Volvo EC25 Main Boom lowering?

[Newtoexcavators]

Hi guys and gals,
Sorry to come to the community without anything constructive to bring to the plate, but I have read a few of the threads here and think that if anyone can help it will be here. I am having a problem with my EC25, if I pull the joystick to raise the main boom it initially lowers until I pull hard enough that it stops and then if I pull it harder it will rise? I have checked the ram by disconnecting and blocking the ram with it risen above the ground and jumping up and down in the bucket but it doesn't budge. I then swapped the pressure bypass valves on the front of the spool valve to see if it was bypassing oil until the pressure applied via the joystick movement had risen to a point to force the valve shut but this had no effect whatsoever? I removed the piston in the spool valve and it looks fine (no marks or scratches at all). I looked for a check valve on the lines but there is nothing fitted. I am thinking spool valve? But before I remove the bank I was wondering if they are resealable, and if so are the reseal sets readily available? If not are the valves readily availably or is it an authorised dealer only part?
Sorry for the pretty full on first post! Any help would be greatfully apreciated. Thanks very much

[Muz]

I had one do the exact same thing, but it was years ago and I cant remember if I ever fixed it !! I think it got traded in , if I remember correctly . I have to say though, from a simple plumbing perspective, it must have to do with a drop in pressure on one side of the spool. I wouldnt be too hasty in pulling that slice out just yet though without investigating where the pressure has gone. When you open the circuit to lift, theres obviously a lack of pressure immediatly as the spool opens that allows the boom to drop momentarily, I wonder if the accumulator has any part in this ? ... Welcome BTW

[Newtoexcavators]

Wow, that was quick.
Thanks for the warm welcome.
Definitly agree with the pressure dropping and being redirected elsewhere. Going to show my ignorance now, but do the individual valves have access to the accumulator valve? Or do they have individual ones, as I have no problems with any of the other functions? Sorry, but as the name suggests, I'm new to excavators and am unsure where the accumulator valve would even be located. I suppose for most it is an old machine, being 2007, but I have just purchased it for a self build. If it were just for trenching or landscaping I would just work around it but as I will probably need it to lift lintels into place and other precision work I could do with rectifying it but don't really want to go to the dealer as can't afford it. Any suggestions that you may have regarding location and testing the valve would be gratefully received.
Cheers

[Muz]

The reason I'm wondering whether or not it plays a part in the problem is because, that is its actual function ... in so much as, when the engine is off, with the ignition on, you are supposed to be able to push the stick forward to lower the boom to the ground without flow from the pump.

[Newtoexcavators]

Thanks Muz,
Can I just clarify please that with the ignition on and the engine off I should be able to pull (to raise the boom)or push (to lower the boom) the joystick and the boom ram should lower the arm to the floor as a safety procedure?

[Muz]

Thanks Muz,
Can I just clarify please that with the ignition on and the engine off I should be able to pull (to raise the boom)or push (to lower the boom) the joystick and the boom ram should lower the arm to the floor as a safety procedure?

Yes .. push to lower it. The actual accumulator is a red coloured round spherical object beside the hydraulic tank under the RHS side cover. Its only a hunch mind

The other suspect would be something getting the spool to move the wrong way when the service is pushed/pulled on, when you had it out I take it there wasnt any broken spring inside the cap ?

[Newtoexcavators]

Thanks again Muz,
I will take a look and do some investigative work on Monday. As for the spool valve piston; it looked perfect and the caps on top of the valve were not leaking and the springs and top hats were fine. Everything looked fine? To be honest I was hoping for an obvious fault so as to have an easy fix, but no! Thanks for your help so far. I will take a look as to exactly how to test the accumulator valve and give it a go (unless you know off the top of your head and don't mind sharing?)
Thank you for your help,
Cheers