I have a Daewoo solar lc-3 excavator which stalls the engine when any function is used if the operator does not 'feather' the controls or if a cylinder is held at the end of its stroke.
Pump pressures are 298bar on both and the fuel pump and injectors have been overhauled recently.Does anyone have any ideas?

Did your hydraulic functions stall the engine before your injector pump rebuild? If no then it is something with your fuel system.
If yes, has anyone ever tampered with the setting on the pump controllers?
You could gamble and phone a hydraulic shop to come and set your pumps up, if your sure it's not a fuel system problem, but most shops don't know how. Your best bet is to unfortunately have the dealer come out and set the pumps up, and even most dealers don't know how, but they seem to muttle through it.
There are serveral adjustments that need to ne made, min displacement, max displacement, 1st stage curve, second stage curve and some have a swing setting to make as well. There is often a proportional pressure reducing valve on the controller that is controlled with Pulse Width Modulation, making it harder for the average guy to troubleshoot.

Hi Doug,
Thanks for the response. Yes the stalling problem was evident before the fuel system was overhauled as the owner thought that was the problem.I guess that some adjusting screws may have been tampered with by the owner in a misguided attempt to improve the performance.Iam lead to believe that the problem appeared quickly which points to something breaking or sticking,although it is much worse when the machine is hot.Unfortunately the dealership here on the east coast of Australia has just changed and the new people do not have the experience on the older models,and the old dealers dont want to know about it.

Have a look in the fuel lines there are a few banjo bolt fittings with screens in them in those little diggers and can get blocked not too sure in your model though

Thanks Newmanite. I believe that all the fuel lines were checked and the fuel pressure also checked out within specs,but I guess I should go through them myself to be sure as this was 2nd hand info.

It is an overload, i guess, and if you can post a hydraulic circuit and drawing, some people might be able to guide you how to do it...

I dont know how many pumps are ther in an excavator, hut I have seen two piston pump rotating block in one case/housing.

I am not sure also if the motors are driven by a separate pump in close loop, then the cylinders are driven by a separate pump in open loop.

Is there a solenoid on the pumps? You know what, the best way for the people to help is not just giving the model of an equipment. If there is a hydarulic system problem, a person familiar with the model or brand can troubleshoot it easily. But give a good hydraulic person an idea what is being driven by hydraulic system and he can imagine how to solve it. It could be imagined that an excavator has motor for slewing and maybe motors for forward/reverse drive. The forward and reverse drive of a crawl type can either be driven by a separate close system and the rest(boom, bucket, slew, etc) can be driven separate with another pump in open loop. How could people know by just looking at your daewoo solar lc-3?

Your problem is an overload, try to get a circuit and pump rating/control/circuit.

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If there is a hydarulic system problem, a person familiar with the model or brand can troubleshoot it easily

Most dealerships will have a hard time setting the volume stops and pressures on that pump. I'm 90 percent sure it's a kawasaki K3V pump, if not it will be similar in arrangement. You need to know pressure vs flow at two specific points for the horse power limiter: The first stage shift point and the second stage shift point, you also need two pressure vs flow points in between thos first two points The settings depend on whether one pump is under load or both pumps. You need to know the minimum flow rate setting as well as the maximum flow rate.
Having the above information is critical, and not common to find. Service manuals don't usually list them, as they want you to just buy a new pump. You could try contacting a company like 'Hydraulic Repair and Design', or 'Pheonix Hydraulics' or 'Quest Hydraulics' and ask them if they have any test specs for your machine or model number.
It's not easy to set these pumps up when you don't have the specs.

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The forward and reverse drive of a crawl type can either be driven by a separate close system and the rest(boom, bucket, slew, etc) can be driven separate with another pump in open loop

All current excavators of this class use open loops pump, at least for the last 15 years anyway. One pump will run the left track, swing motor and boom function, the other pump will run the right track and two other boom functions plus an aux. function. The control valve usually has an 'equal travel' valve that shares oil from the two pumps between the two propel motors.
In the old days you would often say a seperate swing pump which was a closed loop system.

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Is there a solenoid on the pumps?

It is quite common for ther to be a propotional prssure reducing valve on the pump controller that will respond to either: a signal depending on 'work mode' or it may come from the controller in response to a drop in engine rpm, (or load).

Maglub: I hope you will repost your earlier posting, did you copy it before you deleted it? This is all I have:

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Oh, so it is an open loop system. I'm still at work but here is a simple though about Constant HP control(CHPC).
CHPC valve is connected into the load sensing line (will recheck when I get home) wherin I could say that the possible minimum constant HP in the pump curve will be a stall pressure setting. Since the chpc valve is mechanically regulated by the swashplate...(more)

The pump doesn't have a stall setting, or maximum pressure. The pump does not destroke to zero, it has a minimum displacement stop, which on that machine will be somewhere around 9 gpm at high idle. The pump will continue pressuring up until the relif on the control valve pops open.

These pumps are kind of the opposite of load sensing pumps, in that instead of a load sense line they have a negative control pressure line.

If you vent the load sense port on a load sense pump, the pump will destroke at the stand by pressure setting, if you vent the negative control pressure port on the pump, it will move to full stroke.

If I get time i'll try and find a schematic of a kawasaki controller. I posted a schematic of a hitachi controller on a different thread a while ago, it is closer to load sensing than the kawasaki.

Here is a note on horse power limiters: They are really torque limiters, the only thing that makes the controller a horse power limiter is if the input shaft speed is held constant, which in an engine driven application is not so. If the torque is limited, but shaft speed increases, horse power increases and is not limited.
With that being said, in excavator world, we still refer to them as horsepower limiters.

I guess K3V is a bent axis piston pump... Does it look like or similar design with A6V?

I think if there is only one adjustment screw in the pump cover in each pump, that would be the HP regulation adjustment. If there are two more adjustment screw opposite to each other, those could be the min/max displacement(mechanical) adjustment screws.

The possible engine stall could occur at very high pressure setting of the beginning of regulation adjustment screw. If he can just back it off to a desired pressure(around 50 bars or below 100 bars for the meantime), the engine might not stall. This pressure setting can be monitored from the positioning piston measuring port/plug. If he can locate this positioning piston port, he can put a gauge there and monitor the pressure while tweaking the regulation screw with respect to main relief valve(if RV size is big enough to accomodate the full flow at operating pressure) setting. If the relief valve is sized based on the minimum displacement(small), the minimum adjustment screw should be back off so that this relief valve could handle the minimum flow at highest pressure.

If you can set the beginning of power regulation and the minimum pump flow, I guess your engine will not stall...

I suggest that before adjusting the min and regulation I rather screw in the max mechanical displacement limiter to almost between half to 3/4 displacement.

This is still a guess since I really dont know the exact pump construction...

Doug, if the minimum flow is 9 GPM, the relief valve should be vent at idle, isnt it? Too much flow. Man, I dont like this type of system. Yep, I deleted it because its obstructing the thread and it was a little bit wrong too(A10VSO style).

I just read the A6V style, though I dont have the catalog which is more important to see some other performance data. I was thinking that the minimum flow could be somewhere around 1 gpm.

This message has been edited. Last edited by: maglub,

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I guess K3V is a bent axis piston pump

It's a swash plate design. The control piston runs parallel with the axis of the shaft. The displacement limiters are in the front flange and center block for the front pump, and in the center block and the rear cover for the rear pump. The pressure adjustements are on the controller which bolts to the side of the housing. One on the front pump, one on the rear pump. Attached are a couple of drawings of the controller, I'll try and get a schematic done when I get time. You can see there is a bit more to these controllers than standard ls compensators.

and..

Here is a schematic of the K3V tandem pump controller arrangement. Pretty complicated isn't it? It's all the mechanical feed back connections and 'net force' pistons that make it look that way.

This message has been edited. Last edited by: Doug Hanson,

K3V_Controller.pdf (89 KB, 35 downloads)

Yes Doug, humn quite complicated but not too much, although its going to crack my head to fully understand it without examining the control block/parts physically or maybe a pump manufacturers cutaway drawing...

Anyhow, the part that confuses me is the middle line to the middle annular area which acts like limiter to the travel of the opposite side. Meaning if the first pump flow is encountering resistance before the load(load pressure at the same time, if there is), that differential area piston will mechanically move the control spool(to the right) modulating the pressure to the positioning(postioning area> sensing area) piston(through proportional spool), and the swash moves to lower the flow until it balanced again. In this process, the middle annular area/volume becomes bigger and giving room for the other pumps control middle annular area/piston to move to the right modulating the pressure on the other pumps positioning piston. What confuses me is the cavitation that may occur if the opposite differential piston wont react(it should react to maintain HP control).

Another thing is the adjustable sprig force(#925) is not indicated which I could assume to be the one with 3 areas. I call it the beginning of regulation HP control adjustment.

I could say that the proportional reducing valve is just use to modulate any actuator speed using both pumps displacement. The potentiometer could be in the engine accelerator...i am not sure...

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Originally posted by maglub:
Yes Doug, humn quite complicated but not too much, although its going to crack my head to fully understand it without examining the control block/parts physically or maybe a pump manufacturers cutaway drawing...

Anyhow, the part that confuses me is the middle line to the middle annular area which acts like limiter to the travel of the opposite side. Meaning if the first pump flow is encountering resistance before the load(load pressure at the same time, if there is), that differential area piston will mechanically move the control spool(to the right) modulating the pressure to the positioning(postioning area> sensing area) piston(through proportional spool), and the swash moves to lower the flow until it balanced again. In this process, the middle annular area/volume becomes bigger and giving room for the other pumps control middle annular area/piston to move to the right modulating the pressure on the other pumps positioning piston. What confuses me is the cavitation that may occur if the opposite differential piston wont react(it should react to maintain HP control).

Another thing is the adjustable sprig force(#925) is not indicated which I could assume to be the one with 3 areas. I call it the beginning of regulation HP control adjustment.

I could say that the proportional reducing valve is just use to modulate any actuator speed using both pumps displacement. The potentiometer could be in the engine accelerator...i am not sure...

I'll have to fix that up, the middle lines are supposed to be cross sensing.

The proportional reducing valve adjusts the work mode of the pump. More pressure from the reducing valve results in a 'lower begin of destroke' setting.

It's usually PWM and gets it's signal from the machines electronic controller.


925 and 628 are the first and second stage HP limiting adjustments.

OK, it's fixed now.

K3V_Controller.pdf (89 KB, 25 downloads)