Just read your posts about the problems your having with the Kobelco excavator. I've only worked on one Kobelco but just about all of the brands are similar in the way they work nowdays and I've had the displeasure of doing alot to both CAT's and Komatsu's. That said typically all newer excavators run at least two variable displacement piston pumps for hydraulic power. Whether the two pumps are in the same housing or in two different housings really doesn't matter, they all work basically the same way. They run two pumps so that there is always power available to a function even when another is being worked. For instance when digging and you are rolling the bucket your probably pulling the dipper to you at the same time. With one pump you wouldn't get consistancy either in speed or pressure between the functions but with one pump supplying the bucket curl and the other the dipper you have all of the pressure and flow available to make each function work properly. As to how they split the functions I guess that depends on the mfg. Typically though they tend to split the pumps when tramming with each pump supplying one track, but if you operate a function at the same time they it then ties both pumps together. They also tie them together when you boom up in order to give twice the flow to achieve greater speed coming out of the hole since your moving what are typically the two largest cylinders on the machine.
In your case you say some functions are effected but not others so it sounds like you've got one pump bad but then you also say it trams alright. Not having the proper guages it's really hard to troubleshoot hydraulics, especially on an excavator, but here are some things you can do. Try checking your tram with each track individually and see what happens. Often even with just one weak pump a machine will tram OK on the track hooked to the good pump, and usually with both tracks, this because the good pump has enough umph to do 90% of the pulling itself with one track. Either way the one tied to the "bad" pump will be weak as heck when forced to work alone. From there if one track does show up as weak then try tramming with the weak track again while booming up. Booming up should tie both pump outputs together so if the weak track 'gets stronger' with both pumps tied together then you know you've probably got a pump going out.
One thing you can't really go by is the sound of the engine. With the pumps being variable displacement as the pressure rises to it's max the computer monitors the engine speed and when it senses a slow down of the engine RPM's it destrokes the pump thereby decreasing the output GPM. For instance with lite load that needs say 2500 psi the pumps will put out 20 GPM but when heavily loaded and the pressire rises to 4500 the output will decrease to say 10 GPM. The computers main concern is to keep the PSI/GPM ratio within the optimum range based on the engines optimum HP/RPM range. If your problem was in the computer or one of the sensors feeding it then you'd more than likely see a problem with all functions and not just some of them.
Ok, that's about the only way to I know of an individual can even begin to check a machine without a manual, and a set of guages. Often you can go into the computer and check for any fault codes, and sometimes you can also pull up the system pressures, in a maintenance mode, using the systems own pressure sensors but without the manual to tell you how to get into that mode, etc then your pretty much stuck with the proceedure I just described.
I know it's not much to go on and even doing the checks like I describe won't give results that are 100% certain. However I can say that in just about every case I've seen of a pump going bad, barring the occasional catastrophic failure, I've seen the symptoms your describing with your machine and testing with guages has confirmed the symptoms were right on.
If you have any other questions feel free to ask and I'll do my best to answer. Like I said except for some minor differences just about all brands work in nearly the same way so I can probably get you at least in the ball park as to what to be looking for or at if you run into a problem. Good luck.
In your case you say some functions are effected but not others so it sounds like you've got one pump bad but then you also say it trams alright. Not having the proper guages it's really hard to troubleshoot hydraulics, especially on an excavator, but here are some things you can do. Try checking your tram with each track individually and see what happens. Often even with just one weak pump a machine will tram OK on the track hooked to the good pump, and usually with both tracks, this because the good pump has enough umph to do 90% of the pulling itself with one track. Either way the one tied to the "bad" pump will be weak as heck when forced to work alone. From there if one track does show up as weak then try tramming with the weak track again while booming up. Booming up should tie both pump outputs together so if the weak track 'gets stronger' with both pumps tied together then you know you've probably got a pump going out.
One thing you can't really go by is the sound of the engine. With the pumps being variable displacement as the pressure rises to it's max the computer monitors the engine speed and when it senses a slow down of the engine RPM's it destrokes the pump thereby decreasing the output GPM. For instance with lite load that needs say 2500 psi the pumps will put out 20 GPM but when heavily loaded and the pressire rises to 4500 the output will decrease to say 10 GPM. The computers main concern is to keep the PSI/GPM ratio within the optimum range based on the engines optimum HP/RPM range. If your problem was in the computer or one of the sensors feeding it then you'd more than likely see a problem with all functions and not just some of them.
Ok, that's about the only way to I know of an individual can even begin to check a machine without a manual, and a set of guages. Often you can go into the computer and check for any fault codes, and sometimes you can also pull up the system pressures, in a maintenance mode, using the systems own pressure sensors but without the manual to tell you how to get into that mode, etc then your pretty much stuck with the proceedure I just described.
I know it's not much to go on and even doing the checks like I describe won't give results that are 100% certain. However I can say that in just about every case I've seen of a pump going bad, barring the occasional catastrophic failure, I've seen the symptoms your describing with your machine and testing with guages has confirmed the symptoms were right on.
If you have any other questions feel free to ask and I'll do my best to answer. Like I said except for some minor differences just about all brands work in nearly the same way so I can probably get you at least in the ball park as to what to be looking for or at if you run into a problem. Good luck.
