Crown 20MT Walkie forklift (lift-lower valve problem)

   / Crown 20MT Walkie forklift (lift-lower valve problem) #1  

Sodo

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Hi there, I have a 20MT stacker, it's an electric forklift. Everything works good except the forks leak down about an inch every 5 seconds. Listening in the oil tank I don't hear any fluid returning from above the packing so the problem has to be in the lift/lower valve. Its the aluminum block at center of the pic.

Does anyone have experience or advice rebuilding the lift/lower valve? A new valve from Crown is $377.
 

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   / Crown 20MT Walkie forklift (lift-lower valve problem) #2  
What is typically used on this type of system is a lift, check, and dump circuit. Normally there would be two valves that could cause the cylinder to drift. One is a mechanical check valve, the other is the solenoid operated valve. Parker usually has model codes engraved or stamped on their valves. i would carefully on the hex area of these valves to see if their is any identification.

Can you post a couple more pictures of the Parker manifold showing all of the valves.
 
   / Crown 20MT Walkie forklift (lift-lower valve problem) #3  
Are you sure the cyl can't leak or bypass?
 
   / Crown 20MT Walkie forklift (lift-lower valve problem)
  • Thread Starter
#4  
oldnslo, there are no other components, only this Parker valve block. To go up, you can see the electric switch that runs the pump motor. To go down there is a manually operated valve (and gravity). There could be a check valve to hold it when the motor stops. I don't think there are any solenoid operated valves but not sure what those wires might do (going out the bulkhead hole at the back of the Parker valve body). I can't "feel" any solenoid valves operating.

I think the "up" is the motor/pump, and maybe has a check if the pump doesn't hold positive.
The down is manually operated valve. I suspect the down valve is not holding.

J_J The cylinder packing is new. If the cylinder bypassed then there would be a LOT of fluid ontop of the piston, and when you rise it to the top of the cylinder stroke I would be able to hear this fluid blowing into the reservoir from the (cylinder top) return line. I have not opened this line to prove my theory, because I don't hear fluid coming into the reservoir at top of stroke (listening with the reservoir cap off). They are small lines I think it would make a lot of noise if fluid was blowing back into the tank.

I'd like to know how feasible it is to be able to fix this thing by tearing into that Parker valve block. Hoping its just o-rings but wondering what else might need attention in there.
 

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   / Crown 20MT Walkie forklift (lift-lower valve problem) #5  
Have you actually looked in that tank to see how the return dumps into the tank?

I am betting that the return to tank is below the level of the fluid. You might never hear the return flow.

On the tank for my hyd powered Power-Trac, all three return are about 3 in from the bottom.

I believe this is done to keep the aeration down to an acceptable level.
 
   / Crown 20MT Walkie forklift (lift-lower valve problem) #6  
SoDo,
If this mechanical lower then your lever is opening or moving some load holding valve. Can you see what the lever pushes on in the parker block? Is there a hex retainer on this shaft or valve? If yes you could try carefully removing this valve. I don't have a clue on valve style being used but I know companies make a push-to-open load holding valve so that may be what you have.

I would also suspect that somewhere in that manifold block their is also a check valve that isolates the pump from the load.
 
   / Crown 20MT Walkie forklift (lift-lower valve problem)
  • Thread Starter
#7  
Have you actually looked in that tank to see how the return dumps into the tank?
I am betting that the return to tank is below the level of the fluid. You might never hear the return flow.
......I believe this is done to keep the aeration down to an acceptable level.

Good point. I will open the return line and verify that it's not bypassing at the ram piston packing. That is a 5 minute test and it makes sense.

EDIT: I opened a return line fitting, it was "dry". Fluid has NOT passed thru this line (above the pistons) in a LONG time.

SoDo,
Can you see what the lever pushes on in the parker block? Is there a hex retainer on this shaft or valve? If yes you could try carefully removing this valve.

Yes the down lever moves a valve spindle, it is a hex nut and I suppose it will unscrew. I will look in there.

..... somewhere in that manifold block their is also a check valve that isolates the pump from the load.

Yeah that makes sense something to hold the load and bleed pressure off the pump to allow the next spin up to pressure, if the check was not holding then this bleed could be the inch/5sec leakdown I'm getting.

Great help guys, thanks for your attention.
 
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   / Crown 20MT Walkie forklift (lift-lower valve problem) #8  
Sodo
Can you tell if the pump/motor is spinning backwards while the unit is leaking down? If yes then the check is allowing flow to leak back through and driving the pump like a motor which would in turn spin the electric motor backwards.
 
   / Crown 20MT Walkie forklift (lift-lower valve problem)
  • Thread Starter
#9  
Sodo
Can you tell if the pump/motor is spinning backwards while the unit is leaking down?

Have not checked that because leakdown is absolutely silent no valve noises no fluid noises. Will look into that too.
 
   / Crown 20MT Walkie forklift (lift-lower valve problem)
  • Thread Starter
#10  
Got the Lift/Lower valve out. Can anybody tell me what these components do? I'm looking for the cause of cylinder pressure leakdown.
I'm going to unscrew the lowering valve, (the BLACK hex), that's the most likely candidate in my mind. What is the electrical device (F) at the other end?

Could there be checkvalves behind B,C,D,E?? Anything I should leave alone? Or go ahead and take it all apart?

EDIT: ADDED 3 more pics after I took it apart
 

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