Hi Guys, I am dealing with an issue, have a troubleshooting job of sennebogen 825 scrap handler, The issue is During closing the grab it has not enough power to grip and press the material (seems like hydraulic pressure is bypassing from somewhere i did the back pressure test too it should be 250 bar but its actually 110 bar and during opening the grab the pressure is at standard 250 bar) Any clues? From where the pressure is actually bypassing? (One more thing: i have observed when we open the grab and leave the operational lever, the grab cylinders start drifting very fast and end-up being in a closed position i also thought that its all related to cylinder piston seals but customer said they have also replaced the grab with new one to check but faced the same issue “Loss of power”) Thanks.
A few questions. Did this happen all at once or gradually? When you said "they have also replaced the grab with new one", did they install an entirely different grapple including the swivel? Is the proper attachment (grapple) selected on the tool selection display? Do the grapple hoses attach to any other valve at the end of the boom? Has the valve been reprogrammed for any other attachment? I agree that generally speaking when the paddle cylinders float down under there own power this usually means an internally leaking seal but installing a new unit disproved that. I would be looking into the grapple valve as either being contaminated and not allowing the spool to travel it's full stroke or a problem with the pilot control. And don't discount the possibility of a part of a seal in one cylinder contaminating the valve thus causing both problems.
Do you have a service manual for the machine? It is likely to have a troubleshooting tree to help you find the problem. A schematic of the circuit would tell you how the system works. The cylinders drifting down would mean the problem is more that likely in the cylinders themselves. Put together your troubleshooting plan. I like to start with the easiest and cheapest possibility and work toward the more difficult and expensive items. Pull the return filters out and check for metal and soft material like packing. Then maybe check the cylinders by listening to them while the operator is holding them closed. You might hear the oil whistling or making some other noise. I suppose there is a rotary manifold or swivel in the grapple that would allow it to rotate. Try opening the legs and then pushing on one leg to rotate the grapple. You shouldn't be able to do that. If so then there is likely a problem there. If all that checks out good then work your way back to the control valve. Does it have a cartridge relief on each open and close circuit. Try swapping them and see what happens. You usually want the open side to operate at a lower pressure anyway. I am curious so let us know what you find. That brand of machine is not very popular in my area.
Thank you so much, BILL.G and JOHN C for your responses, The grapple and its swivel is a single piece assembly and i don't see any special valves in the schematic in the line for grab opening and closing cylinders which is coming from the control valve, Also as Bill g said the customer has removed the complete grapple assembly to check the issue (so the doubt about the junction block (which supplies oil to its 5 cylinders also equipped in a grapple assembly) had gone) . And as suggested to check the return filter so the issue is happening only in one operation not in any other one and i guess We could could doubt on it if we were facing the issue in all operations. Also i am sharing the schematic of this machine (find attached) for you guys to consider it regarding that issue and kindly share your suggestions. Thanks again.
If you have an hydraulic flow tester it would be easier to diagnose the problem. Also check the pressure sense valve that is in combination with the grapple directional valve, if it doesn't open completely your flow will be low. Many of these auxiliary valves are cartridge and maybe a little difficult to test. I would go to the pilot system first and verify the pressure because if it is low you will never see full operation.
Ive tested the pilot pressure already its On standard. But as you said about the travel of the spool of main control valve that it could be stuck or not taking complete stroke. Ive actually took the complete spool out to check if it has any wear or its stuck but nothing abnormal observed the spool shaft is smooth and easily gets out. Also have you saw the hydraulic schematic which i have attached?
I looked at the schematic, the reason I asked about the pressure sense valve associated with the grapple valve. Did you inspect it?
In the schematic: it is shown that the line which is coming from the control valve to open and close the grab has no any additional valve in line and also the shown relief valve which relief value is 245/300 Bar as shown in schematic. (This valve is inside the control block) Are you talking about that valve?
The valve marked R900894752.
Hi Guys! I have made a re-visit on a machine for same troubleshooting, but this time Operator told me that he is observing that all functions are slow, Then i re checked all functions back pressures. As per schematic grab closing pressure should be 300 to 350 bar. (As per test its showing 50 bar in closure but during checking, sometimes it showed 100 bar at full load but as i leave the lever and re operate it gets back to 50 bar at full load) Grab opening Pressure should be 250 to 300 bar. (As per test its showing 300 bar constant) Boom standard pressure should be 300 to 340 bar. (As per test its showing 200 bar constant in Extend and retract same) Outrigger Standard pressure should be 300 bar. (As per test its also showing 200 bar constant in extend and retract same) Stick Pressure standard pressure is 300 to 340 bar. (As per test its showing 300 bar constant in extend and retract same) My colleague try to re-adjust relief valve to increase the pressure of Boom and outrigger but no any difference observe. But when he adjusted the grab closing pressure its goes up to 50 to 100 bar (Constant) at full setting of relief valve. I have changed the boom Relief valve just for checking but no difference observe. I have tried to re-adjust the LS (Load sensing) relief pressure but no difference observe. but i am still in doubt that there something wrong with LS signal in those control block sections in which we are observing 100 bar drop. I cant blame the pump because stick and grab opening pressure is still at standard 300 bar. also one more doubt is internal leaking in cylinders. i have re argued with customer to put the Good Grab assembly for checking to re confirm internal leakage in cylinders. Looking forward for your valuable suggestions.
You have internal leakby inside that LS system. Should be a pilot operating control on the gab head, as move to open it allows close side oil to port off and opposite moving to close. The pilot system is likely contaminated or a pilot valve (Usually ball poppet) spring is broken. Can be a component part of the cylinder(s) themselves. One corrupted will affect all if more than one on Grab.
In looking at the schematic the system looking a lot like a Komatsu hydraulic system and what you are describing sounds a lot like you have a leaking pressure compensator. Following you explanation you have a pressure problem on boom up, grab open and outrigger both ways. Here is a quick test. Since the stick seems to work normally operate the stick over relief and see if the grab pressure changes. Then do the same with the boom. You could also try running the outriggers with the stick over relief and see if that changes the pressure, although I suspect it might just need to be adjusted. The pressure compensators are simply load check valves with load sense pressure put on the outlet side of the check. On Komatsu excavators if one leaks, usually the pump output will be affected. The Sonnebogen system looks just a little bit different though. Have you done any cycle times?
Thanks you for your responses, i have already checked the Pressure compensator only boom section. its nonadjustable and fixed type when i removed it for checking it looks normal springs and spool both are fine. as you suggested that test i understand that you suggested to verify the compensator issue, but if i use the faulty function (for Eg. Boom) over stick relief what i have to expect to verify the issue. And No i didn't check the cycle times. also this Crane has Rexroth M7-22 Control block i have attached its manual also please find in attachment.
You know the stick function gets full pressure. What you are looking for is the pump pressure dropping to the low boom pressure or the boom pressure working at the stick pressure. The cycle time will tell you if the LS pressure is getting back to the pump. If it isn't getting back to the pump the cycle time will be slow. You can also find a place to plumb a gauge into the LS pressure. If the LS pressure is low the pump will only stroke up to the low pressure.