Cottrell CX09 trailer lifting issues

2 completely separate things here.

The first problem, trailer dropping when overlift engaged, is one of two things. Either the linkage for the overlift height control valve is broken, or the pilot valve is bad. Seems to me we just had this discussion with someone else a few months back, but I don't have time to search right now. You might scroll back through the threads, or search pilot valve. I think I even did a schematic, but not positive I did.

The 2nd thing is normal. Trailers, if they have a dump system at all, normally have a separate control valve to dump the trailer at the valve bank. I've never seen one tied to the tractor dump valve, although you could easily enough run another airline back to the trailer to do so. Generally, when you need to dump the trailer, it's much handier to do from the valves and not have to walk up to the truck to do so.

 

So I found the schematic, but it was for using a pilot valve to allow a shifter with different logic to replace an unavailable replacement, so no real help.

The pilot is an air-controlled selector which is used to determine which height control valve sends air to the bags. If it's bad, you'll be able to find it spewing air when the overlift is engaged.