strange hydraulic phenomenon on U35-4 mini

[Jfet]

Hi guys,

Yesterday I was operating our new U35-4 mini and after using the boom/bucket and tracks to do a 60 degree lift swing turn, the boom decided it would not stay up. I immediately thought "oh crap I broke my new baby" and raised it up several times only to have the boom sag to the ground in about 2 seconds.

I was now thinking what a pain this was going to be to load up and take to the dealer, or if I could just take off the boom cylinder. I looked at the hoses and the valves inside the hatch and everything looked fine, no leaks.

I shut the machine off and turned it on again, same problem. I really could not see the cylinder developing such a huge internal leak so fast while doing nothing more stressful than lifting up the front of the machine a few inches, so I pushed off the ground again and powered back up in the air. The boom stayed up!

No problems at all after that. The boom did well for the next hour of work and has been up in the air all night with no sag.

Was this some sort of relief valve coming on and you have to power the boom up and down to reset it? Did I get some sort of air bubble in the system?

It sure did panic me!

 

[85Hokie]

Hi guys,

Yesterday I was operating our new U35-4 mini and after using the boom/bucket and tracks to do a 60 degree lift swing turn, the boom decided it would not stay up. I immediately thought "oh crap I broke my new baby" and raised it up several times only to have the boom sag to the ground in about 2 seconds.

I was now thinking what a pain this was going to be to load up and take to the dealer, or if I could just take off the boom cylinder. I looked at the hoses and the valves inside the hatch and everything looked fine, no leaks.

I shut the machine off and turned it on again, same problem. I really could not see the cylinder developing such a huge internal leak so fast while doing nothing more stressful than lifting up the front of the machine a few inches, so I pushed off the ground again and powered back up in the air. The boom stayed up!

No problems at all after that. The boom did well for the next hour of work and has been up in the air all night with no sag.

Was this some sort of relief valve coming on and you have to power the boom up and down to reset it? Did I get some sort of air bubble in the system?

It sure did panic me!

I hope for your sake, it was an air bubble - that could explain that sagging.
IF new - make your dealer aware of it and then write down all of this, and IF it happens again you'll have a paper trail.

 

[Jfet]

I hope for your sake, it was an air bubble - that could explain that sagging.
IF new - make your dealer aware of it and then write down all of this, and IF it happens again you'll have a paper trail.

Yes, I will let them know although it has not done it again in several hours of use since that one time.

My very limited knowledge of hydraulics leads me to speculate it was a either a sticky pressure relief valve for the lowering action of the boom but I don't know how those valves work. I am not sure when you ever really would trigger that relief except for the case where you are lifting the machine and turning it on the tracks, which might cause extra hydraulic pressure in the boom cylinder? Maybe it was the first time that valve had ever been actuated?

As of right now it would be a hard problem to reproduce and doesn't seem to be an issue, but I will keep an eye on it, thanks.

 

[Flienlow]

Plenty of Hydraulic fluid I assume?

 

[Jfet]

Yes, all fluids are normal. I have put another 10 hours of operation on the machine with no problems and I can't even reproduce the issue so either it was a glitch or it was the first time the boom relief valve had been operated and it was just a bit sticky. My guesses of course.

Anyway I still have 1 year 11 months and/or 1960 hours left on the warranty.