Hello. We have a komatsu pc400-7 excavator. We are haveing problems with getting the merger valve to engage. We are having low lifting power in the boom and low steering power in the tracks. We have replaced the self pressure reducing valve do to high pilot pressure. That seemed to make all the functions a lot smoother. But lacking power in the boom and tracks. Really hoping someone could shed some light this and put us in the right direction. We appreciate any of all info. Thanks.
Have you checked for codes on the monitor panel yet? Do you know how to access the fault code and monitoring functions in the monitor?
Hi john. I have tried to google how to check for codes but haven’t had any luck. But I’ve gotten into the monitoring part of it and see that the merge function is turned on. But doesn’t seem to be working when demand calls for both sides of the pump. I don’t have any codes displayed on the home screen. We’ve checked all the spools and compensator spools pertaining to boom and track fuctions today but didn’t find anything that would raise concern.
Hi dude, Could you tell me whether your excavator is slow or weak? "SLOW" is a problem with low flow. "WEAK" is the unsatisfactory pressure. Then why are you thinking about "MERGE VALVE" ?? because of you checked and found that only one pump operating?? You have been thinking about "MERGE VALVE" then you 've replaced the "PRESSURE REDUCING VALVE" ?????!!!!!
Lachau brings up a great point. The merge valve only joins the pump flows when you are operating an implement while traveling. There is a spot in the monitor where you can watch the hydraulic pressures while operating the machine. To get into the diagnostic menu on a Dash 7 you press and hold the up button and then push 1 then 2 then 3 and let up on the up button. That should get you into the diagnostic menus. You can then use the up and down buttons to shift through each menu.
Hope to be helpful. Note that: Electrical merge solenoid valve ON ==> hydraulic merge valve disengage ==> Front pump and rear pump are separated. Electrical merge solenoid valve OFF ==> hydraulic merge valve engage ==> front pump & rear pump combined .
the machine was working fine. Then all of a sudden it seemed to start loading lifting power in the boom. To finish the job we would have to step on the travel pedals while lifting the boom with a load to get boom to raise, that would get to raise at normal speed. Then shortly after we started busting the main spool cap on the merger valve. So we started testing pressures and seen that our pilot pressure was 1500psi+ under load. So we were able to find out enough that sprv could be the culprit, we now have pilot pressure back down to 475psi, now we’re are Not busting spool caps anymore. Pump f and r are both at around 2700-2900psi. Not sure what pump pressure was before we started having issues. The machine will walk a straight line and seem ok, Just lacking power when turning tracks different directions, and lacking power when booming up with a load. Also machine works best in b” mode out of all the modes.
hey John I’ve been able to get to that point in the menu. But not sure where to pick up codes at or diagnostics. Thanks
Hi "4digger". Please see attached images.
Thanks for the info. Found a list of codes. D196ka Service return relay disc Dhpbma R pump p sensor abnormality F pump p sensor abnormality Dhs3ma Arm curl ppc sensor abnormality dhs4ma Bucket curl abnormality Dxa0ka Pc-epc sol disc there’s nothing much in the mechanical codes. Just some minor engine level codes. I would think all the pilot pressure problems should be fixed now the we have normal pilot pressure. Thanks in advance for the help.
I would check your pumps individually each one under a load, and see if your engine speed is the same for both pumps, when not, see if not, adjust your pc epc solenoid. You should should be at around 1790-1850 rpms
Hi jgm. I’ve had a gauge on both sides of the pump there both running between 2700-3000psi. Rpms are 1850-1900 rpms. Under a load it I think it went down to 1750 rpms. Thanks
How many hours do you have on the machine and the pumps. Pump pressures should be over 4,500 with a cylinder run to one end or another. The pressure sensors may not be reading properly so I would suggest installing a gauge capable of at least 6,000 PSI in each pump outlet to check the pressures. It is possible the pump is going bad and has spit out some debris that got into the pressure sensors at the valve but not real likely unless you find brass in the suction strainer or the return filters. The pilot pressure sensors are probably related to the pressure reducer for the pilot circuit that you replaced. It's probably time to start checking filters and the suction strainer in the hydraulic tank for debris. Did you get any change in pump and machine noise when the problem started. Does this machine use any other attachments like a compactor or breaker? I haven't worked on this particular model but I'm sure they have compensators that are hooked into the load sense circuits. If one of those leaks through you can get the same types of issues you are talking about.
All right, I recommend the following steps for checking: 1. Turn "EMERGENCY SWITCH" to "a" position. 2. Adjust PC valve.