Sumitomo LS118RH Crawler Crane's boom limit switch

[Ghashaan]

This crane's boom raising limit switch had been removed a few years ago and they have been operating it without the switch. Now they've asked me to install a new switch.

I found a four core cable that was taped at the end. There were 3 negative wires and 1 positive wire. I tried to figure out the circuits behavior by shorting the wires while the boom was in action. To my agony, none of the combinations that I tried worked.

There was no point in installing the limit switch as I have simulated all the different combinations of tests available.

Someone told me that the directional valve that's related boom might be physically actuated so that any electrical control would not apply.

Can anyone help me figure out a solution? Please give me some details about the physical actuation of directional valves and how to make changes to the configuration.

I tried Google for the schematics but nothing clicked. Maybe it's an old model that's discontinued.

Hope to hear some good advice.

 

[John C.]

You might try looking up a system for a Link-Belt crane. Sumitomo has been partners with and owner of Link-Belt for years. The model number is reminiscent of the Link-Belt model numbers. I've worked on LS218 cranes years ago but don't recall ever messing with a boom limit switch.

 

[crane operator]

John has you on the right track. The link belt and sumitomo cranes are mostly the same thing. Same basic machine, just japanese writing on the controls instead of english for a link belt. I would guess that the wiring that goes out to the switch is no longer in the "loop" with what controls the boom winch, that they have just totally bypassed that portion of the wiring.

Follow that cord back into the cab and see what it goes to. More than likely it has some kind of electrical coil that shuts off hydraulic flow to the winch motor. The current flows through the "limit switch" to the coil and holds open the hydraulic flow. If the limit switch is tripped, it shuts off the "coil", trapping the hydraulic flow to the motor.

This is only if the winch is a hydraulic motor operated winch. If its a old mechanical set up, it may be just a idiot light. I don't know the link belt numbers enough to tell you what it is.