1980's 60' boom lift hyd. control troubleshooting - same as tractor hydraulics?

[oldryder]

1980's vintage Terex 62C boom lift. simple (relatively) relay logic with small controller board at the joysticks.

Ground travel motion in "Forward" direction is full speed only. Other direction (Reverse) is nicely proportional based on joystick movement. Same joystick for both directions.

If there is a likely cause or this is a common problem I'd love to get specifics.

I thought I might swap the wires to the forward/rev solenoids. Since both are ground travel the brake should be disengaged either way. safe assumption?

If I swap the wires and problem moves then I know its controls, if not, a hyd issue.

Is "fail to wide open" a typical failure mode for a proportional control valve?

If there is a way to force the hydraulics to a slow speed only in "Forward" that would be an acceptable fix as I don't have to move the unit much and there is lots of space for turning. I'm guessing a flow control valve in the fwd hyd. circuit would solve things???

thx in advance for any help or suggestions.

Note I am fairly good at reading the prints and understanding the controls. Not so much on the hydraulics.

 

[J_J]

It would be nice for the proportional control to work properly.

In not possible, then a flow control valve like this would work for one direction, or a motor spool lever valve .

3/8 NPT HYD FLOW CONTROL VALVE W/RELIEF RDRS137-08

1 SPOOL 8 GPM PRINCE MB11C5C1 MOTOR SPOOL VALVE

 

[BukitCase]

I have an older scissor type lift (25 ft.) that has a similar problem, only no proportional - you might look at your joystick to see if it has a separate microswitch that decides whether a bypass solenoid gets pulled in (which would bypass a flow control orifice, for example)

Also, I believe there's one major difference between these and tractors - most tractors are open center, where most lifts are closed center (if electric controls) - so logic can be a bit different.

I thought I'd bookmarked a slow going (but informative) british tutorial that showed me (finally) how to interpret those wierd hydraulic symbols, but can't find it now.

This may not be what's confusing you, but it did me - you know those wierd little box diagrams with parallel lines in one section, X's in others, and T's in others? It finally hit me, that whole drawing represents the internal spool configuration - just picture the stuff INSIDE the boxes moving left or right, and the internal lines show flow (or blockage, in the case of the "T" -

IF that's one of the parts that's confusing, but my explanation is too, post back and I'll do a basic sketch... Steve

Forgot to mention - most of the boom type lifts I've used have a "boom down" switch somewhere that doesn't allow full speed unless the boom is below a certain point, not sure what that would do in your case but maybe a stuck microswitch? Hopefully you have prints for your unit, couldn't tell by your wording.

 

[oldryder]

Thx. for replies. I do have a set of elec and hyd prints but the hyd prints are mostly "greek" to me. I'll take another look at the prints based on your insight re: the symbols.

The rotate, boom up/down and boom in/out and the tilts on the bucket all work correctly. My single problem is the "full speed only" problem with the actual drive wheels.

 

[oldryder]

"you might look at your joystick to see if it has a separate microswitch that decides whether a bypass solenoid gets pulled in (which would bypass a flow control orifice, for example)"

joystick drives a pot from center CCW rotation for one drive direction and center CW rotation for other drive direction. I haven't figured out how to "hotwire" the controls so I can test the output of the joystick printed circuit board without actually moving the lift.

 

[oldnslo]

can you post the hydraulic schematic or at least the travel portion. Depending on how system was designed it may have a proportional valve feeding a bang-bang type valve. If the proportional valve failed open then the when the bang-bang shifts you would have full speed or no speed.

 

[oldryder]

can you post the hydraulic schematic or at least the travel portion. Depending on how system was designed it may have a proportional valve feeding a bang-bang type valve. If the proportional valve failed open then the when the bang-bang shifts you would have full speed or no speed.

Thx. for trying to help. I will try to draw up the relevant sections of the hyd print. and post.

 

[oldryder]

see attached drawing



http://i90.photobucket.com/albums/k266/oldryder/c62motorhyd001_zps3ff0ff66.jpg

 

[BukitCase]

"I haven't figured out how to "hotwire" the controls so I can test the output of the joystick printed circuit board without actually moving the lift."

Every lift I've ever run, large or small, was only 2-wheel drive.

Hint - do you have a hydraulic jack? ... Steve

 

[oldryder]

unit is definitely 4 wheel drive; you can see 4 wheel motors in the hyd. schematic. Unit also weighs 22,000 lbs so getting all 4 wheels off the ground would be a project all by itself.