Leaking hyd. cyl, 400X Loader

[arlen4720]

The rod side has a smaller volume of oil because of the volume of the rod itself. So as a cylinder retracts, the total volume of oil in the cylinder goes down due to the steel rod retracting into the cylinder.

 

[Red Horse]

The rod side has a smaller volume of oil because of the volume of the rod itself. So as a cylinder retracts, the total volume of oil in the cylinder goes down due to the steel rod retracting into the cylinder.

Arlen- thx for the continuing education. I hear you on the rod "volume" or displacement. But as the piston retracts, and as the length of the rod in the opposite side increases, so does the length of the cylinder bore-so in essence does that not balance out (I suppose I should do the math)???

In any case, my biggest issue is the load lifting capability. Like I said, I had one of those embarrassing moments when I tried to load a structure on a one ton last week. I was told it weighed 1200 and I should hasve been able to handle it no sweat. Instead I got it about 18" or so off the ground and that's all she wrote. Had to be rescued by Cat yellow!

 

[arlen4720]

The cylinder bore length is fixed. The only thing changing as the cylinder retracts is the amount of steel rod you are shoving into it.
Seals should fix you right up on the lift issue.

 

[Red Horse]

The cylinder bore length is fixed. The only thing changing as the cylinder retracts is the amount of steel rod you are shoving into it.
Seals should fix you right up on the lift issue.

Arlen-I didn't do a good job of explaining my point. What I'm saying is, say rod is extended-cylinder fully open and piston is on far end of cylinder and unit is at max length. as packings leak, oil gets on other side and piston starts to drop. Correct on volume of the rod itself. However, the volume of the cavity increases as the piston drops- cavity on extended side of piston increases, while cavity on closed side decreases. If you as an example assume a cylinder internal bore of 2" , that is 3.14 sq. in. of area or 3.14 cu. in for each inch of length. Assume a rod diameter of 1.25". That amounts to 1.2265 sq. in. of rod "space" or 1.2265 cu.in. for each 1" of rod length. So on the piston end of the rod, each inch of cylinder holds 3.14 cu. in. of oil. on the "extended" end of the cylinder, each inch of cylinder holds 3.14 cu in- 1.2265 cu in or 1.9135 cu in of oil. Thus 3.14/1.9135= 1.64" of travel needed on "extended side to equal 1" of travel on the piston end of rod.

Bottom line, seal kit AH 17625 should solve the problem.

 

[arlen4720]

Thus 3.14/1.9135= 1.64" of travel needed on "extended side to equal 1" of travel on the piston end of rod.

Bottom line, seal kit AH 17625 should solve the problem.

Mr. Horse,
Maybe it was me that didn't do a good job explaining things. In your above statement you say that it takes 1.64" of travel on the rod end to equal 1" of travel on the cap end. To that, I would ask, how would you make them travel different distances since they are connected?

Consider this example:
Imagine a nice tall glass of water that is 2 inches in diameter and 12 inches tall. Make sure it is filled to the top. Now take a 1.25" wooden dowel rod and lower into the glass.

Would you agree that water immediately starts spilling over the glass as the dowel is lowered in?
Would you agree that the amount of water that is spilling out is exactly equal to the volume of rod that has been lowered into the glass?

Take the example one step further:

Let's refill the glass, then put a tight fitting lid on it. Next let's punch a hole in the lid, and fit it with a tight seal to go around our dowel. We may need to replace our wood dowel with a nice piece of machined metal so we get a nice tight seal.

Now, with it all sealed up, and the glass filled with water, do you think you would be able to shove the rod into the glass?

My point is this....You can't shove a rod into a cylinder full of fluid without a place for the fluid to exit the cylinder. The amount of fluid that needs to exit is going to be equal to the volume of the rod you are trying to push in. Internal seals have nothing to do with it.
If a hydraulic cylinder is retracting, then fluid is leaving the cylinder somewhere. If it is not leaking externally, then it is leaking back through the valve.

An extending cylinder is different, as in the case of the curl cylinders on a loader. If you have bad seals, the rod will begin to extend, the bucket starts to droop, and a vacuum starts to build as the rod continues to extend out of the bore. The rod external wiper seals will start to pull in some air at some point if there is enough weight on the bucket. The wiper seals do a poor job of sealing a vacuum.

I also drew a little sketch of a cylinder and calculated a couple of volumes with the cylinder at 2 different positions.
View attachment Cylinder.pdf

I don't want this to turn into another one of those ugly threads that TBN is so famous for. I just wanted to give you some hydraulic troubleshooting tips.

 

[Red Horse]

Mr. Horse,
Maybe it was me that didn't do a good job explaining things. In your above statement you say that it takes 1.64" of travel on the rod end to equal 1" of travel on the cap end. To that, I would ask, how would you make them travel different distances since they are connected?

Consider this example:
Imagine a nice tall glass of water that is 2 inches in diameter and 12 inches tall. Make sure it is filled to the top. Now take a 1.25" wooden dowel rod and lower into the glass.

Would you agree that water immediately starts spilling over the glass as the dowel is lowered in?
Would you agree that the amount of water that is spilling out is exactly equal to the volume of rod that has been lowered into the glass?

Take the example one step further:

Let's refill the glass, then put a tight fitting lid on it. Next let's punch a hole in the lid, and fit it with a tight seal to go around our dowel. We may need to replace our wood dowel with a nice piece of machined metal so we get a nice tight seal.

Now, with it all sealed up, and the glass filled with water, do you think you would be able to shove the rod into the glass?

My point is this....You can't shove a rod into a cylinder full of fluid without a place for the fluid to exit the cylinder. The amount of fluid that needs to exit is going to be equal to the volume of the rod you are trying to push in. Internal seals have nothing to do with it.
If a hydraulic cylinder is retracting, then fluid is leaving the cylinder somewhere. If it is not leaking externally, then it is leaking back through the valve.

An extending cylinder is different, as in the case of the curl cylinders on a loader. If you have bad seals, the rod will begin to extend, the bucket starts to droop, and a vacuum starts to build as the rod continues to extend out of the bore. The rod external wiper seals will start to pull in some air at some point if there is enough weight on the bucket. The wiper seals do a poor job of sealing a vacuum.

I also drew a little sketch of a cylinder and calculated a couple of volumes with the cylinder at 2 different positions.
View attachment 387734

I don't want this to turn into another one of those ugly threads that TBN is so famous for. I just wanted to give you some hydraulic troubleshooting tips.

Arlen-first of all, nothing "ugly" about this thread. Keep in mind, I am the one seeking an explanation so I always appreciate anyone's attempt to educate me. I guess what confuses me, is I make the assumption that the cylinder is always LONGER than the rod length it must accomodate. In your example, you equate the cylinder length to what amounts to the rod length. I have this idea in my head that the cylinder length is LONGER by the amount of rod VOLUME it must accomodate. Thus when a rod is in fully extended position, the packings, piston, and retaining nut are in essence up against the end cap or snap ring/seal. The volume of oil in the cylinder than equals "X" and when the piston retracts, The added length of the cylinder on the retracted end is longer to accomodate the displacement volume of the rod.

Is that not the reason a hydraulic cylinder is always much longer than the length of the piston stroke-as in your illustration.:confused3:

PS Going back to my "youth" whenever a packing had to be changed, it was because the "boom" "dipper" "stabilizer" whatever was leaking down. I never remember having to replace a valve.

 

[arlen4720]

No matter how long or short the cylinder is, it still if FULL of oil. What about my glass of water analogy? Walk me through your logic with a similar analogy.
Cylinders are NOT generally "much" longer than the stroke, and even if they were, it isn't like there is an air space in there.
Draw a cylinder with the dimensions of your choice and work through it...calculate the total oil in the cylinder in 2 different places and let me know what you come up with.

 

[mguitas]

Watch the youtube , they will show ya how to repack them. After watching, i think i could do it myself.

 

[Red Horse]

Watch the youtube , they will show ya how to repack them. After watching, i think i could do it myself.

10-4-thx for input

 

[Red Horse]

No matter how long or short the cylinder is, it still if FULL of oil. What about my glass of water analogy? Walk me through your logic with a similar analogy.
Cylinders are NOT generally "much" longer than the stroke, and even if they were, it isn't like there is an air space in there.
Draw a cylinder with the dimensions of your choice and work through it...calculate the total oil in the cylinder in 2 different places and let me know what you come up with.

Arlen-will do