dead telehandler boom lowering

This topic contains 4 replies and was last updated by electronexciter 10 years ago
January 14th, 2012 5:54pm
I have a Cat branded JLG TH514 (TBW serial # prefix)telehandler with inoperative hydraulics and the boom stuck in the air. The JLG service manual recommends connecting an auxillary power source with a 9 gallon capacity to the main control valve to manually lower the boom. Unfortunately our shop doesn't have any auxillary hydraulic source tooling to accomplish this. Does anyone have any recommendations on what to use for the auxillary hydraulic source? I'm interested in what other shops have come up with for solutions. I realize using the hydraulics on another machine is an option but I would like to set-up a portable auxillary hydraulic power unit that can be taken out into the field where other machines might not be available. I would like to avoid having to separate the lift cylinder's lock valve from the hydraulic cylinder because supporting the boom with blocking or stands, while it is hoisted with the crane, can be tricky if boom is high enough.
January 15th, 2012 3:46am
Firstly, you only need a small volume (3 t0 10 GPM) of oil, at a relatively low pressure (1000 to 1200PSI) to accomplish what you need to do. Next you need to decide what kind of power for this pump you want: a gas engine or electric motor. If you choose electric, will it be 12 volt, 24 volt or 120 volt AC.

This being the case, a power steering pump off a vehicle is likely all you will need and then select a driver for it.

If you select a P/S pump that has a hose to a remote oil storage reservoir, it will make it easy to construct. Make sure the power steering pump you select has a relief valve internally which makes for one less thing to worry about.

Use an open centre control valve. This makes it easier and a whole bunch cheaper. Cylinders and the like don't care about open centre/closed centre operation, only the pumps and control valves do. If, however, you decide the break into the machines system BEFORE the control valves, then you have to match the system.

The lock valves should prevent the boom from falling when you open it up. Be careful to loosen the line slowly before the lock valves and watch for boom movement. You should only lose a small amount of oil but there should be nothing that moves. The lock valves are likely pilot operated. Analyze whats happening there.

With systems like this, some of the biggest problem are cross contamination and dirt infiltration. Always keep these things in mind and keep it clean. You don't want to fix the engine problem and then have the machine come back for a new piston pump because of dirt.
January 15th, 2012 2:46pm
Jim, thanks for the tip on the power steering pump as a possible solution. I suppose since I would have gravity working in my favor, that the pressure setting of the internal relief valve on the power steering pump would likely not be an issue.
January 15th, 2012 9:31pm
Your welcome.

The P/S pump will likely have a working pressure of 2000 psi and a relief valve set at 2200 psi. The gravity your referring to will have to be controlled by an orifice. Your small control valve will function as that orifice to make sure that the boom does not come down too fast. If the boom comes down faster than the small pump can deliver the oil, you risk cavitation of the oil, and possible air being drawn in, bypassing the cylinder seals.

When air is admitted to a hydraulic system, this can cause what is referred to as the DIESEL EFFECT.

Go to: and see what you can find about cavitation, aeration and diesel effect.

Remember, too, that the P/S pump is likely to be a vane pump. That means it will not be self priming; make sure that you have a flooded inlet.
January 28th, 2012 9:52pm
Does machine have secondary steering?If machine has secondary steering from factory you have a problem solved.

Some machine which are using platform have secondary steering (auxiliary power) to lowering boom when engine is dead.

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