Loader leak down.

[boggen]

*waves a white flag* it finally clicked in me mind.



when i started to draw, and just about to open excel sheet to rough calc volume... for total hyd oil volume in A and B diagrams.
B = more hyd oil in the cylinder vs A diagram, that has less total volume of hyd oil in it.

thanks for keeping at me. was in the old fart mood, stuck in me ways and not about to budge.

 

[LD1]

Glad you got it. I had explained about as best I could, and was ready to throw in the towel.:laughing:

 

[boggen]

what makes for a better spool valve? or any hyd valve used on tractors today's age?

 

[LD1]

what makes for a better spool valve? or any hyd valve used on tractors today's age?

Tighter tolerances.

Remember, as JJ or someone else described, there are no seals in the valve. The spool and body only seal by the extremely exact fit of the spool. The seal is never perfect though. So a very tiny amount of hydraulic oil CAN and DOES leak past the valve. That causes drift.

Obviously, with no seals in the valve, the more pressure you have the faster it will leak. Thus hanging weight on the loader causes faster bleed down.

 

[arrow]

Glad you got it. I had explained about as best I could, and was ready to throw in the towel.:laughing:

LD is seldom wrong. He's got a good head for math and is conceptual, watch: LD, what percent increase is 74 over 70?

 

[boggen]

if hyd oil as it warms up, the viscosity changes, (from syrup to water). why would you want to have hyd oil constantly pumping through the system, warming itself up. vs a cooler / colder hyd oil. that is less likely to leak through and around the spool valve?

is there a better valve, that increases overall length and reduced diameter of spool valve within reason to help reduce leakage within the valve?

if metal to metal sealing, are there check valves inside the unit, that help reduce the leakage through the spool valve?

 

[dfkrug]

Obviously, with no seals in the valve, the more pressure you have the faster it will leak. Thus hanging weight on the
loader causes faster bleed down.

Yes. This animal has been beaten on TBN numerous times, but it is an important concept that bears repeating.

It is important to emphasize that loader boom (or hoe boom) bleed-down is the result of unwanted cylinder
retraction. If you get unwanted cylinder EXTENSION, as BRAIN55 points out above, then forces are trying
to PULL the rod out of the cylinder. Since the valve is closed, the rod-side fluid has nowhere to go. If the
piston seals are damaged (or missing), this force imposes a vacuum on the cylinder, resulting in air getting
sucked into the gland seal. Or cavitation of the oil (less likely). So the bucket or boxblade bleeds down
without any visible oil leaks, and you need to do more investigating before you can blame the
valve or piston seals, or both.

 

[J_J]

With all due respect to your ideas, thoughts and discussions, you all know the loader, BH, just about anything working with hyd, can and does leak

You want a perfect seal, then keep on dreaming.

You also know there are several factors causing it, and for some to say it can't happen is not totally true.

Whether the leak down is caused by the valve spools, cyl piston seals, temperature variation, vacuum leak bent shaft, bore out of round.. It could be one or several conditions that will cause leak down to happen.

In order to troubleshoot and perhaps save some money by purchasing the right part the first time, just might be to your liken.

It does seem like replacing seals fix most leakdown problems. It is the less expensive route.

If a valve spool does leak beyond your expectations, then you have to make a decision whether you want/need a new valve in order to keep your operating standards up.

However if the bad valve is costing you time and effort, then you have a choice.

Purchase new valve and install it your self or take it to a dealer and let them do it for a lot more money.

If you want factory, then buy factory.

You can probably do better using third party venders, and some logical shopping.

So, if you do not want leak down or poor performance, then fix it the best you can.

If you think it is spools, you can use needle valves to shut off all flow through the valve.

What to do about cyl.

To get the lowest leak down on those cyl, you are going to have to educate yourself on seals.

There are many types of seals, and if you choose correctly your leak free cyl might come to fruition.

There is no magic bullet here.

 

[LD1]

LD is seldom wrong. He's got a good head for math and is conceptual, watch: LD, what percent increase is 74 over 70?

5.7%

And 70 is 5.4% less than 74

 

[arrow]

5.7%

And 70 is 5.4% less than 74

74-70=4…… 4/70=.057x100=5.71%…..told ya.

Does anyone have a tractor that doesn't leak down a bit? It takes about 4 days for my fel to go down a foot. The 3 pt doesn't seem to move.

 

[J_J]

Seems like you have a tight hyd system.

How old is your machine?

How many hours on the machine?

Leakdown occurs differently for each hyd machine, even in the same year.

 

[arrow]

Seems like you have a tight hyd system.

How old is your machine?

How many hours on the machine?

Leakdown occurs differently for each hyd machine, even in the same year.

Oct 2013. Has 43 hrs. My other tractor started moving down almost immediately but that one was 28 years old.

 

[CJONE]

A cylinder will leak down with bad piston packing if the load is held by the cylinder under extension. The rod going out causes a vacuum in the base end but it still does not stop it from creaping. Less fluid in the rod end [because of rod volume] goes into the base of the cyl. I have had cylinders under extreme load [oilfield] blow the gland packing and/or o-rings out because high rod end pressure under compression but it still will leak down. Just been my experience, don't shoot me. When I design power units for industrial application I now use double PO checks because the quality of a standard control valve is so poor you cannot rely on them holding a cylinder in place anymore and most customers are too cheap to buy quality valves like Dynex. So like JJ said valve seals have nothing to do with cylinder holding. And technically for a double P/O check to work correctly the control valve has to be open to tank in the center position. [motor spool] CJ

 

[LD1]

So like JJ said valve seals have nothing to do with cylinder holding. And technically for a double P/O check to work correctly the control valve has to be open to tank in the center position. [motor spool] CJ

It does in our tractors and backhoes. Cause they dont use PO check valves. So if the valve leaks, the cylinder bleeds.

 

[J_J]

You all know the loader arms, BH boom, etc leak down. Some, more so than others. It is just a fact, and really no mystery.

If you really want to know what is leaking, install needle valves and you will know.

If you raise the loader up and close off the needle valve, and the lift arms drop down, you have your answer.

If you can force fluid past the piston seals, with opposite port open, then you also know your answer.

To check the pressure holding ability of the valve, a manual hyd pump with gage will tell you the story.

You can also set the relief valve using the manual hyd pump.

 

[CJONE]

It does in our tractors and backhoes. Cause they dont use PO check valves. So if the valve leaks, the cylinder bleeds.

You need to reread this. It says the valve SEALS have nothing to do with cyl holding. And they don't. I also understand how a tractor hydraulic system functions. I have repaired enough of them after others have messed them up. CJ

 

[CJONE]

You all know the loader arms, BH boom, etc leak down. Some, more so than others. It is just a fact, and really no mystery.

If you really want to know what is leaking, install needle valves and you will know.

If you raise the loader up and close off the needle valve, and the lift arms drop down, you have your answer.

If you can force fluid past the piston seals, with opposite port open, then you also know your answer.

To check the pressure holding ability of the valve, a manual hyd pump with gage will tell you the story.

You can also set the relief valve using the manual hyd pump.

Yep, I always USED to suggest putting a ball valve in at the cyl base. But anymore you have to be careful about liability. Sooner or later somebody will raise the loader and unhook the hose, I just know it!! CJ

 

[J_J]

The needle or ball valve is primarily for testing and working under the front of the machine.

I also use a cyl block to lock cyl.

 

[LD1]

You need to reread this. It says the valve SEALS have nothing to do with cyl holding. And they don't. I also understand how a tractor hydraulic system functions. I have repaired enough of them after others have messed them up. CJ

Technically correct.

But in the context of this thread, I assumed (maybe wrongfully) the valve-to-spool body sealing surfaces is what was being talked about. Even though technically there isnt a seal there.

 

[J_J]

I have seen this tolerance from different manufacturers on the valve spool to bore clearance on hyd valves when new.

Excerpt:

0.0002" diametral clearance is about the "Goldilocks zone" for hydraulic spool valves. Any looser and they leak down, Any tighter and they stick.


Then you have heat and cold, viscosities differences, and also wear and tear.