Safety interlocks not working in my Komatsu SK820.

[contractor bill]

My construction company owns a Komatsu SK820 turbo 2 speed utility skid-steer. The bucket is controlled by foot pedals. We've had the machine for about a year. Last week my operator told me about a problem he was having with the machine. While he was excavating dry dirt from a ditch and moving it about 20 feet away he noticed an operator working a backhoe fall out of his machine. My operator immediately tried to help him out. He unbuckled his seat belt, raised the arm bar and by mistake stepped on the left foot pedal. The left pedal controls the up and down movement of the bucket. Almost immediately the bucket dropped. Afterwards my operator told me that the bucket should not have dropped if all the safety devices worked on the Komatsu. I believe that there is a seat sensor and an arm bar sensor that if activated is supposed to shut the system down and even if the pedal is depressed the bucket should not move. In our case the bucket did move downward and it could have been fatal to my operator. Can anyone tell me how the safety sensors and safety interlocks work in the Komatsu? Could the machine have a faulty hydraulic or spool valve? Could the small circuit board (in back of the seat) be malfunctioning? Please help.

 

[Tazza]

First off, the operator is at fault, the correct way to operate the machne is to shut it off before exiting. This is shown in the manual and your operator should know this. With that said, we all still do it.
I don't know what type of safety devices your machine has and how it locks the operator out.
I would suspect if a sensor was not working right it would lock you out, not cause it to keep working. It wouldn't hur to to examine the switch to ensure dirt or something has not caused it to stick on making it think someone is in the seat at all times.

 

[contractor bill]

First off, the operator is at fault, the correct way to operate the machne is to shut it off before exiting. This is shown in the manual and your operator should know this. With that said, we all still do it.
I don't know what type of safety devices your machine has and how it locks the operator out.
I would suspect if a sensor was not working right it would lock you out, not cause it to keep working. It wouldn't hur to to examine the switch to ensure dirt or something has not caused it to stick on making it think someone is in the seat at all times.

Tazza, thanks for the input. We checked the seat switch and it was OK. My machine has an arm bar that when raised is supposed to lock-out the bucket arms, or prevent the bucket from moving. You are right in saying that my operator was at fault, but he was able to get out of his machine and rescue my guy on the backhoe. I'm still confused as to why raising the arm bar didn't lock-out bucket movement - even when my operator stepped on the left foot pedal!!! We're not operating the machine again until I understand what's going on with the safety interlocks. A friend of mine thought it could be a bad spool or hyraulic valve. If anyone in the forum can help me out on this problem I would appreciate the input. Thanks.

 

[Tazza]

Tazza, thanks for the input. We checked the seat switch and it was OK. My machine has an arm bar that when raised is supposed to lock-out the bucket arms, or prevent the bucket from moving. You are right in saying that my operator was at fault, but he was able to get out of his machine and rescue my guy on the backhoe. I'm still confused as to why raising the arm bar didn't lock-out bucket movement - even when my operator stepped on the left foot pedal!!! We're not operating the machine again until I understand what's going on with the safety interlocks. A friend of mine thought it could be a bad spool or hyraulic valve. If anyone in the forum can help me out on this problem I would appreciate the input. Thanks.

Sadly i don't know what they use as lock outs. On bobcats they use manual lock outs for the old machines, they went to a solenoid that blocks all fluid to the lift and tilt functions if the safety device is not detecting someone in the seat. The other uses a solenoid poerated pin that locks the spool.
The thing is, all these devices are normally closed. No power they stay locked, so if they fail they would fail closed and would lock the operator out....
If you can look under the seat, check the control block, see if you can work out what sort of lockout it has and work from there by wiggling the pedal that allowed the lift arms to move. I know that if you have leaky spool seals, the style that uses a pin to lock the spools out can get stuck because of the thickness of the oil. It could be as simple as that.

 

[skidsteer.ca]

Sadly i don't know what they use as lock outs. On bobcats they use manual lock outs for the old machines, they went to a solenoid that blocks all fluid to the lift and tilt functions if the safety device is not detecting someone in the seat. The other uses a solenoid poerated pin that locks the spool.
The thing is, all these devices are normally closed. No power they stay locked, so if they fail they would fail closed and would lock the operator out....
If you can look under the seat, check the control block, see if you can work out what sort of lockout it has and work from there by wiggling the pedal that allowed the lift arms to move. I know that if you have leaky spool seals, the style that uses a pin to lock the spools out can get stuck because of the thickness of the oil. It could be as simple as that.

Bill
Unfortunate Komatsu are not that common and I have never seen nor worked on/with one. I would call your dealer and see if you can get a manual for it. The system is likely not that complicated that you can't work on it yourself but you need a manual or a good mechanic that can look at the machine to see what is going on. Even a experienced mechanic looking at a unfamilar machine may need a manual as guidance.
The problem is likely small but it is well worth the time to sort it out.
Ken

 

[skidsteer57]

Contractor Bill: did you get an answer to this question? I have info for you if you did not get an answer. Otherwise, please let me know what you found out. The safety bar it tied to a linkage that, when the safety bar is down, puts metal in front of a proximity sensor to complete a circuit. When the bar begins to raise, the metal moves away from the proximate sensor and the triggers a lock out on the hydraulics. There is a green light on the "dash" of the safety bar that should go out when the bar is raised up approximately 30 degrees or more. See if that light is going out when you raise the bar. If not, check the proximity switch to make sure there is no metal that is near it when the bar is raised. Let me know what you found out.

 

[Bsb12000]

Bill, i am having issues with one of my komatsu skid steers, i would like to ask you a few question about what you were able to figure out on your machine. Thanks, Brent 770-893-7567

 

[bsb1200]

Contractor Bill can you please call me about an issue you had with your come out to SK8 20 skids deer back in 2011 my father was killed due to the exact same issue you had with your skid steer and I would like to get your account of what exactly happened. Thank you for your help Brett 770-893-7567

 

[bsb1200]

Contractor Bill can you please call me about an issue you had with your come out to SK8 20 skids deer back in 2011 my father was killed due to the exact same issue you had with your skid steer and I would like to get your account of what exactly happened. Thank you for your help Brett 770-893-7567

Please give me a call or email. I will gladly compensate you for your time. Brett Booher 770-893-7567 [email protected]

 

[bsb1200]

Contractor Bill, If you are out there please contact me me at 770-893-7567. My email address is [email protected]