I have a PC 340 dash 7, with low hydraulic speed. while checking hydraulic pressure at arm in relief using pressure gauge , i have the following result: on the front pump the pressure is 365 bar and servo input 180 bar, and for the rear pump the pressure rises slowly to reach 365bar and also the rear servo input rises slowly to reach 180bar. i don't know why the rear pump pressure rises slowly while the front rises immediatly, i think this slow reaction of the rear pump makes the machine slow. If you have experienced such behavior please reply.
Where are the big guys in hydraulic, come on. Any idea?
I've seen that in Dash 6 machines but usually when trying to figure out some other issue. There are a couple of things to think about. First, the arm in had a regeneration valve in the Dash 6 line that gave lots of problems. There were many updates on that valve. It usually caused a loss of pressure and low power on easy digging but when a lot of resistance was felt at the bucket the regen would seat and the stick would suddenly have all kinds of power. The next thing I can remember is that one pump was primary for arm in while that other pump usually lagged like you are describing. Have you run a cycle time on arm in and out and checked that against the book? We didn't see the phenomena as being a problem most of time. The last thing I can think of is the LS differential pressure for the lagging pump may be off or there might be a problem in the valve itself. i'm not familiar with the Dash 7 line but in the Dash 6 line the LS valve was a cartridge that screwed into the side of the pump. If the Dash 7 line is the same you could swap cartridges between the pumps and see if the lagging pump changed with the valves. I would think though that you would have seen a difference travel with the machine veering off to the slow pump side in an uphill walk. Let us know what you find.
Hi john, here what i found after testing the machine again. In fact, the rear pump is lagging not only at arm in relief but also when bucket, boom or the corresponding track are relieved. After this, I interchanged pumps and I noticed that the front pump is lagging while the rear one is now normal. I think that the problem is located somewhere in the main control valve. Could it be the the pressure reducing valve or the sequence valve inside it? Because the pump feedind this valve is the one lagging. THANKS
This problem I have seen in the Dash 6 line a lot, particularly in the 200 series models. What we found in the past was the LS valve had some kind of problem, either in the hose supplying oil to that valve, the orifice in the main valve having something partially blocking flow or the LS valve itself. The LS valve in the Dash 6 line is the valve on the pump that has a small hose coming from the main valve. I have taken the LS valve out of the lagging pump and carefully taken it apart to check on the springs and seats but didn't find anything visibly bad. When I installed the valve back in the machine everything went back to working. I have also swapped the LS valves between pumps and still had the problem and sometimes the problem went away. Sometimes just taking the hose off and blowing it out with air pressure solved the problem. I usually just took the ends loose and put the air nozzle on the pump and blew back. Some times nothing seemed to make the pump work and it just started working for no reason. All I could figure is that trash was getting into the load sense circuit through a compensator somewhere on that side of the main valve and partially plugging the outlet orifice to the LS hose. Hope this helps but Komatsu never revealed an answer to this problem. They were like that even with their dealers most of the time. If you call a dealer and they tell you they haven't heard of this, they are lying.