Komatsu PW140-7 hydraulic load issues

[Johnny English]

Hi Guys, we have a PW140-7 rubber duck. We put a rotating selector grab on it the other day from a local hire place. Several days later we stopped the machine and it wouldn't start again. Starter checked out fine and still no joy. Eventually had to call out komatsu, he looked at hydraulic pressures and the system was at over 300 bar when cranking over rather than 11 bar.

He took the LS line off the hydraulic pump and it struck up straight away. Turns out the pump was under load before the engine had chance to fire. Problem is they don't know where the signal is coming from to the pump down the LS line. The next phase is to take the pump off to be checked, they think the swash plate may be stuck in the pump. Failing that we have to start checking out the valve block for a sticking valve etc.

Has anyone had any other such problems or suggestions.

Many thanks

 

[Per Eriksson]

I wouldn't start with the pump because if everything works ok in the valvebank there wouldn't be any LSsignal coming to the pump even if it is at maximum strokesetting.

You could put a ball valve in the ls line so you can start it again and then open the valve and test all the functions to see if you can find anything that is acting weird, most likely a compensator/ls signal creating spool is stuck or has a broken spring.

But I bet the pump isn't to blame.

 

[Johnny English]

Thanks for the reply.

We're in the hands of the Komatsu team at the minute, our local independant fitter didn't know where to start so we had to call in the big boys. The pump will be whipped off and checked over on a test bench at a local hydrauilc specialist, at least then it can be ruled out as ok then we can carry on from there (hope the pump isn't shot, we've been warned one could be £10,000 plus). I'll mention the ball valve idea to the fitter. Thanks for the input.

As it happens our machine set off its life in Sweden, we bought it last year with 600 hours on it as an import from Sweden, its been a cracking machine so far, hopefully have it recified soon.

 

[John C.]

I used to see that problem all the time on the PC120-6 gray market machines that came in to the US. Per is most likely correct in his diagnosis because that is what I found on these machines. There was a small spool behind the swing control as I recall. I was clued into it from a friend at the local dealer. I don't have the part number anymore but used to carry a spare in the truck all the time. The spool would actually spin in the bore and turn black on one end and then stick. That let load sense pressure go to the main pump and put the swash plate at full stroke as soon and the engine started turning over. I check to see if the problem only happens when the machine is a operating temperature. Maybe once it cools down the problem the problem goes away until the system warms up?

You might ask your dealer about it. This may not be exactly the same problem you are having but it will be something similar. It is possible that contamination was introduced into the system and is holding a spool the wrong way or a proportional valve open.

 

[michel]

Johnnny, there is LS load and you are at relief pressure 300 bar and cranking is difficult, which means a spool in the main control valve is actuated. And if a spool is actuated an actuator should move so if no actuator is moving it should be the service valve you are using for the attacment that is actuated intentionaly

 

[Per Eriksson]

I would question them on removing and testing the pump as a first action, the pump has already been cleared when the ls line was removed and it didn't build pressure then, waste of time and money(your's)

 

[Johnny English]

Spoke to Komatsu again today before they take the pump off tomorrow. They tell me that when they have taken the LS line off, it has only dropped the pressure in the pump enough for it to start. The pressure is still high when starting but just low enough for it to crank up. With the LS line off, when you stop the engine its stops very abruptly. They think the swash plate is stuck 3/4 open. They claim that if the LS line is removed the pump should operate only at a very low percentage of its full capacity and it is well up on that without the LS line (the machine travels and operates reasonably well still with the LS line off, when it should be very low on power) this is what makes them think the pump is stuck on 3/4 power. But this still doesn't explain why the LS line needs to be removed, something was still telling the pump it needed full power when it shouldn't, so a spool must still be stuck open even if the pump is faulty. Should find something out by the end of tomorrow.

The big problem is I don't understand enough about the hydraulic system to poke my ore in too much, we just have to put our faith in the professionals and pray

Thanks Guys, I'll keep you posted

 

[willie59]

Johnny English, I'm no expert on Komatsu LS system that you are referring to, but it's possible the LS line is supposed to have a certain amount of pressure on it when no functions are being operated. This causes what is known as "standby pressure" on hydrostat pump systems. I'm not saying for certain that's the way this system works, only saying it's possible all things are correct on the LS system and the fault is, in fact, in the pump.

 

[SFOSTER89]

The swash plate spring might of snapped and may not be allowing the swash plate to return to minimum flow. Then when the LS pressure is fed to the pump on start up, just like you say, this may be pushing the swash plate from half way upto 3/4 of max flow. Which will drag your engine down under starting, or like your problem not allow your engine to start at all.

 

[vinpetrol]

Hi Johnny

Did you ever resolve this problem with your hydraulics ? I have a pw140 -7 and have a similar issue . Mine will not start after hydraulics have run hotter than normal when I drive long distances down hill untill I let it cool down .

Vin

 

[islander47]

I ! I’ve got one nearby with same issue. I believe it comes from some wear in the pump. Can be rebuilt. Something like the rocker got stuck and so the variable stroke of the pump doesn’t destroke when starting. When starting the pressure rise and as the volume of oil produced is not used , the pump have to destroke immediately itself. If it doesn’t because don’t slide well, then the pressure rise up to 350 bars but it pull too much on motor so it just can’t start.