Hi everyone Its my first post. I have been working as an independent mechanic and worked on mainly excavators for years. Poclain, Caterpillar, Komatsu, Volvo etc. I have one issue which i have been unable to diagnose. Its in pc220-7 excavator hydraulic valve bank as i am satisfied with the main pump. There is no issue in the pump as it has been exchange and rebuilt several times. In komatsu valve bank, there is flow merge/divide valve which seperates both pumps on some operations. So if i seperate the flow to check the performance of the pump, front pump unload pressure drops. While rear pump pressure remains in the range. ie 40 bars. The problem with this issue is that after half an hour of work excavator power drops and unable to move one track and stick also becomes slow.
What are you doing to split out the pumps? As I recall the pumps split out when traveling and operating another function. As I understand what you are saying is that after a half an hour of operation only one track loses flow and the stick only moves slowly? Does the stick still operate slow if the track is not being operated? What are your pump pressures when all this happens. Also why are you worried about unload pressure. It has no bearing on the operation of the machine. It sounds like you either have a pump problem or a load sense issue.
Thanks for your concern. This is my 4th or 5th case which i am unable to solve. Spliting of the pump is my own diagnosing step. Else all the operating functions stays as according to the service manual Pressures and flows of both the pumps are in required range. Means the pc valve, ls valve, pilot valve, unload valve, line relief valve, both main relief valve, etc has been exchanged with the new ones. If i operate an excavator its in best shape unless it starts loosing its power after half an hour or in one case within 20 mins. I worked on that same excavator for 6 months and then i came to know that if i seperate the pump flows the only thing which is out of range is the unload pressure of the front pump. Although if operate even in seperate flows the pressure of each pump is normal. Even exacavator works fine. Yes its only for testing while in flow divide mode. What i think is that there might be an internal leak within the valve bank which gradually weakens the complete system. Here we have lot of breaker use and most of the time breakers are operated in other modes than B modes too. And the breaker gas charge is not considered to be check which works as a cusion or shock absorber in the hydraulic system. Because of this valve bank might get bursted inside. Also even if the breaker is not used or in bucket excavator loose power.
what are your pump pressures over relief. you have to check pumps when they are divided by stalling left and right tracks.