Kobelco SK330 Boom drops

[mkoepf]

I have an issue with the boom dropping once the joystick is released. Its an SK330-6 pre m/c machine with 8400 hours. The pumps were replaced around 4700 hours. I put gauges on and pressures are all in spec. Were doing some heavy lifting just shy of 18,000 lbs. According to the chart on the machine this is right at the limit for our dimensions we're lifting from. The boom will not lift this by itself, but the arm will pick the load up but as soon as the load starts to raise the boom falls, even if I'm still holding back on the joystick. The cylinders are not warming up as if they were internally leaking. I've inspected the spool inside the boom lock selector valve, the boom spool itself, checked out the check valve in the boom conflux citcuit, and swapped circuit reliefs with one of equal pressure setting and made no difference. I've been pulling my hair out over this issue for a couple weeks. Hope someone can point me in the right direction.

 

[Chris5500]

Given the circumstances I wont give you a step-by-step on what to do, how to do it or what order because it sounds like you have a fair idea, and given the nature of what you are doing it sounds pretty straight forward to me what is happening.

The fact that you have checked the pressures and they are all in spec (assuming you checked the secondary's) and given the nature of the task you are doing, leads me to believe that you are overloading the machine (regardless of the chart saying otherwise), the service line relief valves (secondary's/SRV's whatever you prefer) are opening under the pressure to limit the maximum possible pressure peak in the service line (which is what they are designed to do).

 

[MR. KOBELCO]

if you lift a lighter load does the boom hold the load or does it drop?
also how far are you lifting out away from the machine?
over the side or over the front?
are you lifting with the bucket on or are you able to drop the bucket?
ground level, above or below?
how is the load chained?
sometimes you need the machine planted higher than your load lifting to compensate with the physics behind the lift.

 

[MR. KOBELCO]

you say you checked the pressures?
what were your results?
did you access the machines maintenance sreens?
before checking pressures all the sensors, e/g rpm sensor, hyd pressure sensors all must be reading proper.
i can help confirm.
call me when you are in your cab and i'll talk you thru it.
905-888-9070
ask for me.
adam.

 

[mkoepf]

I recorded pressures first right around 4900 psi. Now I have adjusted the main relief to 5200 psi regular and 5400 psi heavy lift. I have accessed the maintenance screens and recorded the info but nothing jumped out at me that seemed out of place. I removed, cleaned, and readjusted the rpm sensor and compared the dash to an external tach.

As far as the lifting, I would say I'm approximately 20 feet in front from center of the machine. I am lifting from the bale on the coupler, with no bucket. I'm lifting concrete barriers from ground level, but with the stick all the way out it's probably around 10-12 feet above ground.

I also have a special tool on the way that blocks off the cirtcuit relief to check that I'm not having any fluid escaping there.

 

[MR. KOBELCO]

YOUR MACHINE MAY OR MAY NOT HAVE HIDDEN SCREENS WHICH NEED TO BE RESET PRIOR TO BELOW SEQUENCED EVENTS.
BEFORE ADJUSTING HYD PRESSURES THE E/G RPM's MUST BE IN SPEC.
YOU MAY NEED TO DO WHATS CALLED AN "A" ADJUSTMENT.
I CAN LEAD YOU OVER THE PHONE OR E-MAIL YOU THE PROCEDURE.
IMPORTANT TO READ FULLY AND HAVE A GOOD UNDERSTANDING PRIOR TO FOLLOWING STEP BY STEP.
THE ENGINE RPM SENSOR IS ADJUSTED AT LOW IDLE & READ 9 - 11 VAC @ LOW IDLE.
THE KOBELCO TECH INFO ON RPM SENSOR IS USUALLY INCORRECT IN THE TECH MANUALS.
ALL HYD PRS ARE READ AND/OR ADJ IN " H " MODE AT FULL E/G RPM.
THE SMALL GEAR PUMP (PILOT PUMP) IS SET @ 780 PSI.
WITH HEAVY LIFT ROCKER SWITCH ON THE LARGER LOCKING NUT LOOSEN AND USING A WRENCH ADJUST UNDER BOOM RAISE OVER RELIEF TO 5650 PSI.
THEN TURN OFF HL SWITCH AND LOOSEN NUT AND USING ALLEN KEY ADJUST MAIN RELIEF UNDER BOOM RAISE TO 5050 PSI.
THE SWING RELIEFS ADJUST AS "H" MODE FULL E/G RPM BUCKET TEETH LOCKED IN GROUND AND ADJUST TO 4700 - 4800 PSI.
ONCE ABOVE DONE AND VERIFIED THE E/G STALL RPM LIKELY WILL HAVE TO BE TWEAKED TO GET THE MOST FROM THE MACHINE.
ADAM.

 

[mkoepf]

The RPM's are 996 at low idle and 2384 at full throttle. I just put an A adjustment into the machine a week ago. The RPM sensor is at 9 VAC at low idle. Pilot pressures are at 780 psi at the pump. My pump pressure with heavy lift off is about 5200 psi and with heavy lift on about 5400 psi.

I recieved my circuit relief tool today and installed that in the boom up circuit relief and tested the machine out. The boom has no problem lifting now and holds as it should. This points me in the direction of this circuit relief. Since I swapped the boom up circuit relief with the bucket dig circuit relief and made no difference in preformance I'm thinking that maybe the seat for the relief is marred or otherwise allowing oil to escape.

 

[mkoepf]

I aquired a tool from Kobelco and cut a new seat in the boom circuit relief. Everything functions as it should now.

 

[Chris5500]

I don't suppose you have any photos of the condition of the old seat, the new seat, what you did to cut the seat and the tool itself? Just curious

 

[cps]

I don't suppose you have any photos of the condition of the old seat, the new seat, what you did to cut the seat and the tool itself? Just curious

I would Also like more info on this procedure, and any pictures (even just of the tool used)

Sounds like an expensive repair.... just curious also

 

[mkoepf]

I don't have any of the seat itself, just the tool. And they were taken with a phone so there not real clear. Let me know if they don't show.

The tool has a guide that screws into the port for the circuit relief. Then the cutter rides inside the guide. It has a diamond cutter head. Basically what this procedure does is just clean up the seat. Push down on the cutter with your hand while turning with a wrench. If there was a serious gouch or something in the seat i don't believe this would work. I'm not sure how much you can take off.

The dummy relief circuit looked just like the relief only no holes. Thats how we narrowed the problem down. Spent many hours troubleshooting.

 

[mkoepf]

this is the part that cuts

 

[Chris5500]

Thanks for the photos and explanation, quite interesting really. I've never seen or heard of this tool and procedure before, could it be that Kobelco have casting issues with their control valves accross the range and experience fretting of the seats of their relief valves and have produced this tool as a result?

Anyway, in your case (since reconditioning the seat fixed the problem) the secondary relief valve seat was blemished in some way, which, depending on the type of relief valve used and which seat was damaged (which judging by the pictures of the tool I would say the main valve cone seat) would lead one to believe that it was bypassing service pressure directly and not pilot balance pressure within the valve itself (even if it was pilot balance pressure bypassing it would still cause the same problem)

I’ve seen a similar problem a handful of times before where it was bypassing the main valve cone seat, not from being blemished, but from being insufficiently tensioned (more often than not they are over tensioned to “F.T.” Newton metres with a 12ft pipe on the end of a spanner). The machines I’m used to (Komatsu’s KMG range of excavators) require all relief valves’ (MRV, SRV and PIRV) to be tensioned to 300Nm; otherwise the internal sealing properties are not true which result in setting difficulty, loud flow noises and abnormal temperatures.

I’m not having a go at you but the point I’m trying to make is how you could only pin point it by using the dummy relief valve, I find it hard to believe that the pressure was still in spec (and no mention of any noise or over heating problems) yet the boom was self acting once the control lever was in neutral. Surely if the SRV was bypassing through the main valve cone seat then it would not be able to maintain the set pressure and would subsequently show on the pressure gauge upon stalling the system?

:beatsme

 

[MR. KOBELCO]

just a thought, the dummy relief screws into the port seating itself unto the same seats the actual overload port relief does.
the boom lifted for your circuit was running on the main relief now plus it did not fall for once you stop movement and spool centers the oil has no place to go now.
therfore, the seats in the main hyd control valve are okay.
the problem is likely with the overload reliefs. or the loads are too great.
the only time we ran into a bad seat in a c/v was when one of our customers thought that the hyd return filters never had to be changed.
they do every 500 hours along with the regular engine service.
the hyd oil gets changed every 2000-2500 hours of use.
by the way on the port reliefs usually one full turn equates to approx. 2900 psi.

 

[Chris5500]

I recorded pressures first right around 4900 psi. Now I have adjusted the main relief to 5200 psi regular and 5400 psi heavy lift. I have accessed the maintenance screens and recorded the info but nothing jumped out at me that seemed out of place. I removed, cleaned, and readjusted the rpm sensor and compared the dash to an external tach.

I guess the reason you didnt pick up the bypassing secondary (without using the dummy relief) was because (reading the above) you only tested and adjusted the main relief pressure, to check the secondary's you have to wind the mains in so the pressure is higher than the secondary's, and bearing in mind, since the the piston side of the cylinder is (usually) protected by 2 secondary's you will get the pressure of the lowest setting.

Confirm/deny mkoepf? :tong

So I answered my own question from 2 posts above, problem solved! :drinkup

 

[mrexfix]

I guess the reason you didnt pick up the bypassing secondary (without using the dummy relief) was because (reading the above) you only tested and adjusted the main relief pressure, to check the secondary's you have to wind the mains in so the pressure is higher than the secondary's, and bearing in mind, since the the piston side of the cylinder is (usually) protected by 2 secondary's you will get the pressure of the lowest setting.

Confirm/deny mkoepf? :tong

So I answered my own question from 2 posts above, problem solved! :drinkup

i think i seen same here in aust land problem very time consuming
i have worked with many kobelco over here my thery on this problem is the robot or CNC machine got out of wack there for the tool they sent u recut the corect angel that the CNC failed to do at your expence

cheers gotta go kangaroo is hungry needs to be feed

 

[mrexfix]

Thanks for the photos and explanation, quite interesting really. I've never seen or heard of this tool and procedure before, could it be that Kobelco have casting issues with their control valves accross the range and experience fretting of the seats of their relief valves and have produced this tool as a result?

Anyway, in your case (since reconditioning the seat fixed the problem) the secondary relief valve seat was blemished in some way, which, depending on the type of relief valve used and which seat was damaged (which judging by the pictures of the tool I would say the main valve cone seat) would lead one to believe that it was bypassing service pressure directly and not pilot balance pressure within the valve itself (even if it was pilot balance pressure bypassing it would still cause the same problem)

I’ve seen a similar problem a handful of times before where it was bypassing the main valve cone seat, not from being blemished, but from being insufficiently tensioned (more often than not they are over tensioned to “F.T.” Newton metres with a 12ft pipe on the end of a spanner). The machines I’m used to (Komatsu’s KMG range of excavators) require all relief valves’ (MRV, SRV and PIRV) to be tensioned to 300Nm; otherwise the internal sealing properties are not true which result in setting difficulty, loud flow noises and abnormal temperatures.

I’m not having a go at you but the point I’m trying to make is how you could only pin point it by using the dummy relief valve, I find it hard to believe that the pressure was still in spec (and no mention of any noise or over heating problems) yet the boom was self acting once the control lever was in neutral. Surely if the SRV was bypassing through the main valve cone seat then it would not be able to maintain the set pressure and would subsequently show on the pressure gauge upon stalling the system?

:beatsme

same same i thought test tool was to ilianate problem not to test preasure ???

 

[mrexfix]

Thanks for the photos and explanation, quite interesting really. I've never seen or heard of this tool and procedure before, could it be that Kobelco have casting issues with their control valves accross the range and experience fretting of the seats of their relief valves and have produced this tool as a result?

Anyway, in your case (since reconditioning the seat fixed the problem) the secondary relief valve seat was blemished in some way, which, depending on the type of relief valve used and which seat was damaged (which judging by the pictures of the tool I would say the main valve cone seat) would lead one to believe that it was bypassing service pressure directly and not pilot balance pressure within the valve itself (even if it was pilot balance pressure bypassing it would still cause the same problem)

I’ve seen a similar problem a handful of times before where it was bypassing the main valve cone seat, not from being blemished, but from being insufficiently tensioned (more often than not they are over tensioned to “F.T.” Newton metres with a 12ft pipe on the end of a spanner). The machines I’m used to (Komatsu’s KMG range of excavators) require all relief valves’ (MRV, SRV and PIRV) to be tensioned to 300Nm; otherwise the internal sealing properties are not true which result in setting difficulty, loud flow noises and abnormal temperatures.

I’m not having a go at you but the point I’m trying to make is how you could only pin point it by using the dummy relief valve, I find it hard to believe that the pressure was still in spec (and no mention of any noise or over heating problems) yet the boom was self acting once the control lever was in neutral. Surely if the SRV was bypassing through the main valve cone seat then it would not be able to maintain the set pressure and would subsequently show on the pressure gauge upon stalling the system?

:beatsme

same same i thought test tool was to ilianate problem not to test preasure ???

 

[mkoepf]

The dummy relief just blocks off a circuit relief. The main relief was opporating fine. With many hours of troubleshooting we narrowed it down to the boom circuit specifically. Main relief issues should have showed up on other circuits as well. So all it left us was the cylinders or the valve circuit. So yes, Mr Kobelco, that tool just showed me that oil was leaking through the boom circuit relief. This machine is serviced as it should be, the operator is very religious about that, but it also has high hours. Thanks for the spec on adjusting circuit reliefs!
Chris - I can guess that the flaw in the circuit relief seat was not so bad that oil could constantly pass through but just once it hit a high pressure. Holding the joystick back would push oil over main relief but when I'd let go of the joystick the pressure of the load forced the oil through the leaking seat. And I never messed with the setting of the circuit relief, just the main.

 

[mkoepf]

i think i seen same here in aust land problem very time consuming
i have worked with many kobelco over here my thery on this problem is the robot or CNC machine got out of wack there for the tool they sent u recut the corect angel that the CNC failed to do at your expence

cheers gotta go kangaroo is hungry needs to be feed

This machine had over 8000 hours on it.