Hello. I have a 2004 Yanmar VIO 50-2 with 3200 hours on it. Was using it yesterday and suddenly the blade and swing functions both became very slow and weak. Everything else is working as it was, with good power on the bucket, boom, arm, etc. Of note, I recently rebuilt the swivel joint, and the blade maintains it position just fine so I don't think the swivel is the problem. In other words, if I used the boom to raise the machine and lower the blade (as the blade is too weak to lift the machine anymore), once in position, the blade will maintain that position without sagging. Also, the swing motor doesn't cross the swivel joint, so I'm ruling that out as a potential cause. The gear pump on this machine pumps oil for both the swing and the blade, and is supposed to be at 3555 PSI according to my service manual. There is a port for testing at the output of the pump and I did so. I am getting about 1200 PSI in both low idle and full throttle with blade down pressure. (Side note: once when testing at full throttle, I briefly got higher pressure though still low. The reading was bouncing around a bit between 2000-2500 PSI while the cylinder was at max extension and not moving, but immediately upon trying again and several more times, only 1200 PSI max.) Also per the service manual I located the pressure relief valve for the gear pump which is on the end of the control valve block and actually easy to access. I also traced the hose from the pump to verify this was the correct PRV. I adjusted it in both directions and there was no change in the pressure. My conclusion: The gear pump is failing, and needs to be replaced or rebuilt. Is there anything I am missing? Many thanks, Jon
Good day That looks a very through checking out of the gear circuit, I would drop the bucket into a trench and just check the slew pressure left and right.The low pressure is down to leakage can be the relief valve or pump. I suggest take out the relief 12 and see if there is any obvious cause of the fault first before pump replacement. Kind regards Uffex
Thanks for the reply uffex. The PRV you indicate labeled 12 is also labeled R3 (Relief for pump 3, the gear pump), and that is the one I was adjusting which made no difference in the pressure. Agree a relief could be the problem, and I don't think it would be a relief on one of the individual control valves because all 4 functions are affected (swing left, swing right, blade down, blade up and all weak). Therefore I think this relief (R3, 12) could be the only culprit. When you say "take it out" what exactly do you mean?
Good day Jon I suggest you remove the relief look for damage to O rings and blocked orifice, attached some basic information that may be of help. If one of the other inlet sections has the same RV you could switch to be absolutely sure. Otherwise it does sound as if the pump is at fault. Kind regards Uffex
Doh! You meant literally remove and inspect. Sorry for the stupid question. I will do that and let you know what I find. Thanks again.
The best I can remember there is a relief around on the back side of the pump that can get trash in it. Also. Those gear pumps do fail. May be worth a look inside.
This may sound silly but I have seen this issue many times on different models, the dirt inside the machine prevents the valve to open all the way Just throwing that out there start with the basics
I removed the PRV (R3) and everything looked good. I also decided to swap it out with the PRV for one of the piston pumps (R2), which is the same valve and adjusted to the same PSI. That made no difference in the symptoms. So it has to be the gear pump. Going to tear into it soon and see if it can be rebuilt or if I will need a new one.
Good day Jr Most gear pumps do not justify a rebuild, so low cost does not justify the work involved but check it out for yourself. Maybe a good precaution to get a contamination check on the fluid, and bleed the fluid before commissioning the pump. A great policy is to run the pump at low speed for twenty minutes without any pressure. This will allow any micro contamination to flush through to the filters. Kind regards Uffex
I removed the gear pump and opened 'er up. Sure enough, there was obvious wear in the shafts and bearing surfaces, and as you said, nothing that would make sense to rebuild. I was able to source a new (but aftermarket) one for $350 and I put it in today. I adjusted the PRV to 3550 PSI where it belongs, and the swing and blade are back to normal, even stronger than before actually. I did run the machine for 20 minutes to allow the filter to remove contaminants before operating any functions. The oil was quite new, and I still have some work to do on the travel motor, so I will get that done before changing to new oil and filter. Thanks a lot for your help.
Good day Thats great for you to keep the folk informed, so many just dissapear from the radar. kind regards Uffex