hello men , working with my excavator this summer and I have a few questions. At my main hydraulic valve I have a pipe going to the retract side of dipper stick and a pipe to the extend side. Each have a test port which I can attach my test gauges to. I run my machine at speed and extend out. Rod side gauge pressure goes to about 3000 psi till end of stroke, then relief at 4000 psi. Other gauge on piston side goes to 0 psi while doing this. Now the other way. I retract the dipper and the piston side goes to 3000psi,and the rod side goes to 3000psi . It will stay that way with fluctuation until relief at 4000psi. Shouldn't the rod side go to 0psi also? Opposite side should be return to tank? Bucket pressures seem fine. The machine is a 4300c link belt . Another problem is when letting go of the control lever for the dipper, it is very harsh and sudden not like the boom ,bucket, and swing which are smooth. Also, my book shows my unloading valve pressure to be at 2750 psi . What procedure do I do to get this ? I have not had 1 pound of pressure ever show on this test port. My books show how to test pumps and relief pressure, bucket ,boom ,stick,pilot,but not unload. Any thoughts?
Good day If you could post the hydraulic schematic that would be a great help. Kind regards Uffex
You don't say what machine, closed center, or open center. In those valves I've seen the spool opens to alow the non pressured end of a cylinder to return back to the tank. For some reason it isn't easily being moved. Check pressure between valve & tank. I'd guess plugged filter, wrong valve, incorrect plumbing.
I can't help on the unloading valve pressure. The dipper pressure doesn't surprise me. Are these measurements with the dipper in the air? have you measured hyd pressure digging? Does it seem to have normal power digging with the dipper? "protection" valves in the dipper CYLINDER extend are common even on much smaller machines, they don't want the dipper falling by gravity so provide backpressure to keep it full of oil and moving controlably.
Sounds like arm regeneration on dipper retract to me, oil from the rod end is fed at pressure to the other end to aid in digging power, maybe there is a faulty valve on the regeneration circuit allowing pressure to build on dipper retraction instead of allowing it to flow into the cylinder normally.
As I recall there is a throttling check valve in one side of the dipper to prevent a free fall when pulling the stick in with a bucket full of dirt. I don't recall if it was in the main control valve or installed in a steel line outside of the main control valve.
Thanks for the reply, guys. Here is a hydraulic schematic, uffex. I am limited in reading hydraulic blueprints. Is there a valve in my main hydraulic control valve that softens the control motion? Is that the valve that is between the pipes at the dipper spool? It is still very harsh when I let off of the dipper joystick. It shows good power except on dipper in function. Boom up lifts fast and strong. Swing is good. Bucket is good. I can bury a 54" bucket into the ground and curl it right out. I can lift with boom with full bucket. I have 20 pounds of fuel pressure. I have 10 pounds of boost. It will push out black smoke when using dipper at stall. It's weird that with all the functions working and going into relief that the dipper will still stall the motor when retracting the dipper stick. That is when I see pressure on each side of the spool. The dipper has very little power. I have pulled out both spools in the main control valve and the other control valve. They both move smoothly and all springs are in tact and not broken. Each of the negative control lines drop to zero pressure when dipper stick joystick is operated.
Good day I have take a look at the schematic and cleaned up the relevant areas regarding your questions, if I interpret your results correctly the machine arm main hydraulics are OK but you have an issue with the control this may be as simple as blocked case drain filter so I would suggest you check this out first. Please come back if I can help out some more. Kind regards Uffex
Good day I attached some information that may help resolve the issue, please pay aprticular attention to the spool retaining spring guide, steps worn into this part can result in control issues. Kind regards Uffex
There are two spools feeding the arm circuit. If you look at the arm 1 spool you will see that it only allows for oil to go one way and there is a check valve in the spool. Basically the arm can be fed by two pumps under certain situations. If it were me, I would be pulling the arm 1 spool out to inspect first for free travel and then to make sure that there isn't something stuck in that check valve. If those are clear, you can follow the schematic on that control section at the top to see where the oil comes from and get a sense of what the control situations are.
Good day John As I have read the schematic the primary spool has only a restriction I to have seen the check valve type but the schematic in the thread appears deviod of that component or have I missed a detail? Kind regards Uffex
I have circled the offending valve spools. Arm one has the restrictor. Arm 2 has none. Also note that I have circled the control spool on the top of Arm one. Follow the piping to the sources and see if you can figure out the control scenarios.
thank you all for the quick response. When i got this machine up and running it had this issue from the beginning. i have went thru fuel system and have good supply, but the dipper has been my issue . I began to think my main control valve spool could be bypassing because of the pressure issue and some things the previous owner had done; so i changed out main control valve with a replacement. it still had same problem. This tells me issue is not in main. I will focus on checks since they are outside of valve. I will take a look at remote valve pressures going to and out of joystick to main valve and secondary valve to see if they are at pilot pressure. This didnt cross my mind , thanks uffex. I removed secondary control valve spool last summer ,it moved freely and no broken components. I will get back on it this weekend, thanks guys!
Hello men. I have been tracing hydraulic lines and pilot lines on my machine and I have noticed on my hydraulic schematic ,which is shown on this thread, the pilot lines feeding the arm in line seems to be connected to the spare valve which is right beside it in the valve bank. Also on the opposite end of the spool, the spare valve line , it is connected to the arm out line,which has the pilot supply and hydraulic solenoid and unloader valve . My question is , what relationship does the spare valve have with the arm functions. Also the spare valve is fixed so it doesnt move and both ends plugged. I understand output lines are capped , and spool movement would cause fluid under pressure to come out. does something else happen in the spare spool that could cause blockage at the dipper in spool?
Good day RatMH Forgive me for saying I believe we are in danger of loosing the original thread could we repeat what the issue is with the machine - smoking at dipper arm stall is not so unusual as machine become more worn - a common mistake often made when checking out an excavator is that the dipper arm will not power in when laid flat on the ground in spite of having full pressure - this will also be the case with a brand new machine, the geometry works against the arm reducing the force. Sorry if I am telling you something that you know. Kind regards Uffex
thanks Uffex for the response. My 4300c linbelt still has a low power situation at the dipper in function. It is almost like a deadhead problem or reduced flow issue.Went through fuel issues and everything works well except dipper in. I am still puzzled on the unloader valve function since i have never had any pressure , and book shows 2700 psi but no information on how to achive this,does this have something with my problem? thats why i asked about the spare spool question schematic shows lines to spare valve tied directly to arm in line ,but my spare spool pilot lines are plugged. my arm spools slide smooth and no damage to springs,I am just still looking for arm in blockage or issues, thanks
Good day RmH If I am interpreting the symptom correctly the arm in has little or no pressure yet the engine loads ? - the flow can be established by measuring the arm speed, im not to sure which is the "unloader" valve you refer. If the issue is isolated to that of the arm we can almost eliminate any pump problem - the arm circuit comprise of two main valves that of the primary = single pump feed and that of the secondary which adds the additional pump note this only connects with arm in cylinder out. Could tis be a simple as cylinder seals, does the arm creep in or out ? Kind regards uffex
Here is a simplified version of the CII hydraulic schematic. I am unaware of any unloader function in the arm circuit. There is two pump flow for arm out and single pump flow for arm in. The other odd part is that my schematic shows single pump return for arm out and arm in. The low pressure on the arm in circuit indicate a problem in the circuit relief or an internal leak within the main control valve. I haven't seen these valve break internally in my time working on them but with the age and probable operating time on your machine it is a possibility. When you bring the arm in, do you hear any hissing sounds on the main valve body. I've used a big screw driver at time to locate where the sound is coming from. Maybe studying this schematic might provide clues that I'm not seeing.