heres the scenario , Im driving my digger today and I stop using the two joysticks that control the slew & boom functions . I instead use the two foot pedals to control the track motors & a separate hand lever that operates the blade [ not to be confused with the diggers bucket ] I finish blading off the surface, after some 5 - 10 minutes of bucking as I bladed and grabbed the two joysticks but both were completely dead ! I have no slew or boom functions . To recap, I can drive forward or backwards and I can raise and lower the blade .NB as I write this I realise something , and that something confirms the pumps are working fine .I will post below, the answer to my diggers problem , as I found on the internet . I think he is 100% correct . He finishes by saying there are two possibilitys, 1; the pressure reducing valve is faulty & or is stuck in the off position . OR 2; the accumulator is faulty . ha hah ! he tells me how to test the accumulator and yes, I was unable to lower the boom to the ground . Two more things , the auxiliary hydraulics [ tilt bucket ] worked fine it worked by an electrical circuit . He says the foot pedals and tracks are controlled by lever or cables -- manually ! whereas the joysticks rely on a lower preausre [ the spell checker said Pleasure Treasure ] low pressure to operate . Clearly I have no low pressure . But , the fact that the accumulator is empty of enough pressure to enable the boom to drop to the ground seems to me to prove its the pressure reducing valve stuck shut . Id be very surprised if anyones read this far , let alone tried to work out if bellows answer is correct [ technically ] So , is he right ? and if so , is it my valve or the accumulator ? Im guessing valve . Another part to the puzzle , re two hydraulic pumps on this machine [ a 331 bobcat excavator - feel free to google I did :) ] one pump serves certain functions & the other, separate other functions . Its just possible the the activated stems he speaks of are , in Kiwi terms , solenoids ---- so the left console is lowered and the sensor - not just a switch - energises [ puts 12volts through to the solenoid allowing that pump to preform its tasks . THe aux hyd circuit -- and by default pump -- is the same as the track motors , a fact proven when at high travel speed, the tilt will not function as the pump is working to full potential and [ theoretically ] you should not need aux hyds as you are walking fast , however at low speed the tilt function works . I say all that because should the solenoid be faulty and perhaps it is that pump that supplys the low pressure manifold that has failed to give the joystick system pressure this means both the press valve & accumulator could be fine . Its a bastard having a analytical brain at times . so the questions ; what needs doing ? take a new solenoid and replace one of the two , then if nothing changes , the other one . if nothing changes, both original solenoids are good , move to replace the low pressure regulator , nothing changes , replace accumulator . nothing changes burn machine !! Im tired thinking of it . so , one small book later , heres that expert opinion below . The left console lockout is a sensor, not just a switch, so do not try to jumper it out of the system. The 331 console lockout energizes the lockout valve stem on the pilot manifold when the operator puts the console down. This stops all pump flow from draining to tank through the lockout valve stem. Since you say the blade and travel functions work, I have to believe that the console lock out system is working correctly, or else nothing would work. Also, the gear pump indicator light should be illuminated when you lower the console, indicating the machine is operable. The blade and travels are controlled by cables and linkages, and the joystick functions are pilot pressure operated. Since only joystick pilot operated functions do not work, I think the problem is pilot pressure related. It sounds like the pressure reducing valve, which limits pump pressure down to pilot pressure of 435 psi, may be sticking closed and preventing pilot pressure from building and charging the accumulator. The accumulator may also be faulty. You can test pilot pressure with a 1000 psi gauge, on the G1 test port on the accumulator manifold, and should only have up to 435 psi when you deadhead the blade lift. Test the accumulator by raising the boom, turn off the engine, turn ignition back on but do not start engine, left console down, you should have pilot stored in the accumulator to allow you to lower the boom to the ground. Read more: justanswer/heavy-equipment/499nj-331-bobcat-mini-excavator-when-set-down-let.html#ixzz3KM8IxkTd
Posted on: Fri, 28 Nov 2014 11:13:13 +0000
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