Spool valve stuck, flush hyd lines or not?

[MG84]

A few weeks back the tilt function on my Case 450C dozer stuck in one direction. You physically could not push the spool valve in the other direction, only neutral and tilt to the left. Took it apart by sliding the offending spool up and out of the valve block and sprayed some brake clean and compressed air down through the bore. It seemed to clean out whatever was in there although I never found the piece of dirt/metal. It did put a little nick in the edge of the spool but I cleaned it up with a file and all seems to be working fine.

Question is how should I prevent this from happening again or was it just a freak thing? Every hose on the machine is new but the steel lines are original. I'm guessing it could have either been a tiny fragment of wire from the new hoses that I missed or a bit of dirt from the existing steel lines. My thought is either leave well enough alone and run it, worst case I have to pull the spool out again, or flush the lines and risk dislodging whatever may be far enough down the lines that it's never going to get to the cylinder or valve anyways. If I flush it I could either pull both lines off the cylinder and pump some amount of oil through the lines into a bucket or connect the two lines together and just hold the valve in one direction to move a large volume of oil through and back through the filter. The spool I'm working with is the last in the stack and dumps directly into the tank return filter. Whats everyone's thoughts?

PS I'm posting this here instead of the dozer section because it's general hydraulics, not necessarily specific to any machine.

 

[nowing75]

Had a spool stuck on a skid steer last week and was caused by the cylinder rod was broke. Also had a dozer with a stuck spool and it had a bent rod that was scraping the barrel. I would make sure the cylinder for that circuit is good.

 

[MG84]

Had a spool stuck on a skid steer last week and was caused by the cylinder rod was broke. Also had a dozer with a stuck spool and it had a bent rod that was scraping the barrel. I would make sure the cylinder for that circuit is good.

As far as I can tell there is nothing wrong with the cylinder, everything is tight and working properly. I rebuilt all the cylinders about 200hrs ago with OEM seals and didn't notice any problems with them when apart. Maybe I should pull the lines and pump a little oil out each into a clean bucket to see if there is any debris near the cylinder end.

 

[Nige]

How about doing a filter cut and see what’s in it.? The quantity of particles might give you an idea of how potentially serious the problem might be.

 

[MG84]

How about doing a filter cut and see what’s in it.? The quantity of particles might give you an idea of how potentially serious the problem might be.

So in that case should I hook the two lines together and run a lot of fluid back through the circuit into the filter?

 

[Nige]

So in that case should I hook the two lines together and run a lot of fluid back through the circuit into the filter?

Not initially. Cut the filter and see what the inside looks like. Here is a link to a good Video on the process. Yes I know it's an engine oil filter but the principle is the same. Take photos of whatever you find and post them.

 

[Tinkerer]

A failing hydraulic pump is another potential source of metal contamination.

 

[MG84]

So the problem is back. After I 'fixed' it the first time by pulling the spool out and cleaning the valve block, I did go ahead and connect the two hydraulic lines together, held the valve in each direction for probably 5 min to send plenty of oil each way through the valve/hoses and back to the filter. All seemed good, got the machine out on a jobsite and within 15min the valve stuck again, same as last time.

A little more back story, machine had sat unused, outside for about 10yrs before I bought it. I replaced 15 hyd hoses and repacked all of the cylinders. Also did a full service with all new fluids and filters. I put about 200 trouble free hours on the machine since then, then the valve stuck. This filter is the one I installed and has ~200hrs on it.

Haven't done anything else yet except pulled the hydraulic filter and cut it open, here is what I found:





Went over the entire filter media and picked out any pieces I could find:


Can't tell if those are little bits of wire from the new hyd hoses or a burr off the cylinder threads from rebuilding them. Not sure about the other stuff, just junk floating around in an old system I guess. Any thoughts on how to proceed? My idea of flushing the lines back through the filter obviously didn't work.

 

[Truck Shop]

Friend had a similar issue with his tow truck hydraulic system, same scenario. Bought it-
had been setting for five years-California truck, all hoses were rotten/sun baked. His dad
has a hose machine, made his own hoses. Started having issues at control spools, he
didn't get hoses totally clean on assembly. Took awhile before issues started.

 

[MG84]

I hope I'm not in for long term trouble but who knows. I did blow all the hoses out with compressed air before installing them, but may have missed something, or I'm paying for a previous owners sins of not keeping stuff clean...

I'm thinking about pulling the spool out again, cleaning everything, then re-hooking up my loop on the circuit and letting it run fluid through for a lot longer this time. I've read on here about people hooking up a "kidney loop" on a contaminated hyd circuit with a filter and running fluid through it for an hour or more. Luckily this valve dumps right into the filter, then the tank. Also read about little foam plugs that you can shoot through a hyd line with compressed air to clean them out, anyone have experience with those?

 

[Nige]

Also read about little foam plugs that you can shoot through a hyd line with compressed air to clean them out, anyone have experience with those?

It's the last step in the SOP in the Cat world when fabricating a new hydraulic hose. The sponges are put into a plastic bag and zip-tied to the hose as proof to the purchaser that it's been cleaned.

https://www.hydraquip.com/wp-content/uploads/2018/02/ultraclean-catalog.pdf

EDIT: For badly contaminated hoses cleaning can be stepped up a level by using abrasive projectiles.

 

[1693TA]

Using the incorrect saw blade or abrasive blade to cut hydraulic hoses one of the leading indicators of that.

 

[Welder Dave]

I discovered there's special blades for cutting hyd. hose when I worked at a large industrial supply. They're a metal blade that has a scalloped type edge. I don't think they're used as much as they should be. Most places that aren't dedicated hyd. shops usually use abrasive chop saws. Blowing the foam plugs through usually cleans everything out. Contamination is listed as the number one issue for solenoid valves not working properly. It takes the tiniest particle to cause a problem. There's a few ways to get tiny amounts of contamination in a system. Internal wear is one possibility.

 

[1693TA]

I have a hydraulic hose cutting saw and that is the only thing it is used for. Curtis-Toledo is the brand and the blade is a smooth but high speed steel that thins from the middle to the cutting edge. It is not sharp but rather melts it's way through the rubber, and steel braiding leaving no burrs.

I usually pull a foam plug, (Greenlee) through cut hoses using an electrical fishtape kept for the purpose. Not so much because of trash from the hose cutting process, but rather I don't cap the ends of my bulk hose and dust/dirt/spiders etc. or something could be in the interior. Cheap insurance really.

 

[MG84]

Both if the places I use for hydraulic hoses have a special saw for cutting hose, as mentioned above the blade is steel and is more or less smooth.

I think I might buy one of those return filters for a log splitter and put some JIC fittings on it and move it from cylinder to cylinder location. Run fluid through it for an hour each direction, then cut it open and see what I find. Those filters are a lot cheaper than the $120 return filter on the dozer.

 

[1693TA]

Both if the places I use for hydraulic hoses have a special saw for cutting hose, as mentioned above the blade is steel and is more or less smooth.

I think I might buy one of those return filters for a log splitter and put some JIC fittings on it and move it from cylinder to cylinder location. Run fluid through it for an hour each direction, then cut it open and see what I find. Those filters are a lot cheaper than the $120 return filter on the dozer.

Any farm supply store will have filter bases and a 5 to 10 micron spin on filter readily available You can get hose fittings online easily. Lenz, and Cim-Tek are both pretty good brands and readily available all over.

However you know what the problem is now and once this is cleared the existing filter is all that's really needed. Can't you label and disconnect the hoses at the valve block, plumb in shop air and stroke the operator handles in both directions several times to purge the fouling matter? If manual spools pull them out and blow the cavities clean? With the hoses disconnected everything is open to atmosphere and easily done.

 

[MG84]

Any farm supply store will have filter bases and a 5 to 10 micron spin on filter readily available You can get hose fittings online easily. Lenz, and Cim-Tek are both pretty good brands and readily available all over.

However you know what the problem is now and once this is cleared the existing filter is all that's really needed. Can't you label and disconnect the hoses at the valve block, plumb in shop air and stroke the operator handles in both directions several times to purge the fouling matter? If manual spools pull them out and blow the cavities clean? With the hoses disconnected everything is open to atmosphere and easily done.

I'm going to try the 'kidney loop' first as it is easy, if that doesn't work plan B is the foam plugs. I'm worried just air won't clear the debris since the small particles mixed with hyd fluid could stick to the inside of the hoses and fittings.

 

[Nige]

I'm worried just air won't clear the debris since the small particles mixed with hyd fluid could stick to the inside of the hoses and fittings.

Don’t be. The projectiles will clean even oily hoses just fine.

 

[MG84]

Don’t be. The projectiles will clean even oily hoses just fine.

Yep, sorry if the last post was unclear, I meant air alone with no plug/projectile. I'll give the foam plugs a try if need be. One last question on those, how far do I need to take the system apart to blow those through? Can they make it around a hard 90* in a fitting?

 

[Nige]

Can they make it around a hard 90* in a fitting?

Depends on the diameter of the hose. Larger ones pretty much certainly. Smaller diameter ones I would personally put the projectile in at the elbow fitting end of the hose and push it round the corner first then apply air pressure. YMMV.