Hello everyone, this is my first post on the forum, so I hope I’ve followed all the rules and written it clearly enough. I’m having trouble with an excavator Yanmar B12 with pilot joysticks . This type should be similar to the B14 and B17 , year of manufacture is before 2000. I haven’t been able to find a service manual for this type of excavator with pilot joysticks. However, I managed to get a manual for the mechanical joystick version, which helped me in other steps, but not with the pilot circuit connection. I bought the machine to save it from being scrapped. The regulator BLOCK MHSTE5G10/30 for the pilot joysticks was missing. I obtained this block and connected it according to the parts list from the official Yanmar website, see the component diagram and relief (1 and 2) . I connected it directly to P1 and P2 on the main control valve . The regulated pressure Pv I split using a tee for both the right and left joystick. From this block also comes T , which I connected according to the parts list to the return line to the tank, which carries the T from the swivel joint , and also the T from both joysticks. After I started the machine, I found out that the main control valve does not have pressure on P1, P2, and P3 during normal operation. According to the diagram, the valve should be open , so in fact, the section with P1, P2, and P3 is not pressurized when it’s not being used. In order to pressurize the BLOCK MHSTE5G10/30 , I pressed the P.T.O. pedal , which has a mechanically operated valve. The P.T.O. pressurizes sections P1 and P2 . The section for P1 and P2 is shared; the section for P3 is separate (see the diagram). When I press the P.T.O. pedal , the P1 and P2 section is pressurized to 160 bar , which corresponds to the value in the service manual. This pressure then reaches the BLOCK MHSTE5G10/30 and is reduced to about 30 bar for the pilot joysticks, and then I am able to operate the machine. Which isn’t ideal, though, since you have to hold the P.T.O. pedal to be able to work. Therefore, I’m interested in what the other valve from the parts list might be, because they aren’t described in more detail, and perhaps that could solve my problem with the main control valve , which is in the open state, and maybe some valve closes the main control valve , which would pressurize it and give me pressure for the BLOCK MHSTE5G10/30 . In the parts list there are two types of configurations — one with BLOCK MHSTE5G10/30 , and another valve shown, which in my opinion could be an electrically controlled valve for safety , when the left joystick is folded up. But that still doesn’t solve my problem with the pressure — because the main control valve is open (see the schematic for the mechanical joystick version) — and I don’t know how to pressurize section P1 and P2 to have pressure for the BLOCK MHSTE5G10/30 . Then, on the second parts list relief (2) , there is also some valve that I don’t know what it is. BLOCK MHSTE5G10/30 is on both diagrams, but on relief (1) the BLOCK MHSTE5G10/30 isn’t shown as it actually is on relief (2) . On relief (1) I find the connection of that unknown valve rather strange, as it’s only on one side of the T for the pilot joystick. The machine was originally designed for pilot control ; I’m not converting it from mechanical to pilot — pilot control was already on it. The excavator has a three-section gear pump – P1, P2, P3 – and no pilot pump . There isn’t one even in the parts list, so I assume that the BLOCK MHSTE5G10/30 is powered directly from P1 and P2 (see the parts list). The main problem is where to create pressure for the BLOCK MHSTE5G10/30 . If anyone has experience with an open main control valve and subsequent connection of pilot joysticks, I would really appreciate help or ideas about what might be incorrectly connected or what could be missing. YANMAR PART LIST: https://yparts.yanmar-compact-equip...ent/Y00S2983B12CR(H)/catalog_id/MAC_B12&YCEE/
You've done impressive detective work! The issue is you need a way to pressurize P1/P2 continuously, not just when the PTO is engaged. Early Yanmar mini excavators without dedicated pilot pumps used a pilot cut-off valve or load-sensing valve that keeps a section of the main pump pressurized when pilot controls are active. The mystery valve in your parts diagrams is likely this component. Your options: Find the missing valve: Check parts diagrams for "pilot cut-off," "safety lock valve," or solenoid-operated spool valve between pump and main valve or Jury-rig solution ( temporary ): Install a manual ball valve on P1/P2 to create pressure—close it for operation, open for tank relief. NOT ideal long-term
Thanks for the reply. I know that pressurizing P1/P2 using the P.T.O was only used for testing the pilot joysticks. I’d like to find the missing valve, but the problem is that in the last link I sent [YANMAR PART LIST: https://yparts.yanmar-compact-equip...ent/Y00S2983B12CR(H)/catalog_id/MAC_B12&YCEE/ ] — the original parts list for this machine — it doesn’t have a proper name, it’s simply labeled as “valve.” If it is the pilot cut-off valve or safety lock valve you mentioned, then when I look at the relief(2), the pilot cut-off valve does not pressurize the open main valve — it’s simply a safety valve for getting on and off the machine, and according to the parts list and connection diagram, it doesn’t make sense that it would be used to pressurize the BLOCK MHSTE5G10/30. It would rather help me to find a hydraulic circuit diagram that shows the open control main valve together with the pilot joysticks. So far, I’ve only found diagrams where there’s an external pump for the joysticks. Do you know of any machine that should have a similar connection and that has hydraulic documentation available? I don’t want to make a jury-rigged solution — I’d have to redo it anyway with a proper setup. I’ve also seen a solution where there’s an outlet section with a backpressure valve. The problem is, it seems similar to a jury-rig solution, and moreover, I haven’t been able to find this part anywhere. That’s why I came up with a different solution, as shown in the attached diagram: using a relief valve with 30–50 bar connected between the P1 pump and the control main valve. This way, I’d actually pressurize the line for the joysticks before the control main valve, and once the relief valve exceeds the set pressure, the excess flow would go to the control main valve, which would remain open as before. What do you think? Will this affect the pressures in the control main valve? I think it won’t, because the P1 and P2 sections in the control main valve are shared.
For reference, I’ve attached a picture of the entire main control valve. From what I can tell, if the pilot joysticks are supposed to get pressure, it would have to be done by restricting the return (tank) line — that’s the large block with the thick black hose. According to the parts list and exploded diagrams, it doesn’t seem possible to pressurize the circuit just by using a pilot cut-off valve. So if I were to install a pilot cut-off valve, I guess it would have to go between the pump outlet and the main control valve, but I’m not sure it would work the same way on this setup. That’s why I’d rather go with a solution using a relief valve instead.