Hi all, In this case it is Fiat cobelco e200sr, but I have seen this problem with other brands as well. It happens on dipper or bucket cylinder. When closing, arm pauses in vertical position for about 1-2 seconds before continuing to close. It sort of swings a little as well. I know that in this position weight of the arm stops pulling the cylinder piston and needs to be forced to continue closing. Nobody ever asked me to rectify this problem, so I don't know what can cause this. And would like to find out for my own peace of mind. So, if anyone cares to explain.......thank you!!!!
Hitachi UH series had a flow adjustment up on the boom just behind the mount of the dipper ram. That hesitation could be eliminated, it was on the steel line for the inward stroke of the ram. Other Japanese diggers of that era may have had this also. Iikley causes was the pump wearing and not pumping sufficient flow or worn ram packing. Hope this helps.
Thanks for the advice!!! Movements have plenty of speed, so I don't think it's the pump in this case. Worn cylinder can be a problem. But it does have that controlling block bolted to the cylinder. I'll see if they let me play with it. We'll see if anybody else chimes in with some suggestions.
Worn cylinders will also have the evidence of cylinder drifting problem.. The entire standard cycle of arm closing from end to end might be about 4 to 5 sec. Additional 1 to 2 sec pause in vertical position is indicative of slower arm speed. So, if all other speeds are okay, proper flow demand for this specific operation may not be there. Most of the machines will have a regeneration circuit whereby the exiting oil from rod end side flows back to the bottom side of the cylinder to make up for the flow demand and can cause problems... Is there any abnormality in operating pressure while operating arm in idle..
This is a fairly normal problem on excavators, the weight of the dipper pulls the rod out of the cylinder faster than the oil is supplied to the piston side of cylinder, the pause in movement allows the oil flow to fully fill the cylinder. Some excavators have an adjustable throttle valve mounted on the cylinder rod side oil line to restrict the return flow thus eliminating the pause in movement. On the bucket circuit it is normally noticed when a heavier bucket or attachment is fitted. If there are no other problems apart from the delay when the arm is vertical then I would be confident that your pump and cylinder are not at fault.