Midi Excavator boom keeps lifting

[Bearhead]

I have an IHi 55N3 (5 ton) that has hydraulic controls(not electro hydraulic). Was digging and the boom started lifting by itself. When pushing control to lower, it will eventually slow its lift and then stop, and then one can make it descend. As soon as one applies any lift/raise function, it starts back by itself to raise.
I took the valve body for the boom apart and did not find any debris or glaring issues, but i did service the valve while it was still installed on the bank for obvious reasons. Oil level is good and rest of the hydraulic functions are 100%. If I switch the controls to backhoe mode, it will replicate the same issue, but on hte other joystick, so that eliminates that actual hand controls. Any ideas? machine has 4000hrs and is very dependable(not now

 

[Ronsii]

So I assume you mean this machine has pilot controls.... sounds like a weak/broke spring or like you thought something is jamming/sticking the spool for the boom....

 

[uffex]

Good day
A starting point is to measure the spool shifting please see attached I hope it is of help.


Kind regards
Uffex

 

[uffex]

Spool movement

 

[92U 3406]

I'd put a gauge on that spool and verify the pilot control valve isn't flowing oil to move the spool.

 

[uffex]

Good day 92U
The only explanation is that the spool is sticking compare to a good one and measure the stop position.
Kind regards
Uffex

 

[Bearhead]

Thanks for the replies, I had a mechanic out and he too is baffled, however, neither of us are hydraulic specialists. Some more finds. We removed the boom spool, inspected closely and see no signs of damage or wear etc, it has free movement. The springs on either side appear serviceable and will still measure them. The additional notes on the issue. The boom will start to raise slowly if travel controls are actuated. I left the boom raised off the ground for two days and it never lowered, so there is no bypass on the valves(or cylinders). We took the boom cylinder apart and it checked out OK. I am in the Lenoir/Boone are in NC and am struggling to find a hydraulic tech to come and troubleshoot. A mechanic is one thing, a mechanic who understands hydraulic circuits is another:0
If anyone has someone to refer to come and help, let me know. Thanks
Attached is the schematic of a similiar machine, page 110 https://kattrak.com/wp-content/uploads/Service-Manual-KATO-IHI-55V4.pdf . I have the IHI 55N3

 

[John C.]

From the schematic it appears that the flow is to the top of the valve from the pumps and feeds down to the bucket first, then the boom and the rest of the functions afterwards. You mention that operating travel makes the boom creep up. Does that happen when you only operate the right track or do you have to operate both tracks? Does it matter which direction you operate the tracks? Does the boom creep up when you operate other functions? Looking at the pictorial drawing of the main control valve shows some other valves and controls having to do with the main control valve. Have you checked out those items yet?

 

[uffex]

Good day 92U
If you install a gauge to port "Pa2" this should be zero with the controls in the non operative position, this being the case it makes sense that operating the crawlers will increase the input pressure to the boom raise indicating a sticking or damaged crawler spool section (Cross over). If you need illustrations drop me a line, you can also plug the boom raise main line to confirm the diagnostics.
Kind regards
Uffex

 

[Bearhead]

Thanks John C and Uffex, I will check on which functions interfere with the boom. I have ordered a guage set and cap set to start isolating as you mention. Should have in a few days

 

[Bearhead]

Ok, thanks to all for the help. I got a pressure gauge hooked up to the pilot control for the boom lift function, pressure was correct, but would take a long while to depressurize. Followed the pilot line back, it T'd into a return spool valve, I dismantled this and the flow control valve and Voila, works as it should. this is after i had dismantled every other valve. Thanks for the help