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Weak stick on Komatsu PC200-8

Bermudian

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Joined
Jul 1, 2020
Messages
15
Location
Guatemala
I am working on a PC 200-8 excavator (serial # C62338) that has a very weak stick. The stick normal relief is at 150 (2130 psi) and the power relief is at 200 (2850 psi). According to my manual these figures should be 355 (5041 psi) for stick relief in economy mode and 380 (5400 psi) for power mode. Both the bucket and the arm reliefs are higher even though they are still low with normal relief at 250 (3550 psi) and power relief at 330 (4700 psi). The track reliefs are running normal at 395 (5600 psi) on both sides so the pumps have the capacity of high pressure. I am looking to up all the boom pressures but especially the stick. The main relief valves are set at 5600 psi so they are not causing a problem and we have swapped the valve block relief valves around and that has not helped. Is there a relief valve that I am missing? Why is the stick so much lower than everything else? We have tried to set all the pump pressures according to the manual and the functions operate at normal speed but lack power. Any ideas will be appreciated!
 

John C.

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Jun 11, 2007
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That machine is a closed center load sensing system. The main reliefs are set above the pump destroke and only as a safety. The circuit reliefs also work the same way. Your issue sounds to me like the load sense for the stick is not being picked up at the pump. Check the pressure on the stick while running the boom up over relief at the same time and see what happens. If stick pressure remains the same; you could have a problem in the cylinder, there could be a problem in the compensator valve for the stick, for some reason load sense pressure is not getting sent to the pump. Have you checked the monitor panel for any codes? Are you checking pressures from the monitor panel?
 

LACHAU

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Aug 11, 2009
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Saigon, Vietnam
Have you checked the monitor panel for any codes? Are you checking pressures from the monitor panel?

b0212.gif


KOMATSU excavator dash 8 allows you to check various parameters on the screen.
SO MANY PARAMETERS you can check in SERVICE MODE.

K1.png


K2.png
 
Last edited:

Bermudian

Member
Joined
Jul 1, 2020
Messages
15
Location
Guatemala
Thanks for the info. There are no codes on the machine. I am giving the pressures that the monitor panel gives but we have put pressure gauges on the system and they read the same as the monitor. We have manually checked pressures on everything we can think of and even had one of the pumps apart. When we had the machine on the lot, we got a much higher pressure rating when we relieved the stick and the bucket together but after running it hard for several hours that no longer made any difference.
 

Bermudian

Member
Joined
Jul 1, 2020
Messages
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Location
Guatemala
More directly at your questions John C. No codes at all. I just swapped the compensation valves out for others and it makes no difference. When I move the bucket or boom at the same time as the stick, the speed and pressure increase greatly. I do not have to run bucket or boom against relief to get this result. According to control panel the PPC pressure is at 35 (500 psi) on all 3 functions. We just rebuilt the stick cylinder so that rules out a faulty cylinder I assume. Any other ideas why the pump is not being fully activated by the stick cylinder?
 

John C.

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What is the pressure on both pumps when you stall out the boom and the stick at the same time?
 

John C.

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Does the stick pick up power when you operate the boom slowly as you are pulling in the stick?
 

funwithfuel

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Mar 7, 2017
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Location
Will county Illinois
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There is an additional relief for boom n arm. It's common to boom and arm. Is your bucket circuit strong? This is for sure on -10 &11 . I will check if it's on -8 as well.
 

funwithfuel

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Will county Illinois
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The valves are integrated in later production but in the -8 they are separate. Boom and arm drift prevention valves. On front side of valve towards bottom left as you're looking at it.
Item 8 & 9 in pic.
 

Jgm

Well-Known Member
Joined
Jan 30, 2019
Messages
125
Location
Germany
Just like funwithfuel explained, when all pressures are good, 90% it's the additional valve which are on your block. Just to give you a tip, your pressures could be set higher, power max at 405 bars, secondary at 390 and main at 380. I use those pressures on our maschines starting from PC 138 and up and on PW 148 and up, no problem and customer happy.
 

Bermudian

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Joined
Jul 1, 2020
Messages
15
Location
Guatemala
Yes, John C. the stick moves considerably faster when the boom is slowly raised. Also for the other replies, my bucket and boom circuits are much stronger running at 240 (3400psi) whereas the stick doesn't put out more than 150 (2130 psi) on economy mode.I know the other functions are still low and I would like to up them as well... Another thing I notice is the swing is slow but speeds up considerably when the boom is raised. Is there a link between the two?
 

Jgm

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Jan 30, 2019
Messages
125
Location
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Yes this is normal, your boom up will help compensate the swing pressure, to help with your cycle times.
 
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