Hydraulic Creep or Bypass: Purchase a new control valve or install one load check valve, or two?

[Zork]

Greetings,

My bucket curl circuit developed a slight creep over the years and has gotten worse. I isolated the cylinders from the valve and the pistons held without ANY movement. Which led us to believe the bypassing is occurring in the valve.

What was strange is the creep/ bypass stopped after I had the hydraulic hoses changed on my backhoe some time back. Long story short, the system was opened and closed twice, and when everything was closed up the excessive creep that previously developed in my loader-curl circuit was totally gone! I thought the air in the system must have cleaned the debris in the valve because the bucket then held solid- if it didn't happen to me, I would not believe it.

I did not know how long will it last. After some light use the creep returned but it was much slower; now the creep/ bypass has returned and it seems the circuit is bypassing even more. I had previously thought the “HOLD” valves within the control valve were preventing this creep and debris would cause a creep, but now I understand the creep is coming from the excess clearance between the housing and the spool; especially since the bucket circuit does not drop faster than the creep when I transition the control valve from neutral to bucket function. I previously thought maybe trash had contaminated the hold valve and the air in the system had cleaned it.

My research into this creeping and solving it with a new replacement control valve indicates it could be a roll of the dice.

Therefore, I’m thinking of installing a load-check valve in the circuit and it would seem easiest and cheapest to install one (1) at the spool rather than two (one at each cylinder), thanks for reading and or replying to my thread.

Any thoughts?

 

[oldnslo]

If the drifting is random I would look very, very closely at all of the joystick linkage to the valve to confirm that everything moves freely. If the valve spool is not returning to spring loaded home position properly it can effect spool leakage rate.

 

[Zork]

Thank you, I will take a close look at that. For the longest time my rubber boot covering and protecting the linkage was damaged. I finally replaced it, but did not perform any cleaning other than blowing the area clean with my breath.

 

[rumwrks]

For the longest time my rubber boot covering and protecting the linkage was damaged. I finally replaced it, but did not perform any cleaning other than blowing the area clean with my breath

If your 3520 is like my 55 (mines newer but I think it should be about the same). The cables run from the joystick assembly on the fender down to the valve assembly. There are linkage couplers down on the valve assembly itself which are pretty easy to remove (just cotter pins) which would be a relatively easy place to isolate that problem (remove the cable connection, and manually activate the valves). There's a non zero chance the cables are either mis adjusted (they can stretch a little - there are adjustment nuts on the valve assembly side). Or more likely they're a bit sticky (the boot being damaged makes me think this is likely - a little moisture and you have a wee bit of corrosion in there..). A bit of some sort of lube run into the cables while you work them back and forth might do the trick to free them up. Something like CRC36 or another dry lube would be my first choice over oil (which could collect more gunk over time). You can also take the wire guide off of the underside of the fender pretty easily which would make it easier to poke around the cables if you pull them off of the valve assembly.

While you have the joystick assembly open, slap a little more white lithium grease on the ball joint connectors, mine were under lubed from the factory IMHO...

I got into all this while re-installing the 3rd function the dealer did a bit of a crap job of installing so I rerouted the cables (and hydraulic lines) to not be terrible and the laziest path possible. Which involved taking apart more than I actually needed to lol.

 

[Zork]

Thanks, the boot has been replaced. I had my mechanic stop in and remove the boot and disassemble the linkage.

The linkage was stiff and dirty. He cleaned lubricated the linkage with some special lube and cleaned and lubed the areas at the spools.

The controller certainly is much smoother but there is still some creep.

It seems if I raise the arms, then curl the bucket into bypass when the loader spool is in free-float and dropping, when it’s done the bucket curl seems to have less creep. Thanks for the advice.

 

[rumwrks]

The controller certainly is much smoother but there is still some creep.

Yeah I think isolating it to either the valve or the joystick/cable side would be my next step just to rule the joystick/cable side 100% out. You might well be right and it's a problem with the valves, but narrowing the problem down first would help make sure.

If there is some crud in the valve it *might* be possible to clean it out if you took it off and back flushed it. I've never done that so I'm not sure how painful it'd be but doesn't seem overly terrible (hydraulic coupler to a pump with some diesel to flush - I don't think it'd have to be super high pressure to just wash it out). I'd try that and maybe even taking the thing apart to try to clean it before replacing because I'm cheap

 

[rumwrks]

Another thought would be to swap the hydraulic lines to the loader around and see if the problem follows the valve or stays with the bucket curl... just to triple check that side of the setup (I'm not sure why it wouldn't follow the valve based on your explanation .. but I've been surprised before.. and usually opt for somewhat exhaustive checking of the easy things to check before moving to the harder stuff).

 

[Zork]

I’m sorry if I was not clear or if I misled you all, my controller is a joystick with the tie rod like linkage below the handle.

It would be easier to just replace the main valve unit. Is there any requirement or pass/fail rule for new control valves with creep/drift?

 

[oldnslo]

I’m sorry if I was not clear or if I misled you all, my controller is a joystick with the tie rod like linkage below the handle.

It would be easier to just replace the main valve unit. Is there any requirement or pass/fail rule for new control valves with creep/drift?

Some companies will publish leakage specs for their valves others do not. The other unknown is what leakage rate is acceptable drift for your loader design?

 

[LouNY]

Many hydraulic valves are spec'ed with a maximum leakage. Normally the more expensive the valve the lower the leakage rate.
I do not believe you would gain anything by "cleaning" or flushing the valve. If no creep is your desired outcome and you can live with slower dumping and response times you could add a pilot operated lock valve. Or a pilot operated check;

Otherwise a new valve would be required for less creep.