Hydraulic Cylinder Leak Down on Box Blade???

[Piston]

Well, it wasn't a leaking seal.

I did replace all the seals thinking that it was the problem originally, after tearing into it the originals appeared fine. On top of that, the exact same thing was happening before and after the new seals. This pretty much ruled out the seals.

I tried bleeding the air out and functioning the cylinder numerous times. I really didn't think there was air in there but wanted to make sure.


What the problem was, was a small metal shaving (I think it was a piece of the threads that must have stripped somewhere) that got stuck in one of those really small ports that the spring/ball check valve normally closes off.

That small shaving wasn't allowing the steel ball to seat and seal the port closed. I took it out and it probably would have been fine, but I ended up JB Welding those ports closed permanently.

I put it back together and tested it out, instantly it did feel better and a lot more solid. It didn't have any give in it. I know I don't know a lot about hydraulic cylinders but I'm fairly certain that neither the seals, or air entrapment was at all a contributing factor. However, all the tips and advice pointing to those is what ultimately led me to find the actual problem.

I took a pic and video after putting it all back together....then went in for supper...

Hydraulic cylinder, no leakdown - YouTube



I just came back up to the garage to check on it, and 3 hours later it has creeped (crept?) 3/4 of an inch. I'm happy with a quarter inch per hour


I still don't understand what those small ports are for? They are a type of check valve I suppose, but looking online at parts diagrams it seems most cylinders do t even have these?

Seeing that this cylinder is never under much stress, I didn't see a need to have check valve ports protecting it.

Regardless, I'm just happy it doesn't creep down in less than 10 seconds anymore! As an added bonus, I learned quite a bit in the process.

Never stop learning. . Thanks all.

 

[Mace Canute]

..........I still don't understand what those small ports are for? They are a type of check valve I suppose, but looking online at parts diagrams it seems most cylinders do t even have these?........

Just a really WAG but might they have been a pressure relief to allow the scarifiers to trip if they hit a very solid object and minimize damage?

 

[jenkinsph]

Just a really WAG but might they have been a pressure relief to allow the scarifiers to trip if they hit a very solid object and minimize damage?

Don't know but when you lower the rippers all the way down the linkage locks the bar in place. It can stop you in your tracks without releasing. That said if you do not allow the linkage to lock in the rippers will move out of the way easily.

 

[Piston]

I think your right. Not really knowing, but I imagine that is the intent, if the cylinder is shock loaded they would allow it to retract/extend before doing damage.
In this specific case I think that is unnecessary, only because when the scarifier bar is all the way down, the linkage engages a large steel "lock" so all the stress from the scarifiers is transferred to this "lock" rather than the cylinder. I'm sure this cylinder is used for many other applications which may need the shock loading pressure relief for protection.

 

[jenkinsph]

I still think air was in the cylinder in the video where the hoses were unplugged. I say that because if filled with oil where did the fluid go to displace the 4 inches or so of cylinder rod when it retracted. It did not compress and it did not disappear either.

 

[jenkinsph]

I think your right. Not really knowing, but I imagine that is the intent, if the cylinder is shock loaded they would allow it to retract/extend before doing damage.
In this specific case I think that is unnecessary, only because when the scarifier bar is all the way down, the linkage engages a large steel "lock" so all the stress from the scarifiers is transferred to this "lock" rather than the cylinder. I'm sure this cylinder is used for many other applications which may need the shock loading pressure relief for protection.

Matt, you may find if you miss locking up the bar and drive forward that you will bend up the linkage with those holes plugged. Just guessing here. When you look at the design of the linkage it is made for tension not compression, if the cylinder can't extend easily reducing this compression of the linkage it would be toast.

 

[Leejohn]

The check valves on the piston indeed are spick check valves. Mercruiser cyls has 4 with a floating piston.
2 large ones and 2 small ones. When you hit something the unit pops up and then returns to were it was set at, that is were the floating piston comes into play. If the cyls bottoms out to hard they might get jamed up and might not come down.

 

[Piston]

I still think air was in the cylinder in the video where the hoses were unplugged. I say that because if filled with oil where did the fluid go to displace the 4 inches or so of cylinder rod when it retracted. It did not compress and it did not disappear either.

It's entirely possible that it was just air, I just don't think it was. Here is my (not very confident ) explanation....

The rod end cap (the "inner" one, or whatever it's called) has two pressure relief ports in it. The pressure relief is made up of a stainless steel ball, a spring, and a set screw.
Like this...


I imagine the pressure relief is adjusted by screwing this set screw in/out to compress the spring more/less. The ball seats against the backside of the small hole that you see in the picture below...


Since the metal shaving was preventing the ball from seating, it was partially open all the time, allowing free communication of the hydraulic fluid to flow from one side of that cap, to the other.

Basically, it's as if I drilled a 3/16" hole in that rod end cap, leaving an easy way for the fluid to flow back and forth. This is why I think the cylinder was extending on it's own so quickly, even when the hoses were disconnected from the tractor.

I could be COMPLETELY wrong with this, but it's how I understand it.

 

[Piston]

Matt, you may find if you miss locking up the bar and drive forward that you will bend up the linkage with those holes plugged.

I really hope that doesn't happen.
I will be very mindful of it and hopefully not make that mistake. Knowing what I know now, I think I could have simply removed that metal shaving, tightened up those set screws, and been done with it. But, I didn't know that at that time.

If I did put a large shock load on the cylinder like that, I would think the tractors relief valve would open and allow the cylinder to move?

 

[MtnViewRanch]

It's entirely possible that it was just air, I just don't think it was. Here is my (not very confident ) explanation....

The rod end cap (the "inner" one, or whatever it's called) has two pressure relief ports in it. The pressure relief is made up of a stainless steel ball, a spring, and a set screw.
Like this...
View attachment 493691

I imagine the pressure relief is adjusted by screwing this set screw in/out to compress the spring more/less. The ball seats against the backside of the small hole that you see in the picture below...
View attachment 493692

Since the metal shaving was preventing the ball from seating, it was partially open all the time, allowing free communication of the hydraulic fluid to flow from one side of that cap, to the other.

Basically, it's as if I drilled a 3/16" hole in that rod end cap, leaving an easy way for the fluid to flow back and forth. This is why I think the cylinder was extending on it's own so quickly, even when the hoses were disconnected from the tractor.

I could be COMPLETELY wrong with this, but it's how I understand it.

Just to be clear here, the rod was extending, not retracting?

As far as the safety concerns others may have regarding those relief valves, all I can say is that I have sold several replacement cylinder units that I have made up for a couple hundred $$ vs the $500+ that Woods wants for their replacement and as of yet, no one has contacted me with any sort of problems. That's not to say that there won't be, but none so far.