I have a 52-6FGCU30 forklift that has intermittent hydraulic troubles. Here is the problem: the raise, tilt and sideshift will intermittently stop functioning or move very slowly. Pulling the levers to the max will yield no improvement but when it gets a little more RPMs it will finally surge to full force. It is not a hydraulic supply problem from the pump as I have pulled the high pressure line off and checked that. I can get 1200 pounds easily at an idle before it stalls. I am thinking there is a bypass valve in the main control block that is hanging open that wont supply fluid to the mast function levers. Has anyone else come across this problem? Also, does anyone have access to a hydraulic schematic for this valve? Thanks for any help you can give.
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Since the p/s is not affected I would have the control valve serviced. This potentially could be a safety issue so I wouldn't put it off.
The power steering doesn't seem to be having any issues. The mast controls are just hesitant. I can hold any of the levers fully back and it starts off at a creeping speed and slowly speeds up until something lets loose and it is back to normal speed. And it only does it every once in a while. Maybe every 10 minutes or so with continued use. The other times it is fine.
This series powers the p/s through the hyd circuit- correct? When the unit is acting up, how's the p/s function?
you dont check pressures at idle
there are predetermined rpm ranges the pressures are checked at.
generally when testing hydraulic pressure it is tested at high rpm.
if you try and test at idle you will get an engine stall and you will never see what the actual relief pressure is.
You said it could build to 1,200 PSI at IDLE before it stalls the engine?
But have you gauged the pressure at high curb idle with the lift cylinders extended to full height?
"High curb idle" means governed maximum RPM with no load on engine.
Essentially that assures enough engine speed and torque that dead heading a control circuit will unseat the relief valve.
I replaced the main relief valve and changed the oil and filters. I have also tried cleaning the flow divider valve spool on the pump and the problem keeps presenting itself. Not sure where to look next.
I have a Hyster S80XL-BCS with the same problem. Have you and any success finding the problem?
1200 lbs seems like an awful low number......the relief valves in the hydraulic control valve are to be set @ 2773 PSI for lift and 2346 PSI for tilt...if you only have 1200 from the pump then the pump needs rebuilt/replaced.....
2 things come to mind here
1- main or return filter clogged up?
2- main relief valve spring broken?
might want to check that
-pull the filters ( i would also check the filter in the tank also)
-remove the relief valve and physically check it.
one more thing...
if this is a sectional valve worse case scenario is that it has a blown seal inside and is bypassing internally but i'd check the filters and main pressure relief valve first before taking the assembly apart.
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