Counterbalance valve Diagnosis

maytag said:

you can't depend on the designer to get things right, even down to the symbol as he may click and drag the wrong one.

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You got that right, I've run across errors on hyd as well as electrical schematics. Makes things a PITA to troubleshoot if the drawing is wrong. :Banghead

joelmartin said:

Well guys it has been a good learning experience for me. Gotta say I wish JLG Lull would hire tech support personnel with real world experience. Spoke with several and none of them could clearly explain how to isolate packings versus counterbalance valve malfunction.
We borrowed a known good valve, still drifted down; pulled cylinder and it will need some work internally. thanks for all who posted, the day I stop learning is the day I look for a new job with new challenges................Thanks again.

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Lull had some sharp guys when they where still in Minnesota. They were about they only ones who knew the pre-844C/1044C models. Unfortunately they were let go right before JLG bought Lull/Sky Trak. I know they were trying to start a telehandler service business in the Twin Cities area but I don't have any contact info.

ISZ

counterbalance/overcenter valve

You may hear the term "overcenter" valve, especially from an old-timer. When a load changes from resistive to tractive it's advantageous to have it configured like it was on the print I posted. Can't think of many applications in mobile equipment except maybe some of your aerial platforms may be setup this way.
That Vickers valve that was used had either a 8 to 1 or 16 to 1 pilot ratio so in addition to a lot of cylinder and hose failures a lot of horsepower was wasted and went to heat with the valve only setup to be direct operated.

Tom

icestationzebra said:

Another reason for counterbalance valves on telehandlers is to control the extend cylinder. Some have then on both sides of the extend to prevent a run-away condition when the boom is pointed down hill. ISZ

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which Lull should have done on my 1044B

I'm not an expert
Some selection criteria that I know is
1. Opertate in extreme environment
2. No problem when dealing with high pressure.
3. Providing hose burst protection
I think the article guide on counterbalance valve helps you the best.