow, or pressure.
I've talked to other owners that complained their floor boards would get so hot, they couldn't keep their boots on all day, both owners changed the rings, and the problem went away.
NH, now has backup washers for the o rings when you change them, I haven't had a problem since they were installed.

 

[kevlar]

Thanks for all the help. Rainy here now so might be a good time to rebuild the hydraulics.

 

[offroadnt]

I have a couple of NH 8970's that will do similar to what you are describing on occasion. When it happens I know it's time to replace all the o-ring type gaskets between the spool blocks, and there is a bunch of em. I've had it explained to me that when the o rings split, it allows oil to bypass somewhere in the system. Something to do with there being 2 pumps in the system, a charge and a pressure? I think? When the oil bypasses, the signal doesn't get sent to the charge pump to spool up, and the pressure pump runs constantly.

The orings make sense but your a little mixed up with how the valves interact with the pump.

The charge pump is a fixed displacement pump that provides constant flow and pressure to the main hydraulic pump and usually some lubrication circuits, pressure is maintained usually around 200 to 300psi depending on OEM specs and is controlled by a relief valve. The charge pump produces more flow than the main pump and lub circuits will need.
The main pump is a variable displacement axial piston pump that is usually set to around 500 to 600psi over demand pressure and provides flow as required to maintain this pressure. The signal for pressure control is provided from the valve body to the valve on the pump which in turn sends oil to the swash plate piston within the pump, forcing it against a spring and thus causing the pump to begin stroking and providing flow.

Load sense hydraulics 101

 

[steelman]

load sense

That's a pretty good tutorial. Another point to remember is load sense control will almost always be in parallel with another pump control, in heavy industry pressure compensation is the most common. In the mobile world the equipment I'm familiar with will use a horsepower control in conjunction with load sense.
Load sense is nothing new, 1969 was when it was dreamed up if I remember correctly.

Steelman

 

[offroadnt]

Load sense is nothing new, 1969 was when it was dreamed up if I remember correctly.

Steelman

I'm thinking Case was the first to use load sense hydraulics on a mass scale when they introduced their 90 series tractors in the late 70s.

John Deere switched from pressure compensated to load sense around the mid 1990s?

 

[Diesel POWER]

The problem is the O-rings on your primary shuttle. you will need to take the valve off. If you look at the back side of the valve there will be a small screw slightly recessed and about 3/8inch in diameter. It will either be a hex (allan wrench) or a big slotted (flat crew driver). They will be Very tight and you may need an impact driver. Not air wrench! once you get it loose, un screw it and take it right out. you will see either no o-ring or a broken o-ring. it should have an o ring on it. And it usually is not the valve that is giving problems that has the blown ring. it is commonly the valve beside. best thing is to check them all while it is off.