Help, I have a kobelco sk25sr-2 mini excavator. It had thrown a rod and was sitting for several years before I got it. I put another engine in it and got it running. I have 500psi on the pilot pressure line from the pilot relief valve, through the joy stick controls and back to the main control valve. ( I'm testing the bucket valve because it's the easiest to access) nothing will work but the blade and turn table. ( they work separate from the pilot control system. Does anyone know why I can't get movement on any other function?
Let me clarify: you do have pilot pressure right at control valve actuator(s)?! Is your hydraulic lock out activated? Meaning is the lever on the left down?
Yes the leaver lock in engaged and letting the pilot pressure to move through the joy stick controls and all the way to the main control valve. I took the pilot line lose that goes to the main control valve and hook a pressure gage to it, it readies zero until I move the joy stick for that movement ( bucket function) pressure gage goes up to 500psi which is what the book calls for. However when I hook it back up to the control valve, it won't move the bucket nor will anything else work. Tracks won't move, arm won't move, only the blade and turn table.
By the turntable you mean the whole upper structure ( like big excavator) or just a boom swing? Obviously you have manual! Look in to hydraulic diagram, you basically have three main pumps: two piston ( inside the same housing, that’s why there’s two outlets) and one gear. I am pretty sure blade is getting run by gear pump. Look if whatever function is operational ( slew or swing), if it runs off of the same gear pump - you might want to start testing the piston parts of the main pump(s).
There are 4 outputs from the pump, output 4 goes to rhe pilot, output 3 goes to the main control valve and workers the blade and slewing (turn table swing) output 1&2 go to the main control valve as well and work everything else. I put a pressure gage on P3 and get zero reading until I move the blade up or down or swing the upper unit. When I put the pressure gage on P1 or P2 test port I get zero pressure even when I move the joy sticks. I have pilot pressure going into the main valve but it's not making the spool move in the Valve to allow the fluid to move to the cylinders.
If your P1 P2 is a piston pump ( usually is) then your piston pump(s) crapped out! Unless you are lucky SOB and compensator spring is broken and rotational group in OKish condition. I wouldn’t bet on that! Though.
If you want to make sure I am right - just restrict the P1 and/or P2 ( plug the hose that goes in to control valve). And read the pressure.
I switched p3 with p2 (only hoses that would reach each other) and it worked the blade and swing just like p3 did originally. Acted like it had good pressure, picked the machine up with no problem. With that said, it acres like all the pilots aren't shifting the spools and the pressure from p1&p2 are going straight back to the tank. Should p1&p2 be reading pressure in a neutral position?
Well! That’s interesting!!! Is there a reason spools will be that stuck? At least pressure test P1 P2 separate from Control valve, to know both are working good! I had one spool getting stuck because of debris from damaged cylinder, but never seen all of them stuck. That valve is open center, so there will be no pressure build up until you move one of the spools to block center passage. If you pretty sure that piston pumps are. Hold down a minute!!! Check your diagrams how auxiliary connected and combined, check if someone didn’t connect auxiliary hoses to each other. If P1 and P2 combining flow to run auxiliary, and hoses are looped - that might be your culprit.
Not sure if I'm following you, p1,p2 & p3 come straight off the pump and go directly to the main control valve. I did loosen the hoses from the bucket cylinder, cranked it up and got fluid poring out of one side like it was under pressure (with out touching any controls) i cut it ok, hooked that line back up to the cylinder, cranked it agin and this time fluid pored out of the other line without touching the controls. I thought that there shouldn't be any fluid moving at all from these lines until I moved the appropriate joy stick.
By auxiliary connections, do you mean the lines at the end of the boom near the bucket for like a thumb?
So I don’t have exactly yours diagram at hand, and I don’t work for Kobelco for 20 years to remember it. i worked on some mini excavators, and they are similar and different at the same time. The pumps set ups pretty much the same , but combination of the controls and control valve set ups are different! This one have trochoidal pump just for the pilot, most of them combining branches flow from two or all three pumps to create pilot. All 4 of your pumps, including piston ones, are fixed displacement, that’s why all parts of you control valve is open center! Many of these machines combine flow from two different parts of control valve to run high flow for auxiliary attachments. If your P1 and P2 combining the flow for auxiliary, and something is connected wrong or got stuck - it may dump all your flow from both parts of control valve back to tank without building up the pressure. Yes.
No sir there's nothing connected to those ports at the end of the boom. Is there a way to check pressure on p1&p2 ? If I unhook them and connect a gage to them, won't it bust something do to no relief valve to let the fluid go somewhere? Also thank you for taking time to trouble shoot this with me.
No, the compensator spring will not let you over pressurize the piston pumps. But don’t do it to P3 though!!! I don’t like to use plugs, I use needle valves.
I am not about to buy manual just to help you, but that’s the best I can find for free. This valve combining P1 and P2, but I can’t really read diagram because of bad quality.
I can’t really see it good, but it just might be that failure of the one main relief may affect the other! Or something happened to both main relief valves.
Upon ruining my eyes to look at that blurry diagram, it looks like that valve combining flow of both pumps to run boom. So if something failed in the boom circuit, and that valve is in the combine position - it can dump the pressure of the both pumps. JCB has the kinda same thing for aux. flow, and as far as I remember arm crowd up to certain pressure.
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does that help? I'm still trying to learn how to read it. Somethings I get and some are like Chinese arithmetic!
OK, it is travel straight spool.
Yes, it is a lot better!
Was dozer and slew levers pretty stiff? Do you have water in the oil? Was it sitting long?!?! I have a hard time believing that all the pilot operated spools are stuck, unless they are really rusty! But I guess you can try to take bucket actuators out, and pull the spool out and inspect it. Let’s do that and see if it will help, if it will - you gonna have to do the same to rest of them.
No sir, dozier is cable operated with leaver, it is strong, the slew turned fine by the left joy stick. It also moves quick and strong. It sat outside in the weather for several years is my understanding. The guy couldn't fine an engine. All the hydraulics were hooked up and intact. I pulled the engine and pump together. The guy said that they were working it when it threw a rod. It's hard to believe that everything that works off the pilot control is not responding. Not even a little bit, you can't feel anything in the joy sticks like it's even trying to move. What would cause the fluid to pour out the lines to the bucket cylinder? I haven't tried un-hooking any other cylender.
I think I need to make sure that I have 3270psi on p1 & p2 and if I do, then do what you said about taking one of the valves out to see if it is in fact stuck.
If it was blind end hose, just a back flow from return gallery infused by return filter resistance flowing back through check valve (circled), it means pump has a flow, just wouldn’t build up a pressure, because it gets dumped some where else.
Probably pull both main reliefs for P1 and P2, inspect the valves and O rings on them! You already know that P2 building up a decent pressure!
ok I'll do some more checking and get back to you if that's good with you. Thanks agin for your help.
So that straight travel spool first allows you to use other functions while travelling, but it called straight travel because it evens out the pressure on both travel motors by connecting both sides of the control valve, and affectively flow of both pumps, and doesn’t matter which side you using additional functions on while travelling - both motors receives same flow at the same pressure.
Yea! It is fine! Just when I am busy I will not respond right away.
TVA, You were right, I took the bucket pilot line loose, took the pilot cap off, pit the pressure gage on the pilot line I took off (I left the other line hook up) cranked the unit up and worked the joy stick a few times both ways. Then it happened, I saw the spool valve shoot out alittle and the bucket move! All of the pilot controlled spools were stuck from sitting up. I have got all but the left track working (wasn't easy) I ran out of time and will have to work on the left rack some more. Thanks for your help.