Hi guys, I have a Komatsu PC200-7 with a damaged spool in the control valve for the bucket line. Because of this the bucket cylinder drifts in both directions. I have checked lots of shops to fix it but of no use plus it will cost me a fortune. I was thinking of installing pilot operated safety check valve in the bucket line to lock the pressure. Any expert opinion will it work? If yes then how can I install it. Thanks
Dual counterbalance valve is what you need for a start.....
Yep that too. I need somebody to explain how to install it.
What makes you think the spool is bad. The bucket should be holding on the lift checks when the spool is centered. My guess is the cylinder or the compensator is leaking by.
Does Kommie use lock checks or just load checks like everybody else? Load checks just hold the load from dropping as the spool leaves center, until the pressure can build to the point of moving the load.
Its because I have done a reseal for the cylinder twice and replaced the compensators. Actually some time ago this particular spool got jammed inside the control valve because of debris, so we had to pull it out by force. We had the whole control pulled out to reseal it and noticed a deep scratch on the seat where the spool is to sit. We had to polish the spool a little bit to let it move freely. Since then its leaking internally causing the cylinder drift. Im looking for a quick and cheap fix because the agency is saying I have to buy the whole control which will cost me a fortune. Thanks
This is how my control valve looks like.
You can have the bore honed and the spool plated and ground
If that is too expensive, how much do you think holding valves for that size and pressure are going to cost?
I think I can find good used ones for 1500$ max.
On the other hand bore hone is possible but never heard of anybody who does spool plating here. Only honing would cost 2500$.
http://www.nagycylinder.com . Try Nagy cylinder rebuilding in Lumby, they are reasonably priced and can do about anything.
OK now I known why you are asking and I think you have done the troubleshooting well. The only other possible leaker would be a circuit relief cartridge. I have seen the bores cut over size and a new spool made but that is expensive also, probably not new valve block expensive.
Hey John can you please expain this circuit relief catridge more? Thanks
I put counterbalance valves on the cylinders on my tilt bucket. I noticed that after tilting back and forth multiple times to test everything after install that my cylinders were warm. I wonder if valves of that size would create a lot of heat and cause problems? Just a thought.
Good thought. What you suggest shimmy1? If you had this problem what would you do?
One of those deals where it needs to be fixed, and that in turn is going to take $$$. It sucks, but a -7 should be worth enough to justify fixing, I would have to believe, unless it has 20,000 hours, and even then the condition of the machine would come into play. How much are we talking to fix? $10k? $15k? Have you checked any salvage yards?
The machine has 25000 hours on it. Yeah i've checked some yards for used. The quotation came around $6000. New is around $18000.
Yup. Need to consult a *good* hydraulic man and select a proper ratio for the counterbalance valves, higher ratios mean less heat, but less stability. Also should have a tank drain since in this case you're working with a cylinder spool in the control valve.
There are circuit relief cartridges for all the cylinder type functions. The bucket function would be items 5 and 8 in the page.
Does it drift both side or just one side?
Both sides
Try to repair the control valve or find out a used one in good condition