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Pc228 no hydraulics please help!

Discussion in 'Excavators' started by powerjoke, Aug 13, 2014.

  1. jofc

    jofc Active Member

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    Second stage relief, pilot lockout, merge-divide, travel junction to name a few more,

    Have you confirmed pilot pressure? 3-4 Mpa. Pump standby pressure? 3.6 mpa. What does gauge show for hyd temp? Hot by touch is very subjective, machine can be at 60 degrees C (140 f) which would feel hot, but is normal operating temps.

    Theese machine have an unloader valve and a main releif. In neutral when destroked all oil should be flowing out unloaded valve at standby pressure.
     
    Last edited: Aug 17, 2014
  2. powerjoke

    powerjoke Senior Member

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    tell me more about the unloader and relief, where they at whats the troubleshoot etc.

    thanks for the input guys
    pj
     
  3. lantraxco

    lantraxco Senior Member

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    Wild guess, it sounds like maybe one or both pumps are actually on stroke, but the unloaders never shift so all the oil is flowing around in a circle making heat. Odd though, unless I'm missing something all the return oil from the valve stack should flow through the cooler. Any chance this machine has a fast warmup feature or option? Just rambling, sorry.
     
  4. smokey73

    smokey73 Member

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    The PC228 is a closed loop system and doesn't have an unload valve. Go back to the basics and start from the beginning: are the pumps turning? Crack a line on the pump while its running and see if oil comes out. Once you're sure the pumps are turning, check the pilot pressure. The self pressure reducing valve is a common failure on PC's. At the back of the control valve, near the top close to where the lines come in from the pump, you should see a smaller square block (approx. 4inx4in) held on with 4 allen head bolts. On the side of this block there should be a pressure tap pointing straight out the side. You should see about 30kg, this is the self-pressure reducing valve reading or basic pressure or pilot pressure, whatever you want to call it, and it feeds the solenoid bank. With out it, you've got nothing.
     
    Last edited: Aug 17, 2014
  5. rmllarue91

    rmllarue91 Senior Member

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    Hey PJ
    With this being a DOA machine should check suction stainers and return filters before trouble shooting.
    Oil starvation and contamination could be occuring during diagnosis causing effects on diagnosis and the check book. Lol good luck
     
  6. John C.

    John C. Senior Member

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    Actually this is not a closed loop system at all. It is a closed center load sensing system. There is a load sensing valve which senses pressure going out to an implement when a valve is stroked. That pressure is felt at the controls on the pump which increase flow from the pump until there is approximately 300 PSI more pressure at the pump outlet that at the implement. Older systems also have a main relief valve operated when traveling or the power up button on the left control handle in the cab is pushed. In newer systems the load sense and main relief were incorporated in one cartridge. Basically you need a book and plenty of study to understand the system.

    I have been thing about this some at times though and I wonder if the out lethoses from the pumps are hooked to the wrong valves. Get a book or schematic and follow them out. Crossed hoses would mess up load sense function.
     
  7. powerjoke

    powerjoke Senior Member

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    well that makes since why my older 228 sometimes has track power sometimes it does not the travel alarm sometimes works as well......they are probably both either working or not at the same time and i've never realized it,,,,,,, is that a poss ??

    also on that old machine the left button is jacked up and the 2speed switch doesnt work, they have bypassed the electronic throttle..... i have had it for years never got around to straightening it out.

    pj
     
  8. smokey73

    smokey73 Member

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    How is the electric throttle bypassed? Pull cable? If so, I bet it's a dog, there's no way for the engine to respond to pump load and it will bogg down.
     
  9. powerjoke

    powerjoke Senior Member

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    Ya it's got a pull cable, it's got tons of power not a dog at all
     
  10. jofc

    jofc Active Member

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    When in neutral, When the pump is at minimum angle, ie little displacement, the pump still puts out roughly 10% of capacity for cooling and standby oil. This standby oil is relieved to an unset able 36 kg/cm2 out the unloader valve. When an LS signal is sensed, it acts with the 36 kg/cm2 spring so pressure can now build in the control valve.

    If you have an LS leak, the signal can become low.
    Example;
    250 kg/cm2 needed for moving rock
    200 kg/cm2 LS signal because of major LS leak.
    36 kg/cm2 spring.

    200+36 > 250

    Pump pressure can crack that unloader valve and dump to tank rather than actuator.

    This is all really useless information if you don't have pilot pressure. The self pressure reducing valve likes to seize in these. There's a little coin filter in it that blows or plugs and sends shards into the spool. It's the thing that looks like a pack of cigarettes bolted to the control vale with 3 8mm hex bolts. Without pilot oil, your pumps won't stroke right and your joysticks are useless.
     
  11. powerjoke

    powerjoke Senior Member

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    I just went back and re read this thread after working on the machine again today and it's got me confused again lol. Any new ideas ?

    I'm affraid we might have a bad pump, I pulled the epc valves and found traces of metal, the pump closest to the motor has a lot of pressure (not sure how much I didn't have my gauges hooked up) the pump farthest away has very little psi, infact I was able to hold my thumb over the test port with engine running

    Something else I thought was really interesting is that we took the bucket off of it yesterday and the boom and stick stayed in place, I hit the key fired right up and let the boom down nice and slow but it will not even come close to picking it back up, (that means we have electronics and pilot circut operating correctly right??)

    I then took the top off the filter housing and we have absolutely NO oil getting ran back thru it there is also no traces of any trash in the catch basket on the filter.

    New thoughts ? Thank you

    Pj
     
  12. powerjoke

    powerjoke Senior Member

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    Being able to let the boom/stick down we have to have a good pressure reducing valve and pilot circuit ? If the main pump is bad why wouldn't one side of the pump at least try to operate some function ? Merge valve problem ?