Hi everyone, i need some advice on getting to the problem. I am a diesel mechanic and not an earthmoving mechanic so my knowledge on hydraulics is limited. I am fighting with a Doosan mega 400v that is not turning, wel? It can turn but the steering is extremely hard. So far i have replaced the orbital valve with yet another second hand one that i don't know if it works, that doesn't make a difference. I then removed the pipes from the steering cylinders but the steering remained hard and both pipes had pressure/flow. Then i removed the left/right turning pipes from the orbital valve, now the steering is soft but still both pipes have pressure, and if i am correct those are pilot pressure to open a valve supplying bigger pressure to the steering cylinders. Any help would be greatly appreciated.
Hi there, You likely have a stuck flow divider/priority valve (flow amplifier) Valve under the cab, 3 larger lines attached, and 2 small load sense lines. The pump supplies flow to the brakes first, when you steer, a signal is sent thru the LS line to shift the spool over, flow will go to the orbital. I would "T" into the LS and see if you are in fact getting a signal from the orbital. Also seen a failed brake valve, sending a constant LS signal. Make sure that the pedal is returning all the way. Hope this helps.
Thank you for your answer, i have noticed something else so i don't know if your suggestion might change. The orbital valve is getting pressure, so much that the pressure pipe is stuttering? Don't know if that is the right description.
The orbital valve is supplying signal pressure to two valves, first one i take is the priority valve then the second one is a smaller valve that takes pump pressure from the first valve to the steering cylinders. If that makes any sense
Well, if you are finding the pressure line 'stuttering' you might have a pump problem, or the unloader that is in that circuit (directs flow to the main circuit, or back to tank if nothing is actuated) Please understand it's been about 10 years since I worked on the steering system of a Mega V, they use a Denison vane pump. T67DB series. Constant flow. They fail pretty rapidly (go from perfect to OMG *** rapidly) I would suggest that you might have a vane stuck, best way to test is a flow meter. I installed the flow meter on the inlet to the flow amplifier (the LS line goes to it from the orbit) My old notes tell me it should have 190L per minute. If you were to 'T' in a pressure gauge while steering, it would spike a little with a failed pump (low pressure) but spike a lot with a failed unloader valve (high pressure) The unloader is on the frame, R/H side, think it has 4 pressure lines and a return to tank. that is where the multiple pump flows are combined. This is the point it can become VERY complicated, there is a relief and 4 check valves in that unloader. I know steering is a tough thing to troubleshoot, the test gear is expensive and swapnostics eats time. hope this helps
Thank you!! The flow amplifier was stuck like you said. I removed and opened it and it was full of rust and pit marks. Gonna replace that and hopefully all my problems will be fixed. Thank you so very much.
Happy to help!
I have another question if i may, any idea what the steering pump pressure should be? I can't seem to find convincing info on Google.