Hi to everyone here and thanking you in advance for any help. Have an older Airman AX50U excavator that is causing me grief. Bought it with this problem. Could be an easy fix with someone with experience in Hydraulics. When pressure is put on any of the three boom rams, such as trying to lift machine with bucket,or holding back on dipper or bucket cylinder levers, a high pressure release valve cuts in and stops any pump pressure. The three boom cylinders will lower with levers under gravity but no up. Take throttle to idle and everything is fine again. Full working of the blade cylinder and swivel motor are not affected while nothing else works. Have removed and checked relief valve's in valve chest to no avail. Have had own mechanical shop since 95 and worked on a lot of these machines but have never had much experience with the fine workings of the hydraulic system. Thanks Neil
Hi Neil Are the left and right tracks working ok, both together and independently or do they also loose all power when increasing the rpm? Best regards
Hi Kobi. Both tracks lose all power till revs are bought back to idle. Blade has full power Wired safety solinoid direct to 12 volts. No change. Photo number 2 shows a round valve body with a half inch square shifter. Turn that Quarter turn and the two hand lever controls are reversed? Why would they have that stock standard ? One thing I noticed today was at idle and the bucket on the ground trying to lift the machine at idle, the rear valve bank that supplies oil to the boom is vibrating/ shuddering bad. I have already pulled that release valve out plus all the others and checked. Is the same as the rest. Nothing odd. I’ll swap around tomorrow. Thanks for responding Neil
Hi Neil I suspect that your main pump maybe the cause of the problem but diagnosing this 100% would require a flow meter and loading valve. There is however one line connection to the pump that i would suggest plugging and capping and then check to see if the issue is still present. This line maybe an add-on for a quick hitch valve possibly, circled in pic attached. There is also a bypass valve located in the valve bank diagram that can bypass one half of the main pump circuit but it is not clear as to where this valve is located or its operational purpose. Some export machines did have a 4 way and 2 way pattern changers along with pipe and valve work for auxiliary options when shipped. I would think these would have been requested options by the dealerships at the time of order. Kind regards
Capped off the line you circled but no difference. Swapped over relief valves and no different. Would love to know where that bypass valve is you described. It is more the area of problem that I feel could be it. Allows oil bypass under load and doesn’t release until back to idle. Have pulled out the whole lot but nothing odd. [ATTACH]321639[/ATTACH][ATTACH]321640[/ATTACH]
Hi Kobi. All Good . After spending 2 weeks switching around relief valves, swooping hoses, Hooking up pressure gauges and going through parts diagrams, I tried switching over the two main pressure hoses coming out of the pump and it worked. Don't know why and I don't care. Is fixed and I'm thinking this machine may have had this problem for a couple of owners before me after an odd comment. Thanks anyway for all your kind help. Cheers Neil
Hi Neil No problem , glad you got it sorted in the end and thanks for the update. I looked into that bypass valve but its actually a flow combiner valve and I couldn't see how this could be the issue based on your description of faults so I didn't want to suggest checking it and wasting any more of your time. Main thing is that you got working again. Thanks Neil best regards
Hey Kobi. No good. Still the same Went to move machine yesterday and under tracking, hydraulic power was lost. Anyone good with schematic drawing puzzles? My head has fallen off my shoulders.. Here are the details of the dramas of this little Hitachi 5 tonner. You may be able to sort this puzzle by the diagram. When trying to lift the machine off the ground with the boom cylinder , a high pressure release valve cuts in and stops any pump pressure. Same as when operating bucket cylinder holding under pressure. The three boom cylinders will lower with levers under gravity but no up. Take throttle to idle and everything is fine again. Full working of the blade cylinder and swivel motor are not affected, while nothing else works. Have removed and checked relief valve's in valve chest to no avail. Hydraulic pump showing 3450psi Had so called Hydraulic expert out for 5 hours. Too Hard Swapped over the main feeds V and N and things changed. Can lift the machine off ground and work the bucket cylinder with no problems. Thought I had fixed it. Except now when I track the machine the same problem occurs as before. No hydraulic power to three boom cylinders while full power to blade cylinder and swivel motor. Head is starting to spin…
Picture you see are after swapping over N and V
Hi Neil Did the hydraulic technician give any test readings of system pressures for each function?. By your description its sounding like a pump issue as the problem did change slightly when you had initially swapped the main pump hoses n and v. For testing to see if the pump is a problem you would typically need a flow meter and loading valve. Here is a suggestion if you don't have any test equipment , It involves swapping 2 pump lines similar to what you had done before. Due to hose length restrictions it may be difficult or impossible to do. Try connecting the main pump hoses back to how they were originally and get the machine to fault with the travel right lever only. Now I'm assuming that when the machine is taken to high engine rpm the travel right lever will not operate the track motor and the machine will not skid on flat hard ground unless the machine rpm is take back to idle. If this occurs then try and see if you can swap the pump hose connections I have highlighted, you may need some 1/2 " fittings and an additional 1/2" 2 wire hoses to make this happen. when you have swapped the lines test the machine again and see if the track skids or if it just stalls. If the track does skid and appears to work then don't test any further as by swapping the 2 pumps exposes the smaller pump to a higher relief pressure. For short testing operations this will be ok to do but any extended operation where you stall the function to full pressure repeatedly can have the potential to damage the gear pump when exposed to too high of a pressure for too long. if during the test the track can skid at full engine rpm then the problem is the main pump. If the problem is still present then the issue goes back towards the control valve. I have attached some information that will hopefully help in getting the issue sorted going forward.
Thanks Kobi Job for Monday