Leaking hyd. cyl, 400X Loader

[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,

Your illustrations was very good and clearly makes the case that the volume of oil on the rod side must equal the volume on the piston side. I have always been under the assumption that the rod side in fact has more cylinder space to accomodate the volume lost because of the rod displacement. I was not home when I sent my last post but did go to the Hydraulic Surplus ctr website and did my math using ram specs for a cylinder that had a total length that was about 5" longer than the stroke dimension-thereby verifying my theory that the rod volume is compensated by longer cylinder length.

However, when I got home, on Monday I fired up the 4720 and raised the loader to max height.

Extended rod length out of cylinder is about 20+ inches. Cylinder length I believe was about 22"- I didn't write it down because the difference was not enough to support my theory. In fact, the taps for the hoses on each end of the cylinder were around 20"-which further disproves my theory at least as far as JD goes.

Now I did have a conversation yesterday with a buddy who did work as a tech for the largest "green"dealer in MA. He currently is head wrench for a local highway dept and also runs a mobile Farm equipment repair business on the side. His take was seals on their own will cause piston "droop". He also is of the opinion that todays seals are nothing like they were in the "Old days".. I can attest to my experience on IH and Ford TLB from 40 years ago. I recall the packings were heavy andrather than having a flat face, had "v" section-thus they would stack up and form a more positive seal.

In any case, I have a couple of more guys that I have to talk to for a better explanation of the "cylinder much longer than the rod" issue.

Stay tuned. In any case, thx for taking the time to come up with your drawing- I would say that clearly illustrates the boom cylinders on a 400X.

 

[arlen4720]

Arlen,

Your illustrations was very good and clearly makes the case that the volume of oil on the rod side must equal the volume on the piston side. I have always been under the assumption that the rod side in fact has more cylinder space to accomodate the volume lost because of the rod displacement. I was not home when I sent my last post but did go to the Hydraulic Surplus ctr website and did my math using ram specs for a cylinder that had a total length that was about 5" longer than the stroke dimension-thereby verifying my theory that the rod volume is compensated by longer cylinder length.

However, when I got home, on Monday I fired up the 4720 and raised the loader to max height.

Extended rod length out of cylinder is about 20+ inches. Cylinder length I believe was about 22"- I didn't write it down because the difference was not enough to support my theory. In fact, the taps for the hoses on each end of the cylinder were around 20"-which further disproves my theory at least as far as JD goes.

Now I did have a conversation yesterday with a buddy who did work as a tech for the largest "green"dealer in MA. He currently is head wrench for a local highway dept and also runs a mobile Farm equipment repair business on the side. His take was seals on their own will cause piston "droop". He also is of the opinion that todays seals are nothing like they were in the "Old days".. I can attest to my experience on IH and Ford TLB from 40 years ago. I recall the packings were heavy andrather than having a flat face, had "v" section-thus they would stack up and form a more positive seal.

In any case, I have a couple of more guys that I have to talk to for a better explanation of the "cylinder much longer than the rod" issue.

Stay tuned. In any case, thx for taking the time to come up with your drawing- I would say that clearly illustrates the boom cylinders on a 400X.

Try this:
Raise your loader up, and disconnect the quick connects. Let it sit for a day. I guarantee as sure as the sun will rise in the east tomorrow, your boom will not drift down, even if you removed the seals completely.

I think allot of techs get confused on the difference between the behaviour of bad seals when we're talking retracting, as in the case of a boom, and extending as in the case of a bucket curl cylinder.
You're still not looking at it with the right logic. Even if you come up with a cylinder that has "extra space" it still doesn't matter. You still have a vessel filled with an incompressible fluid. You can't force a steel rod into it without fluid leaving the vessel. In the case of a loader boom valve/cylinder system, that can only happen in two ways:
1: External fluid leaks
2: leakage back through the valve.
Just come up with a cylinder with whatever dimensions you want, and we can work through it. Just remember my glass of water analogy.
While your at it, think about how the REGEN function works on the dump circuit of a loader.

 

[Red Horse]

Try this:
Raise your loader up, and disconnect the quick connects. Let it sit for a day. I guarantee as sure as the sun will rise in the east tomorrow, your boom will not drift down, even if you removed the seals completely.

I think allot of techs get confused on the difference between the behaviour of bad seals when we're talking retracting, as in the case of a boom, and extending as in the case of a bucket curl cylinder.
You're still not looking at it with the right logic. Even if you come up with a cylinder that has "extra space" it still doesn't matter. You still have a vessel filled with an incompressible fluid. You can't force a steel rod into it without fluid leaving the vessel. In the case of a loader boom valve/cylinder system, that can only happen in two ways:
1: External fluid leaks
2: leakage back through the valve.
Just come up with a cylinder with whatever dimensions you want, and we can work through it. Just remember my glass of water analogy.
While your at it, think about how the REGEN function works on the dump circuit of a loader.

Good idea on the disconnects-in the middle of another project (staining house-ugh) will monkey with it next week. And trust me- I agree 100% with you and Mr. Pascal! I'm just having a hard time with that extra cylinder length as in the example I used-

 

[dfkrug]

Now I did have a conversation yesterday with a buddy who did work as a tech for the largest "green"dealer in MA. He currently
is head wrench for a local highway dept and also runs a mobile Farm equipment repair business on the side. His take was
seals on their own will cause piston "droop". He also is of the opinion that todays seals are nothing like they were in the
"Old days".. I can attest to my experience on IH and Ford TLB from 40 years ago. I recall the packings were heavy and
rather than having a flat face, had "v" section-thus they would stack up and form a more positive seal.

Sadly, many technicians in the field are weak on theory. (Conversely, lots of theoreticians don't have much field
experience.) I can recall nearly 20 y ago, I was asking the head service guy at my local Kubota dealer how to
connect up some AUX hydraulics to my first tractor. He was very helpful, but did not BS me with theory he did
not know. Indeed, he told me on one occasion that, "I know this works, but I can not tell you why". I give him
a lot of credit for that.

When it comes to hydraulic seals, modern technology has made some big advances over the "old days". Not
only are there many configurations of piston, rod, and gland seals, there are numerous material types, including
urethane, tetra fluoroethylene, NBR, etc. (Teflon, Buna, Viton, etc). I suspect that back in the 1930s, when
fluid power was young, seals might have actually been mde of leather, as they did for carburetor accelerator
pumps back then.

Anyone interested is invited to look at any online catalog of seals from any big maker out there.

 

[Red Horse]

Well Arlen, I followed up on your suggestion, raised the loader and disconnected lines. You were correct-no drop whatsoever! I guess that effectively blows my theory out of water.

Now a new problem, can't hook loader arm hoses up-or should I say one or the other. I imagine this is because arms are "charged" in raised position. Any suggestions? I fooled with this for 45 min tonight, took turns bleeding pressure off by depressing center nub-only thing I accomplished was making a mess- still can't get both hoses connected. Any suggestions?

I have tried with engine on, off. Tried leaving last loader valve position "up", then "down" No difference.

 

[arlen4720]

Well Arlen, I followed up on your suggestion, raised the loader and disconnected lines. You were correct-no drop whatsoever! I guess that effectively blows my theory out of water.

Now a new problem, can't hook loader arm hoses up-or should I say one or the other. I imagine this is because arms are "charged" in raised position. Any suggestions? I fooled with this for 45 min tonight, took turns bleeding pressure off by depressing center nub-only thing I accomplished was making a mess- still can't get both hoses connected. Any suggestions?

I have tried with engine on, off. Tried leaving last loader valve position "up", then "down" No difference.

A bottle jack and a block or two under the loader should get the pressure off.

 

[Red Horse]

A bottle jack and a block or two under the loader should get the pressure off.

OK-willgive it a try in AM before sun hits it.

 

[arlen4720]

OK-willgive it a try in AM before sun hits it.

The fact that pressure is building on both ends of the cylinder, with a load, suggests that you do in fact have bad seals

 

[Red Horse]

The fact that pressure is building on both ends of the cylinder, with a load, suggests that you do in fact have bad seals

Well I did get it connected-so I thought, started machine, boom control worked, bucket locked! got off and saw bottom right hose (red) was out. I don't have a 400X manual and assumed bottom two connections were for boom. (Bought machine used and never had manual-when I sold my 3320 I gave new owner my manual-figured nothing in loader manual!)

What is proper routing of four hoses?
Thx

 

[dfkrug]

The fact that pressure is building on both ends of the cylinder, with a load, suggests that
you do in fact have bad seals

All raised loaders will do that when you disconnect the hoses, regardless of how good the piston seals are. Theoretically,
if the piston seals are "perfect", the rod side of the cyl will not be under pressure. But, you will find that in the
real world, even a brand new FEL will see pressure on both sides, making disconnected QA poppets hard to release.