Fiat-Hitachi FB100 backhoe hydraulic problem (?)

Hello guys,
I´m writing from spain, my name is Tomás, and I found this excellent forum searching internet for help with the problem (if it really is one) of my backhoe. It´s a 1999 Fiat-Hitachi FB100 with about 10.000 working hours, and I think this is very similar to some New Holand and Case backhoe models.

This machine has a conventional hydraulic system with a tandem-gear pump, no load sensing, no servo-hydraulic, no fancy joysticks. The backhoe valve assembly is built up by 4 HUSCO-valve sections, in this order (from pressure inlet): Boom-swing-bucket-dipper, all of them equipped with relief valves, except the bucket and dipper rod-end sides. Between every two sections there is a spring-loaded check-valve. There is a inlet-end cover feeding pressure to the backhoe carriage clamp-mechanism. The outlet end cover incorporates a back pressure valve and regenerative check valve.

All hydraulic is working fine, and with speed varying with motor rpm. Steering, loader and stabilizer without any problem, and even the hoe while not combining cylinder movements with the boom cylinder. I try to explain: All three cylinders (boom, dipper and bucket) have a lot of power and work with more than enough speed. Also the combination of dipper and bucket cylinder is working fine and fast. But when I try do do a combined movement including the boom cylinder, I only can do this moving either the boom very slow (this means, not to move it´s control lever more than to half it´s way or even less) or, moving boom faster but of cost of dipper oder bucket cylinder speed. A combined movement of two or three of the sections can only be done very slowly, but this independent of motor rpm. If I rise rpm the problem still is the same, only at a little bit higher "total speed", but in my opinion very below for doing a serious, paid job in a given time.

I don´t remember if this was the same when I bought the machine 10 years ago, by this time I was a total backhoe-newbie and use the machine only for pleasure doing some work on my own property. I learned how to maintenance, repair and even improve this machine; I´m not afraid of doing difficult tasks when I know what I have to do.

All the three backhoe cylinders are in well condition, they hold their position even under load, so I think I can exclude internal cylinder leakages and I suppose that the "problem" also can not be produced by bad, worn or hanging vale spools, as every one of the sections work absolutely fine. I also think that the problem will not be caused by the relief valves, because of the good load-holding of every cylinder. And I can hear them well when they begin to work moving either cylinder to it´s end position (or "overloading" it). The only items I really don´t know if the can produce this problems are the check-valves between the sections, or the back pressure valve and regenerative check valve at the outlet.

And I don´t know if that what I´m experiencing is a absolutely "normal" physical princip, equilibrating the pressurized hydraulic fluid between forces to equilibrate them.

So, I hope that I have described the problem less or more understandable and I would greatly apreciate if somebody can give me any hints (or even if you all agree that what I´m observing ist "totally normal"). If you have questions or need more details of the internals of the valve body, don´t hesitate to ask me.

Best regards and thanks in advance for reading this long text.

Tomás

Hello,
I´m somewhat amazed that there is not even one answer, maybe it is my fault because I have not described the problem in an understandable manner? Or is it because I´m new in this forum an first have to participate before making any question? Don´t know!
Or is my problem so very specific that nobody has experienced something similar? I really would greatly apreciate any answer.

Sorry for my english, it is far away from "perfect"

Tomás

I think the problem is that it really wasn't a popular machine here, I'm not even sure it was marketed here long if at all...

I've never seen one but if it's like a Case, the old ones do slow down when you use multiple backhoe functions at the same time but I think that was some years prior to 1999. Maybe you've just become more proficient at operating it?

I am not familiar with this particular backhoe, but I know something about this type of hydraulic system. In order for the functions to move slowly there must be excess flow from the pump that is being driven over a relief valve. Based on your description it is most likely the main relief in the inlet manifold or the workport reliefs in the boom section. You would probably need to measure the stall pressure with a pressure gage to determine which one. It is possible for the setting on the relief valves to be low and still have good load holding ability. Particularly if the problem is with the main relief in the inlet.

Before you adjust anything it would be good to find some documentation that shows what the settings should be. It is possible that the settings of the reliefs are correct and the machine is operating as it should be like Grady suggested.

I do not think that the problem is related to the check valves between the sections. These are pump load checks that prevent oil from the cylinders flowing back into the pump passages when you have high load on the cylinders.

Thank you for your answers. I comment:

@Tags: Maybe this particular machinde/model was not very popular in US, but I think it is a very common machine, the manufacturer changed a few times it´s name, but the machine was the same: Fiat-Hitachi / Fiat-Kobelco / New Holland / Case-New Holland. It is very similar to a LB75 or LB90 model, and also practcically equal to a Case 580... don´t know the letter, but one dealer told me that since Case belongs to NH, the machine is the same.

@Grady: Sure, I´m a lot more proficient then when I bought this machine, I remember that one of my first "tasks" was to dig a hole to bury my mother-in-law´s (small) (and dead) dog; I needed about two hours and my clothes were wet of sweat But I think that is is not a "virtual problem" that has appeard with more skills, because the (with boom) combined movements are so very slow, that a serious, money-earning working would not be possible. For my own tasks it will work, but even by doing this every time I think: That can´t be serious!

@griffon02345: I have to confess that I never checked the hydraulic pressures, because as everything (without the mentiones combined movement) is working fine, I supposed that the pump pressures, flow rates and the relief valves are ok. When you speak of the "main relief valve in the inlet manifold", you refer to to hydraulic systems main relief vale? Because the backhoe valve-section doesn´t have a relief valve at the inlet.

For testing the workport relief-valves it is necessary a special tool I don´t have, but I think I can do a careful test dismounting the reliefs and substitute temporarilly with a "blind plug".

I have the repair manual for the "Fiat-Kobelco B95-B100-B110B-B200 4WS FB100.2-FB110.2-FB200.2 4WS" which fits for my machine, at least in everything I worked with, also I´m not sure if every detail is exactly the specified for my machine. In the "hydraulic section" I can find the pressure settings for every relief valve.

BTW: Is it recomended to work alwas with "relatively" high motor rpm? As speed for (nearly) everything is sufficient with about 1.300 rpm I didn´t see it necessary to go higher - but as I described in my first post, even at high rpm (2000+), the problem keeps to be the same, only with some higher total speed (but faster not according to the higher rpm).

Again, thank you a lot for your answers, I will give feedback when I found out something. In the meanwhile, if somebody has any more ideas, please don´t hesitate to post them.

Best regards, Tomás

Tomas,

I am surprised that there is not a relief valve in the inlet manifold. A gear pump hydraulic system must have some kind of pressure relief to give the oil somewhere to go when the cylinders are unable to move. You should be able to check the pressure settings of the reliefs by attaching a pressure gage that meausures pump discharge pressure. There may be a port for measuring near the pump or where the hose enters the valve. I don’t know specifically on this machine. You can stall each function (boom, dipper, bucket, etc.). The pressure will be limited by the lower of the workport relief or the main relief.

If you can accomplish your work at 1300 rpm then there is not problem with running at that speed. You will likely burn less fuel as well.

@griffon:

I suppose that I misunderstood you: Of course there are pressure relief valves, but not at the inlet manifold of the backhoe valve section. The system pressure relief valve is built in the loader valve assembly, and the rear pump relief valve is located in the stabiliser valve assembly.
And sure, I have to use the pressure gauges, there are three measure ports in te motor compartment, I got the manometers some years ago but still didn´t get the hoses (think, they are "Minimess"-Type).

Thank you again for your answer, I will report when I discover something new.

Tomás

But isn't his complaint that he can't accomplish his work? If my machine was working too slow and I was running at half throttle, I think I'd turn it up. Conclusions like this is why they pay me the big money. ; )

Hi @FB100-Backhoe

Did you get to the bottom of the problem?

what you are explaining is exactly the issue I have on my NH85, which is essentially the same machine.

If you are able to share what you found to be the issue would be a great help..

Many Thanks