Hydraulic Spool Valve Sticking

[Silvic]

I have a piece of equipment that has two sets of spool valves with a bank of six on each. One of the banks of SV's has a valve/lever that is a bit prone to sticking and has to be manually returned to the neutral position. I have wondered if there is some kind of debris caught in the valve but it does not seem to pass. Never had this before and am not certain what the troubleshooting tree should be. Any of the hydraulic gurus got a direction for me to start looking. The valve seems to function normally otherwise except it tends to stick in both forward and aft positions and does not return to neutral.

 

[kennyd]

I assume this is a "stack" valve, one that has multiple sections bolted together with long bolts? It could be that the bolts are to tight, or tightened unevenly. Perhaps it was leaking a bit at one time and someone tightened them to much rather than replacing the o-rings between the sections.

 

[J_J]

You can remove all the parts to that spool section and see if there is any debris.

Check springs and parts on the bottom of the spool section.

With all parts removed from the spool, slide the spool in the bore and see if it slides freely, and if so, look closely at the parts, especially the springs and washers.

There are torque specs for the valve.

 

[Silvic]

I assume this is a "stack" valve, one that has multiple sections bolted together with long bolts? It could be that the bolts are to tight, or tightened unevenly. Perhaps it was leaking a bit at one time and someone tightened them to much rather than replacing the o-rings between the sections.

No it is not a stack valve. One piece with 6 SV's

You can remove all the parts to that spool section and see if there is any debris.
Check springs and parts on the bottom of the spool section.
With all parts removed from the spool, slide the spool in the bore and see if it slides freely, and if so, look closely at the parts, especially the springs and washers.
There are torque specs for the valve.

Never taken one apart but looks like there may be a first time coming soon.
Any techniques or things to watch carefully for beside not losing parts and reassembling with correct torque values?

 

[J_J]

Do you have an illustrated breakdown of the valve?

On the bottom of the valve, thee are springs and washers, and if you have float, there are little springs and balls in the assembly.

Could that sticking spool be a detent spool, one that is supposed to stay in detent.

 

[kennyd]

No it is not a stack valve. One piece with 6 SV's

OK, one other simple thing to try: Loosen all the mounting bolts and see if it still sticks. Perhaps, if your lucky the surface its bolted to is not flat and the valve body is ever-so slightly twisted. It's worth a try...

 

[6sunset6]

I had that problem once and I was on the way to taking everything apart and found it was in the pivot for the handle. Big relief.

 

[SPYDERLK]

I have a piece of equipment that has two sets of spool valves with a bank of six on each. One of the banks of SV's has a valve/lever that is a bit prone to sticking and has to be manually returned to the neutral position. I have wondered if there is some kind of debris caught in the valve but it does not seem to pass. Never had this before and am not certain what the troubleshooting tree should be. Any of the hydraulic gurus got a direction for me to start looking. The valve seems to function normally otherwise except it tends to stick in both forward and aft positions and does not return to neutral.

Does it stick when there is no pressure? My 7520 loader curl sticks only when theres pressure - the more pressure the harder to return to neutral. I know the valve was damaged somehow by overpressure by pushing a stump bucket with the valve centered - no relief in this situation so pressure can go sky hi. I assume the spool is damaged but I havnt investigated. Like yours, the valve functions fine but just has to be manually centered.

 

[DLTTrekkers]

Thick mountingplate ? Loosen mountingbolts an check again !

 

[Silvic]

Does it stick when there is no pressure? My 7520 loader curl sticks only when theres pressure - the more pressure the harder to return to neutral. I know the valve was damaged somehow by overpressure by pushing a stump bucket with the valve centered - no relief in this situation so pressure can go sky hi. I assume the spool is damaged but I havnt investigated. Like yours, the valve functions fine but just has to be manually centered.

Yes it sticks with no pressure on the system.
I have found that if I move the valve back and forth multiple times (10-20) it does seem to get better but if left alone it always starts sticking again.

 

[DLTTrekkers]

And the answer was ?

 

[Silvic]

And the answer was ?

If you are asking what was found as a cause that is still the not so great unknown. Still doing it (sticking that is) but I have not yet rebuilt the SCV.that is last resort.

 

[DLTTrekkers]

Did you loosen the mountingbolts ?

 

[Silvic]

Did you loosen the mountingbolts ?

Yes no effect

 

[J_J]

Remove the lever for the sticky spool, and rotate the spool 180 degrees.

or

Remove the spool from the bore and inspect, clean.

 

[SPYDERLK]

Remove the lever for the sticky spool, and rotate the spool 180 degrees.

I did that to mine, referred to in post#8, and it had no effect. ... Does the lever conventionally drive the spool directly? And is the spool a single piece - no swivel in the middle?

The only explanation I could think of when turning it had no effect was that I wasnt really turning the valving part. :confused3:

 

[J_J]

By turning the spool 180 or removing it for inspection you might get rid of or see the cause of the sticky problem.

While the spool is out ,check the spool centering springs.