forklift hydraulics.....2.5 ton Komatsu..

[frank horton]

need some advice......
for the last 6 months I have been having to rev higher and higher for it to lift 1 ton where it it should lift 2.5 easily.....
the hydraulic pump is driven from the timing chest and is quiet and does not get hot.....from the photo's the pump was built in 2005 and it's done no real work since....
there are no leaks at all and the fluid is clean, smells nice and at the correct level....
today I drained the tank to look at the filters, 1 for in feed to the pump and the other for the return to the tank....
both really clean..... the out feed oraffice to the pump is around 50mm above the bottom of the tank which is nice and clean with no bits or metal shards....
the pump is slightly lower than the outfeed.....so gravity does most of the work in filling the pump.....
have checked under the truck and all the pipes atre good with no damage....all pipes have guards....
there are only 2 motions, lift and powered forward and backwards tilt to the mast which works almost from tickover even with a load.......the third one on the right is not connected.....
so my first guess was to blame the valve body.....I planed to switch pipes so that the lift motion would be where the tilt was but with metal pipes it aint gonna be easy.....

So now have details of the pump and as I understand it it delivers 120bar at 1500 rpm but I may be reading it wrong....?
I downloaded a PDF on the HYdraulics and nowhere does it give a working pressure....plus it says its a spur geared pump
I need a gauge as it's my next job after filling the tank again and with new filters .....when I buy the correct gauge...so am I correct at 120bar at 1500 rpm..should I get a 150bar gauge....?
there is one blanking plug that I think is for the pressure gauge....white painted dot....square headed plug like a gas plug but v/small....
any other ideas out there please.....cant be without this machine for long.....
Have looked at the pricing of a

the upper pipe/fitting on the left is the high press in and the lower pipe with a wire hose clip is the return to the tank.....

I'm really stuck and outta my depth now.....
there is nobody near I can ask even if I spoke Greek.....hahaha....
thanks for looking....

 

[tigdlo]

The pressure and speed rating of the pump will be a maximum, and is probably regulated down lower than 120bar. You really need to find out the running pressure of the system for that exact model of forklift else any reading you take will be meaningless.

 

[Arclikeharrypotter]

If everything else works as should, then fingers crossed the pump should be fine. Attaching a copy of the hydraulic schematics maybe of help, but one thing you could check is the condition of the cylinder seals. That would be my first thing to check. I may have a pressure gauge you can have not sure what pressure it’s rated to.

 

[mattg]

Use an inline test port from e.g hydrotechnik or yes as you say stick a gauge in where the white plug is. Get a ~400Bar gauge, useful for most machines. Wild guess - is the lift function the right most spool? Looks like it has a relief valve. Check that is not jammed open. Anothe method would to check the relief pressure of tilt Vs lift by driving each to their endstop and observing the pressure on the gauge.

 

[dan.taylor.1]

Get someone else to operate it and listen or feel for the relief valve gping, if one function is fine its not the pump, its something after, assuming there's no visible leaks it'll be either oil leaking past the spool, ram seals leaking or relief valve bypassing early.

 

[Arclikeharrypotter]

Cylinder seal, if still a problem then check valve. Personally I don’t think it’ll be a relief valve as increasing revs, flow and thus pressure would only make it worse.

 

[mattg]

Cylinder seal, if still a problem then check valve. Personally I don’t think it’ll be a relief valve as increasing revs, flow and thus pressure would only make it worse.

Cylinder seal is quiet difficult to check though isn't it without taking it apart? Would you put the ram at its endstop and check for bypass flow on the non pressurised side? Any valve jammed open or leaking would behave as described - more revs equals more flow, equals more pressure drop across the faulty valve and so higher pressure to lift.

 

[carbon]

Cylinder seal,

I would have thought this was unlikely as the cylinder is single acting as it only has one connection to the spool valve. The non pressure side of the cylinder will have a vent of some description and surely a leak in the seal will have made itself evident in six months by lowering the oil level and leaking out of the cylinder vent.

 

[frank horton]

the mast rise valve is the left hand one....
one the mast is up even with a 1ton load it does not drop, even drunkenly....so think the rams are ok.....
where the high press inlet port is left side of the block, at the back there's what looks like a pressure relief valve....??
have ordered a gauge....
I'm still thinking the spool valve but scared to take it apart....must look to see whats inside.....
I was thinking that an O ring on it's piston vlave has let go giving bay pass for the pressure....
but are they metal seals in there.....? I\ve no idea....
thanks for the help....

 

[8ob]

Bringing the tilt back or lift to max while keeping the levers pulled back with the engine at idle should virtually stall the engine. If it doesn’t there is a pump or pressure release valve issue.

Bob

 

[merryman]

I would have thought this was unlikely as the cylinder is single acting as it only has one connection to the spool valve. The non pressure side of the cylinder will have a vent of some description and surely a leak in the seal will have made itself evident in six months by lowering the oil level and leaking out of the cylinder vent.

Never seen a cylinder vent pipe on a forklift that wasn't piped back to the return circuit,

Few points, Frank, you say the RH spool valve isn't used, that pipe from it must go to something and looks like it is open, so are you losing pressure down that valve? Spool valves are nothing special, simply superbly machined on bore and valve so, as long as you don't scratch them and keep things clean, they are easy to work on. They don't usually have o rings between ports, just on the top, to stop leaks to the outside. The white plug is a bit feeble. I used to work on Climaxes and the test port was more like that blue painted allen key fitting plug.