Hydraulic Cylinder bleeds down time to rebuild

[ovrszd]

This subject intrigues me. Wish I could get a grip on it.

With Brian's suggestion that a simple vacuum can be created with "nothing" there, wouldn't a heavily loaded cylinder simply create that vacuum and drop the load?? Isn't the reason it works because there is no air or vacuum or nothingness, only fluid, which cannot be compressed or stretched any measurable amount??

 

[Fawken]

Here is a great PDF that may help:
View attachment cylinders.pdf

And the link in case that PDF doesn't behave here:
http://www.google.com/url?sa=t&rct=...=sECIKjqWignlcMvkzj2w3Q&bvm=bv.95515949,d.aWw

 

[Fawken]

This subject intrigues me. Wish I could get a grip on it.

With Brian's suggestion that a simple vacuum can be created with "nothing" there, wouldn't a heavily loaded cylinder simply create that vacuum and drop the load?? Isn't the reason it works because there is no air or vacuum or nothingness, only fluid, which cannot be compressed or stretched any measurable amount??

In a word, yes. Study the diagrams in the PDF I linked.

 

[MtnViewRanch]

This subject intrigues me. Wish I could get a grip on it.

With Brian's suggestion that a simple vacuum can be created with "nothing" there, wouldn't a heavily loaded cylinder simply create that vacuum and drop the load?? Isn't the reason it works because there is no air or vacuum or nothingness, only fluid, which cannot be compressed or stretched any measurable amount??

Richard, do you have flow restrictors on your top and tilt set? If no, then with your box blade on, raise the hitch and tilt the box back fast and then stop. I will pretty much guarantee that you now have a vacuum on the tractor side of your top link. The fluid can not get into the cylinder as fast as the weight of the box pushes the fluid out of the rod side. Does fluid get in there, yes, but not enough to fill the void. Now let the box back down and watch the rod collapse back into the cylinder with no valve action. It is not full of air either, if the conditions were right you could actually watch the ram move in on it's own because of the vacuum and nature abhors a vacuum.

This has happened several times with my rear blade in the past.

 

[Fawken]

Richard, do you have flow restrictors on your top and tilt set? If no, then with your box blade on, raise the hitch and tilt the box back fast and then stop. I will pretty much guarantee that you now have a vacuum on the tractor side of your top link. The fluid can not get into the cylinder as fast as the weight of the box pushes the fluid out of the rod side. Does fluid get in there, yes, but not enough to fill the void. Now let the box back down and watch the rod collapse back into the cylinder with no valve action. It is not full of air either, if the conditions were right you could actually watch the ram move in on it's own because of the vacuum and nature abhors a vacuum.

This has happened several times with my rear blade in the past.

The top link is a single acting cylinder. Still, no vacuum. Behind a single acting cylinder piston there will be air - ambient pressure as described in the PDF. It relies on the weight of the link arms plus attachment to return to TDC.

 

[ovrszd]

My top link is a double acting cylinder.

I'll try Brian's test. I'll report my findings.

I do not have flow restrictors or locking valves on my cylinders.

 

[Fawken]

My top link is a double acting cylinder.

I'll try Brian's test. I'll report my findings.

I do not have flow restrictors or locking valves on my cylinders.

It's a ridiculous premise but, go ahead. All DA cylinders rely on fluid on both sides of the stroke to maintain stability. Otherwise they'd oscillate. Measure the vacuum with a Penning Gauge and get back to us.

 

[MtnViewRanch]

Here is a picture of a std tube type double acting cylinder. The rod goes in and out one end only. There can be hydraulic pressure applied to either side making it a double acting cylinder. A single acting cylinder that you are thinking about can only have hydraulic pressure applied to the flat (non rod side) of the piston.

So you are telling us that the hydraulic cylinders on your loader in your avatar are single acting cylinders? A cylinder does not have to have the rod coming out of it on both ends to be a double acting cylinder. A double acting cylinder is simple a cylinder that takes pressure on either side of the piston to make it move in the desired direction. It does not rely on gravity to collapse the unit as say, the 3pt hitch hydraulic does.

 

[Fawken]

No I'm not telling you that at all. I'm telling you there is no "vacuum" in the system. Gotta go to work. I know the physics of hydraulics. But it really does not matter as the OP was only being warned to not just assume his cylinder has a bad seal.

 

[Mace Canute]

No I'm not telling you that at all. I'm telling you there is no "vacuum" in the system. Gotta go to work. I know the physics of hydraulics. But it really does not matter as the OP was only being warned to not just assume his cylinder has a bad seal.

Sorry, but from what you've posted in this thread, that is an incorrect statement.