I've been working on a MDI 140 BLC, which is the same as a Kobelco 905LCII. All functions tied to pump number 1 (closest to the engine) are almost non-existent until you stroke a function from pump number 2 and as long as you keep pump 2 stroked everything works. Pump pressures are good but the negative control pressure to pump 1 is very low. Should be 400-500psi and I have 150 psi. The troubleshooting section in the Kobelco manual says that this could be caused by a problem with the low pressure relief valve. I've located the negative control relief in the schematic but cannot find anything about the low pressure relief. Does anyone know,is it possible that these are both the same valve? Or is there something else I'm missing?I've not done alot of work on the older Kobelco excavators and the manuals leave a little to be desired. Any help would be appreciated. Thanks.
Sounds like a broken spring in a relief valve.I have a shop manuel for a 140 b if you need anything i can try to help. Quentin
I just looked in the manual and there is a minimum flow signal circuit.Neutral cut valve 77.If this circuit isnt grounding when load is sensed it wont stroke the pump.It is for fuel consuption purposes it controls the variable displacement pump.That sounds like it could be something to look at.
If your problem still persists, provide me your serial number and i will work with you to solve. I can also e-mail tech info. I have all available at my finger tips for any yutani. The way a yutani/kobelco generally works, at least just before the present models of today came out on the market, is that when a function is operated via the joystick controls - either the spool being shifted or a pilot signal tee'd at the spool directs over to allow confluxing of the secondary hyd pump to join the circuit by shifting what kobelco calls a bypass cut spool that brings the pump on-line. This is accomplished thru the bypass cut spool shifting over and blocking the hyd pumps' neutral oil flow from going back to tank (~ to an open center) which the netral oil flow normally goes across the negative control relief valve (neutral relief). The neutral relief spec creates 450 - 650 psi. This is seen at the hyd pumps' regulator valves (on a 140blc the two blocks that are located untop the pump case). You can simply tee into the single pilot lines on both pump regulators to read values with a 1,000 psi gauge in neutral and while functioning the machine to get a better idea of what's going on. And in this case what is not. As the bypass cut shifts the pressure in the pilot line will decay off gradually. The pump regulator then works to stroke up the pump oil flow. Do not forget pressure is a resistance to flow. A pump just pushes oil. All kobelco pilot line fittings are of a jis (japanese industrial standard) 30' cone with bspp threads (british standard paralel pipe). # 4 jis male (30' cone) the 2 other points you can gauge are on the side of the pump. 1/4 jis bspp plugs. Pump outlet use 6,000 psi gauges. Facts; boom up is two pumps. Main pump p1. Boom down one pump ( p1 closest to the engine ) arm in & arm out under load ( two pumps ) main pump p2, initial arm in air digging will be only one pump p2 until the oil pressure builds and p1 confluxes into the circuit. Bucket is p1. Swing is p2. R/h travel p1. And l/h travel p2. The travel spools block oil path to tank, bypass cut spools are not needed. A quick check if you suspect the neutral relief, they are identical, swap and if the other pump reads low, you have found the problem, however, i suggest buying two new valves. I do not suspect this is the problem for if the neutral pressure is low your pump will be turned on at max flow. I think you might have a valve that is not shifting. Or a pilot pressure signal is leaking off past a shuttle ball not causing the shift, or your main relief is buggered. On the yutani/kobelco there are four main reliefs. Two in each pump output lines within the main control valve. The two at the back of the valve in the mid section of the valve are the travel reliefs spec to limit system pressue to 5,000 psi. The other two one on each end of the block ususally one untop and one diaganally across on the bottom of the valve are the attachment reliefs. Boom. Arm and bucket system reliefs. 4200-4400 psi. The swing reliefs are on the swing motor itself 4000 psi. Each spool boom, arm, bucket & travel motors have overload port reliefs, a safety backup to protect the leg of that circuit when the spool is not shifted 5300-5600 psi. If these are good they never even open. Long winded, i apologize. Let me know if you still have a problem.
Thanks for the response, I apologize for not finishing this thread when I solved the problem. This machine has auxiliary plumbing on it and for what ever reason, someone had looped a hose from one line over to the other. So all the oil from one section of the control valve was going directly to tank. Removed the hose and the machine works fine. It took a bit but I figured it out, sometimes it's the simple, little things. Thanks again.
Cool. That would definitely do it. Take care.