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

[Sodo]

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.

 

[oldnslo]

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.

 

[J_J]

Are you sure the cyl can't leak or bypass?

 

[Sodo]

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.

 

[J_J]

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.

 

[oldnslo]

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.

 

[Sodo]

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.

 

[oldnslo]

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.

 

[Sodo]

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.

 

[Sodo]

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

 

[oldnslo]

Sodo,
I used to design manifolds like this so bear with me on this.
"F" looks like a solenoid operated valve but not 100% sure. Are there any numbers or letters on the tag? This would be for electrically lowering the mast Vs manual. This could be a leak path and should unscrew.

Black device looks like a manual lowering valve. It could be a cartridge assembly or spring loaded. Unscrew it carefully in case it is under spring load so that parts don't fly out. Since this is what you have been operating to lower I would check this out first

Are any of the plugs labeled B - E directly across from the pressure port? If yes remove that plug carefully and see if there is a spring and ball under it. There could also be a threaded insert style check. I doubt the check is your problem but finding it would at least identify another potential leak point.

I would suspect that the rest of the plugs B - E are being used to block the drill paths required to machine the circuit in this manifold.

Good luck

I won't be checking this site until late tomorrow evening or Saturday some time.

 

[bulldogshotgun]

i'd say oldnslo is correct, and if i inderstood your diagram correctly when you operated the electric switch that was connected to the linkage one way the pump ran and the other it lowered? if thats the case the solenoid (F) is probably what lowers the forks the manual linkage is just a backup in case the solenoid fails or power is off.

 

[js5020]

Check the solenoid valve on the parker block and the switch the wires are connected to. The solenoid is a lock valve, its either stuck/broken or the switch is energizing it. The mechanical valve provides the rate of down, the solenoid should be the "lock". Its been a few yrs since I worked for Crown and my memory is "fuzzy" as our territory didnt have a pile of these to work on. Ill check back on the thread to see how you make out.

 

[Sodo]

Went to OMNI SEALS & PACKING for new o-rings. Sorry I intended to list the sizes (for forum completeness) but did not write them down. However they did say the sizes were standard.

I replaced the 4 O-rings and put it all back together, it still leaks down! :thumbdown:




There was some corrosion in the solenoid o-ring land but I cleaned it up.

OldnSlow I didn't see your post before reassembling! Thus I did not look behind any of the plugs, I thought they were just "plugs" but now it does make sense to me that there could be a checkvalve across from the pressure "in" port. It's "D", the biggest SAE plug and is across from the pressure "in" fitting.

The manual lower valve seat looks perfect, and the spring is pushing it pretty hard into its seat. It seems that when the manual valve seats, that is the 'lock'.

JS5020 Thanks very much for joining in, I still don't understand what the solenoid does. It gets 12v during the "up" (while the pump is running). I gave it 12v, it clicks lightly, and I can see a little movement. Could it be related to the 2nd stage of the mast? As there is a button switch that is pressed when the 2nd stage mast is at the bottom.

Here's whats inside the valve body again. (pics repeated from previous page)

I'm pretty bummed I did not open that bigger SAE plug to look for a checkvalve. JS5020, do you think I should go back in and look for a checkvalve behind that larger plug (D)?

 

[js5020]

The "black" part of the valve should control rate of travel (either up or down) and the "silver" solenoid either opens or closes the fluid path to the tank, it is what they call a "lowering valve". Remove 12v from it while lifting and if it is good it will hold the fluid from going back to tank and the mast should remain up. A similar setup is found on their pallet jacks except there is no provision to control the rate of drop, one just hits down button and that solenoid is energized and the forks go down, when they malfunction the jack will lift slow but immediately lowers once the raise button is released.

 

[js5020]

If you rotate that solenoid to show the bottom of the plunger it should be able to be dissambled and the plunger might be broke or bent causing it not to seal and allowing fluid to go right on by to tank,,, I dont think you can buy the individual parts short the coil or the complete stem but you can see of the plunger is what ails it.

 

[Sodo]

The "black" part of the valve should control rate of travel (either up or down)

Black valve controls the lowering. It has the 45d 'seat' for shutoff. A fairly hefty spring holds this valve against its seat and I couldn't see anything wrong with it (with a nakd eye). Depending on the valves position, the tapered diameter controls the down speed against gravity.

the "silver" solenoid either opens or closes the fluid path to the tank, it is what they call a "lowering valve". Remove 12v from it while lifting and if it is good it will hold the fluid from going back to tank and the mast should remain up.

Still having a hard time understanding the 12v valve, but thanks for trying! One of the leads comes from the motor solenoid terminal, so its given 12v during an "up" command (whenever the motor gets 12v). I suppose it loses 12v when the motor loses 12v. I'm going to have another look at it with your comments in mind.

I think I have to take it all apart again to look for a check valve. And I will have another look at the solenoid valve while in there, adreed if it's hot holding tight then it will bleed to rtn.
Do you think there is a check valve that takes the hold pressure off the pump? Or should I look for a check valve in the pump?

 

[js5020]

The silver solenoid allows the lower function, if its "on" through any means when lifting or when the control is in neutral the mast is going to come down.

Try this put everything back together and then unhook the wires to the silver solenoid, plug the truck in and select raise, unit should raise and hold position as long as the plunger in the silver solenoid isnt stuck in the open position.

To understand how most of these work,, lets forget you have an MT walkie stacker and lets say you have a Crown PE electric pallet jack ,,, now your pallet jack will raise kinda slow and when you release the lift button it falls back down without any imput by you. A PE has a similar electrohydraulic setup (but not the "black" flow control),, push the raise button and it causes the solenoid on the pump motor to close supplying voltage to the pump motor which spins the hyd motor creating pressure which causes the lift cyl to extend, let go of the raise button and all stops and holds. To lower the unit you would press the lower button which provides power to the coil on the lowering solenoid (silver solenoid on yours) the coil with + and - supplied now generates a magnectic field which causes the small poppet or plunger inside to shift and open the fliud path back to tank and the lift goes down. A Crown PE system has no provision for the operator to control the rate of raise or lower, its "preset" by the orffices in the valving and controlled electrically it requires no "mechanical" components to function save the function button, a Crown MT has the provision to allow the operator control of rate of raise and lower (black valve).

 

[oldnslo]

Sodo,
When looking at this manifold could you check a few items.
1) Is plug "D" directly inline with the pressure or pump supply port. If i would suspect there would be a check valve behind this.
2) Does the drill path below plug "E" connect to valve "F". Does it break into the threaded area of that valve cavity?
3) Does the drill path below plug "C" connect to the black manual lowering valve?
4) Is there a drill connection between the nose of the black lowering valve & the nose of valve "F". I.e if you remove both valve can you see straight through the manifold? Does this passage also connect to tank between these valves?
5) Does the drill path below plug "B" connect to the drill paths below plugs "C"& "E" and also connect to the cyl port?

If yes to all of the above I believe your circuit would either manually lower via the black valve or electrically lower via valve "F". Company i used to work for a had a Big Joe and tested a Crown and both of them had the option of manual lower with infinite speed control or electrically lower at some semi-controlled rate. Yours may not have this feature and work like js5020 says.

 

[Sodo]

your circuit would either manually lower via the black valve or electrically lower via valve "F".

Dang I forgot about the lower "button" on the Walkie steering handle. Yes that button operates the solenoid!

Tuesday I'm going to take that valve body all apart and look for a checkvalve, also look closer at the solenoid valve, maybe it's not closing tight. Thanks again you guys I hope you still have some energy for me next week. This weekend I'm on the Kubota (which has NO problems at all aside from being just too dang small)