Mini Excavator Hydraulic Problem

[vongiese]

Hi - I have a 2016 Sany SY35 excavator with 350 hours. I bought it used a year ago. It is a 8500lb machine. The Boom deflection cylinder does not work. This cylinder pivots the boom at up to 90 degrees either direction from the cab so you can dig close to buildings, etc. It is operated by a foot pedal, and when I push on the pedal nothing happens - no whine from the pump - nothing. I pulled to pedal spool valve and blew low pressure air thru all orifices (couldn't figure out how to take it apart) and all seemed clear. This valve has no solenoids. I'm stumped. All other hydraulics work normally. I don't normally need to pivot the boom, but it has slowly moved and is off angle now. Even in the interim, if I could find a way to straighten out the boom I'd be happy!
Seems like it should be something simple....
thanks for any help.
VG

 

[dfkrug]

Sany may be the most common mainland Chinese excavator brand in the US. There seems to be west coast importers
in WA and SoCal.

First Q on your hyd problem: how many hyd pumps does it use?

Then: does the maker provide any hyd schematic docs?

 

[vongiese]

Thanks for the reply dfkrug - There is one pump and I have the hydraulic schematics...attempting to attach it....THe cylinder is labeled "BOOM SWING".
VG

 

[MossRoad]

If it were me, I'd swap the hoses for that cylinder with the hoses for another cylinder to quickly check if it's the valve.

 

[dfkrug]

Yeah, only one pump...looks like a variable-displacement pump.

My guess is that the nut fell off the rod inside the cyl, or the valve spool is faulty. I lean toward the latter, which
you can isolate with some hose-swapping as MOSS says.

If the valve, you may be able to slide the spool out without removing the whole valve stack. I was able to on my Chinese mini-X.

Let's hope it is the nut.

 

[vongiese]

Yeah, only one pump...looks like a variable-displacement pump.

My guess is that the nut fell off the rod inside the cyl, or the valve spool is faulty. I lean toward the latter, which
you can isolate with some hose-swapping as MOSS says.

If the valve, you may be able to slide the spool out without removing the whole valve stack. I was able to on my Chinese mini-X.

Let's hope it is the nut.

I'll swap hoses today and let you know what happens. Thanks for the advice MossRoad and dfkrug!!!
vg

 

[vongiese]

Yeah, only one pump...looks like a variable-displacement pump.

My guess is that the nut fell off the rod inside the cyl, or the valve spool is faulty. I lean toward the latter, which
you can isolate with some hose-swapping as MOSS says.

If the valve, you may be able to slide the spool out without removing the whole valve stack. I was able to on my Chinese mini-X.

Let's hope it is the nut.

Thanks for the advice MossRoad and dfkrug. I'm attempting to swap hoses today and find that adjacent hose fittings are all a larger size than the boom swing fitting. See the attached pic - it's the fitting with writing on it...hard to tell from the photo but if you look close you can see it is smaller than the rest. And the logical one to swap with is the thumb which is the very large one to the left. And I don't have stubby wrenches that can get at those fittings. Might be forced to take it to a repair shop....the machine is still under warranty - I just wanted to make sure it's not something simple and or not covered under warranty (i.e. dirt clogging a valve) etc. Any other ideas?
vg

 

[MossRoad]

Of course it's smaller. Why would life throw me a bone and make them all similar? :laughing: Well, it was worth a shot. You could get adapters for the size. But as you said, it's still under warranty.

 

[MossRoad]

What's the one just to the right of the one with the writing?

 

[vongiese]

The hose to the right is for the house swing, and it is slightly larger than the boom swing hose....
vg