We all know that CLSS system on komatsu macine is not a complicated system but sometimes we find some strange behavior on that system. In fact, I am doing the arm in relief and trying to raise the boom at the same time and I found that the pump pressure drop from 340 bar to 240bar when I use the boom raise and it goes to arm in relief when I stop the boom raise, Is that normal or there should be some leakage in the main control valve. I thought that the max load shoul be sent to the LS line.
Is there a shuttle vale that may not be shifting
So if I understand you right the arm in relief is at 340 when only the arm is actuated. But it drops to 240 when the boom is lifted at the same time? Are you reading this pressure at the pump outlet? Do you have both circuits over relief at the same time? The LS pressure should be less than main pressure as I recall by about 300 PSI. If the valves are only partially stroked the pump will only put out enough oil to keep the LS pressure at the difference. Since the stick is over relief the pump only needs to supply enough oil to make the boom go up. The compensator will stay closed and the pump will only produce the pressure necessary to raise the boom by the amount of stroke of the two valves. There might be 340 in the stick circuit but you will only see the pressure on the boom circuit at the pump. Try going to max stroke on the boom up at the same time you hold the stick over relief. You should get 340.
John C. you understand right: the arm in relief is at 340 when only the arm is actuated. And it drops to 240 when the boom is lifted at the same time. And I am reading these pressure directly on the oultlet of the main pump. In fact the boom raise pressure before the end of its stoke should be around 170bar and this is indeed what I am reading. But I couldn't find any explanation of the 240 bar as I described below. Anyway, I think that when the arm in is relieved the corresponding pressure compensating valve should be fully open and the boom raise pressure compensator should throttle to make the upstream pressure the same as the arm in relief, am I right? Because the PC valve should throttle on the light load side By the way If I relief the boom raise and the arm in at the same time I read 340 bar also
jey_c I don't have a book for a PC400 but my book for the PC220 shows the main control valve to be split in normal operation with the boom on one side and the arm on the other side. Are you reading both pumps at the same time with two gauges installed? Basically the boom up side should read the actual lifting pressure while the arm in side should read the 340. I'm thinking the compensators won't come into play unless the pump merge divider is shifted so both pumps combine their flow. I also recall the pumps will be destroked when over relief because it will require only enough oil to maintain the flow necessary to hold the relief valve open. The LS differential pressure hits the 300 PSI and the pump backs off until the differential drops below that set point.