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Valmet 646 Hyd issue

Started by leeroyjd, April 18, 2021, 11:14:50 PM

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leeroyjd

starts and idles fine.Pump main pressure good, pilot low by 20psi.
Using any function will cause the engine to labor as if you are dead heading one. This happened suddenly while coming out of the woods.
The only thing that seems to relieve the high pressure is to switch the "float" which I Believe is unique to the 640 series that have the crane on the front half of the machines.
Normally I'd check the primary shuttles but wanted some other ideas.
The float should only effect the slew/swing, grapple rotate, and main boom, but will stop this high pressure that happens with blade and steering now which it should not.
The restriction gauge on the hyd filter is showing some restriction and I will be replacing that. 
One of the electric solenoids on the valve bank looks like oil has leaked internally, could this cause a short off some kind?
Any suggestions would be appreciated.

Gary_C

Most likely you have a problem with the pilot pressure valve. What I believe is happening is the full main hydraulic pressure is getting past the pilot pressure reducing valve and causing all your auxiliary valve functions to actuate. You need to repair/replace the pilot pressure valve and carefully set the auxiliary or pilot valve pressure. Note you have to set that pilot pressure when any of the main valves are actuated so that the hydraulic system goes to full pressure. 

Hopefully you have a hydraulic manual for that machine because you have to set hydraulic pressures in sequence starting with the main hydraulic pressure. 
Never take life seriously. Nobody gets out alive anyway.

snowstorm

Pilot pressure is not adjustable. I will look in my book but 120 psi is close. The blade is not pilot operated it has a cable.putting the crane in float affects the boom lift and swing. More than likely the o rings on a shuttle valve have gone missing. Only use the o rings from komatsu. They have improved them several times

Gary_C

I am not really sure about the hydraulics on the 646 machines as it's been  a while since I had one. I know more about the 840 hydraulics and I think it is an updated version of your machine. I had a 2+ year problem on my 840 with multiple valves actuating and it was a problem with the pilot pressure reducing valve bypassing too much pressure to the pilot system. What happened on my 840 is all the functions on the auxiliary valve block were actuating anytime one of the main hydraulic systems were actuated and the main pressure went to full pressure. After spending thousands of dollars repairing the two speed gearbox, the rear bogie axle and the brakes it was fixed by replacing a $50 pilot pressure reducing valve.

But on your machine it sounds like you are triggering the main pump to go to full pressure and it will not go back to the standby pressure setting. It would be like extending a cylinder to full extension and holding it there. If it comes on while driving it may be the steering circuit that is triggering the high pressure from the pump. 
Never take life seriously. Nobody gets out alive anyway.

snowstorm

Well did you find missing O rings ?..?

leeroyjd

Quote from: snowstorm on May 05, 2021, 06:37:52 PM
Well did you find missing O rings ?..?
Rain has kept me from taking those shuttles out.
orings will be ordered. I'm glad you say they've been improved.
Tech at Rolland wants me to swap float cartridge valve with two speed cartridge valve on the auxiliary valve under cab.
I've since discovered no extension on jib, and no grapple open/close.
Going to try to find loose or chaffed wire starting in joystick. Fuses are good.

logging pete

Outside the cab below the rear window, next to the valve bank is a two prong connector in the harness, I have had them come apart. They are round, rubber look to them.
 Roll the rubber boot up that is below joystick handle. common for the  wires to break there. The wires are short, I add enough wire to go 360` around the base of the stick, then up the handle. The thumb switch can fail also. Most of the time if it's in the joystick, you lose one side of the spool first. As in, the bucket closes but will not open. The connector outside will cause you to loose the  complete function.         You can check for a bad solenoid on the auxiliary block with a screwdriver, you will feel the magnet.  If you need one, for a test, take it off the two speed.   You can get by with out the two speed, switch the hoses and it will stay in low.  If your park brake is out of adjustment the engine will pull done suddenly when driving, if the solenoid is starting to fail. Most times you will smell the brake soon if it is adjusted correctly. That is the moment I steal the solenoid off the two speed.

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