I may have discovered my curl issues on my tractor

[Egon]

Double acting hydraulic cylinder. Fill both sides of cylinder with fluid. Block off both inlets to the cylinder. Now the piston rod cannot move to the left as that would require fluid removed from the cylinder. To move the rod left an amount of fluid equal in volume to the new rod in the cylinder must be removed.

The rod can be moved right as withdrawing the rod leaves room for fluid in the cylinder.

Take the piston off and just leave the rod it all works the same. The rod can't move to the left as there is no place for the fluid to go. Move it to the right and withdrawing the rod makes room for fluid.

 

[LD1]

^^^ spot on. Except if piston seals are good, rod also cannot move to the right. As fluid cannot bypass to the side where "room" was created for it.

That's why if the cylinder is drifting in extend mode (to the right in your diagram), it can be EITHER the seals OR the valve.

But if the cylinder is drifting in retract mode (left in your diagram)....it ain't the seals. It's the VALVE

 

[rback33]

It's alot of math, but doing it can tell if you are in spec for the valve.

We have established your leak rate at 1/4" per hour AT THE CYLINDER.

A 45mm bore cylinder is common for that size machine. So I'll assume that is what it is (but could be a 50mm).

45mm is 1.77". So with a little math, over one hour, two cylinders are bleeding off 1.23 cu in of oil (lift cylinders not curl)

I couldn't find specs on the valve you listed. But calling them, (it's a brand valve) or Calling the mfg of your current valve, you should be able to get a spec for maximum spool leakage.

Here is a generic 10gpm valve. VALVES | Trausch Dynamics
Notice they list 0.732 cubic inches a minute @ 1450psi and 120 degrees.

Assuming you have 45 mm cylinders, if you carried a load that required 1450 psi to hold (about 50% of your loaders capacity) over that same hour you would have leaked 44 cubic inches of oil out and still be considered acceptable. (Your cylinder would have compressed 9" instead of 1/4" in an hour.)

So like I say, without knowing specs, it's all opinion.

What does that 1/4" per hour equate to at the bucket? Usually on the lift it's about 5:1 ratio. So if your loader is drifting down a tad over an inch in an hour, I think your dealer is going to say it's within spec and tough luck.

And changing valves may not help. It might even make it worse

We do not build that loader, but this post is spot on. Your valve is going to be within spec and you very well make it worse by changing it.

I am glad you did go back and do measurements on the cylinder which is the only way to properly check the leak down. All loaders built by KMW come with instructions for checking the leak down in the manual.

 

[aerojunkie]

Update......I went and talked to my dealer yesterday and he basically said the same thing that had been mentioned here. That a little bit of drift in the amount I was getting is the norm and really nothing to worry about. Thank you again to all the people that have posted and all the information was greatly appreciated.

 

[redobbin]

This is the best explanation I've seen. Well worth the 6 mins.

Bypass testing a hydraulic cylinder - YouTube

Excellent