Lull 644 - the counterbalance valve on the boom lift cylinder

[joestewart]

This is an early '90s Lull 644.

This telehandler has served well over the last couple of years, despite several minor problems. Its not used for business - just to accomplish a few heavy lifts out at the rural property.

Here's a new problem that has come up over the last month or so. The boom will slowly lower, even though the actuating lever is in the neutral position - seems to be getting worse over time. I'm pretty sure that this means the "counterbalance valve" on the boom lift cylinder has gone bad. Well, I looked up the part # P19064. This translates to LPP19064 on this vendor's website:

http://tiffinparts.com/products-and...-gradall-skytrak-and-lull-featured-items.html

Its one of the featured items in the link and there is a small photo of the valve.

My question: Is this a generic counterbalance valve that I could possibly hunt down from some other hydraulic retail establishment for a better price (JLG wants $583.33 for that little bugger!)? Or is this an item which is specific to this application and only available from JLG? Trying to save a buck here. I am not that well versed in hydraulics.

I'm going to try posting the same question over on the hydraulics forum. Thanks for any input!

 

[willie59]

It's far from generic, counterbalance valves for boom cylinders have very specific characteristics as required by the mfg. However, most of these type valve are built by some valve manufacturer, such as Sun, Hydro Force, etc. Sometimes you can find markings on these type of valves and obtain the exact valve from vendors other than OEM. Even then it's hit or miss at times, even though you know the mfg and the part number of the valve, as the valves are proprietary to the OEM.

 

[VoodooMojo]

It very well could be the counterbalance valve.
But:
The lift cylinder uses a single counterbalance valve.
This means that leaking piston seals or a loose nut on the lift cylinder's piston can cause the same problem.
It may be prudent to have the cylinder inspected before trusting luck on just the valve.

 

[willie59]

It very well could be the counterbalance valve.
But:
The lift cylinder uses a single counterbalance valve.
This means that leaking piston seals or a loose nut on the lift cylinder's piston can cause the same problem.
It may be prudent to have the cylinder inspected before trusting luck on just the valve.

Agreed.

 

[joestewart]

Thank you Gentlemen! This is the information I need to know. I rebuilt the boom lift cylinder myself about two years ago. It has worked great (until now). "Loose nut on the lift cylinder's piston"? - Man, that concerns me, because I can't remember if that nut was locked with an allen head set screw or what - I think it was.

I found this thread in the archives and will try the troubleshooting tips contained therein.

https://www.heavyequipmentforums.com/showthread.php?24548-Counterbalance-valve-Diagnosis

I hope I don't have to rebuild that cylinder again!

Thank you for the information on the proprietary nature of the valves - I'll buy from JLG if it comes to that.

 

[joestewart]

The link in the previous post didn't work. Here it is again.

https://www.heavyequipmentforums.com/showthread.php?24548-Counterbalance-valve-Diagnosis

Next cylinder I need to rebuild is #2 in voodoomojo's diagram. Leaks like a sieve out the shaft seal!