Hyster forklift need more lift power

   / Hyster forklift need more lift power #11  
Could be wear on the control valve spool.
   / Hyster forklift need more lift power
  • Thread Starter
I had thaught about spool wear but I can hang 3500 pounds on it, sit there for over a hour tried the lift function with motor off ans holds steady, if it had wear I figured oil would pass over the spool
   / Hyster forklift need more lift power #13  
Not necessarily. Most good quality control valves have load checks that keep trapped oil in the loaded cylinders sealed off from the spools themselves. This is a one way (single acting) spool, so it may or may not have the same checks as the tilt spool, but it probably has something.

Both the pressure and return lines to this valve are hard plumbed steel lines right? So not much chance of any easy experimenting with interrupting the return flow and actually watching it while attempting to lift a load. I would be tempted to try and separate the return line somewhere, add a hose of some sort and return the flow straight into the tank filler port. Run the engine and attempt to lift the load. If the flow stops or drops to a trickle that would indicate the pressure and supply just aren't there. If it merely slow a little and continues, then that would indicate an internal bypass in the valve somehow.

Again, without a gauge in there somewhere you're still guessing at things.
   / Hyster forklift need more lift power
  • Thread Starter
most of this machine are hard lines and yes the lift cylinder is single acting, the pressure line and return are at least 1 1/4 diameter it also runs into the transmission plus steering

have to find a place to tee in a pressure gauge
   / Hyster forklift need more lift power #15  
If it's all hard plumbed and there is no dedicated test port available, I would probably try to remove one of the tilts cylinder hoses, cap/plug the port and deadhead a gauge on the exposed hose end. See what that reads. Put all that back together and do the same on the lift cylinder. You should see a noticeable difference considering what it's doing.
   / Hyster forklift need more lift power #16  
When trying to lift a heavy load do any of the lines to the valve get warm or hot quicker than the others? If yes that is the line the flow is going to.
   / Hyster forklift need more lift power
  • Thread Starter
never ran it long enough to check what lines are getting hot, have to give that a try next time I have it running
   / Hyster forklift need more lift power #18  
Try swapping the tilt and lift lines on the valve block.

It is very likely that the valve sections have a safety relief behind the valves, so that it releases oil if you exceed the cylinder pressure by mechanical advantage, just like earthmoving machinery has.

Swapping the hoses at the valves is an easy way to pinpoint the failure.