Hydraulic Cylinder bleeds down time to rebuild

[Fawken]

A DA cylinder will always have the same volume of fluid whether extended or contracted. Simple physics.

 

[MtnViewRanch]

A DA cylinder will always have the same volume of fluid whether extended or contracted. Simple physics.

Please explain how this is even possible??? :confused2:

When a cylinder is extended, there is more fluid in the cylinder than when retracted and the rod takes up volume.

 

[Fawken]

Please explain how this is even possible??? :confused2:

When a cylinder is extended, there is more fluid in the cylinder than when retracted and the rod takes up volume.

No there is not, as the seal acts as a piston in both directions. If it did not, it would be relying on suction to generate power on the down stroke. A simple bottle jack is a simple, Single Action cylinder which indeed does hold more fluid when extended. Think in terms of a double action air tire pump which pumps air on both the up and down stroke.

 

[MtnViewRanch]

I can't argue with that. :confused3:

 

[Fawken]

I can't argue with that. :confused3:

Depending on the design, the scenario you describe is possible. However, in such a case the cylinder would have more power on the up stroke (significantly more) and that is not desirable in our case where we need more power to raise/tilt back the bucket with a load or extract it from the dirt etc.
Now the calculation for the amount of force a 2" cylinder can exert under a given PSI is a product of the surface area of the piston in Cu inches and the maximum pressure in the circuit. Assuming 2000 PSI this would be 3.141414x 20000 if the rod mechanism took up no space- which it does so our final power would be a little less.

 

[SPYDERLK]

A DA cylinder will always have the same volume of fluid whether extended or contracted. Simple physics.

Perhaps it is a little more complex physics to recognize the volume taken up by the rod. This leaves more room in the cyl when it is extended/rod out. The area of the rod reduces the cyls pull force in comparison to its extend force, as only the annulus of the piston left outside the rod dia is available for the fluid to bear on. Due this situation the curl side of the circuit can see huge pressures when pushing or lifting with the valve centered.

Cyls having a rod on both ends with a piston in the middle do have constant volume and equal force each direction. Often used for steering. Perhaps these are termed DA cyls. ... I hadnt heard.
larry

 

[ovrszd]

Great video Brian!!!!

Also great discussion.

Wayyyyy over my head. But I understand the basics.

Larry described action that I understand and see displayed with hydraulic steering on our Buggies. If a dual end cylinder is used the steering speed and power is equal regardless of direction turned. If a single end cylinder is used the vehicle steers faster one direction and with more power the other direction.

Back to Brian's video for a second. Are you saying the cylinder displayed is defective, which is why you could extend it while full of fluid? If so, where did the matter come from to fill the void left when the ram was removed from the test area?? That one baffles me.

 

[MtnViewRanch]

Great video Brian!!!!

Also great discussion.

Wayyyyy over my head. But I understand the basics.

Larry described action that I understand and see displayed with hydraulic steering on our Buggies. If a dual end cylinder is used the steering speed and power is equal regardless of direction turned. If a single end cylinder is used the vehicle steers faster one direction and with more power the other direction.

Back to Brian's video for a second. Are you saying the cylinder displayed is defective, which is why you could extend it while full of fluid?

I removed the piston ring for this demo. According to you guys, I should not have been able to move the rod out with the rod retracted and both ends full of fluid. I obviously could by creating a vacuum. The thought was that something has to fill the void, so the rod can move. But nothing can get in, so nothing moves. But in reality, (I know reality sucks) the void created is just that, a void, a vacuum. There simply is NOTHING there.

If so, where did the matter come from to fill the void left when the ram was removed from the test area?? That one baffles me.

Richard, a vacuum is created in the non rod side of the cylinder. If you watch the video real close, when I first pushed the rod back in (@2:53 in the video) after pulling it out, the rod almost jumped in a couple of inches before it was actually harder to push. Those few inches of retraction were very very easy because of the vacuum that had been created.

 

[ovrszd]

I removed the piston ring for this demo. According to you guys, I should not have been able to move the rod out with the rod retracted and both ends full of fluid. I obviously could by creating a vacuum. The thought was that something has to fill the void, so the rod can move. But nothing can get in, so nothing moves. But in reality, (I know reality sucks) the void created is just that, a void, a vacuum. There simply is NOTHING there.



Richard, a vacuum is created in the non rod side of the cylinder. If you watch the video real close, when I first pushed the rod back in (@2:53 in the video) after pulling it out, the rod almost jumped in a couple of inches before it was actually harder to push. Those few inches of retraction were very very easy because of the vacuum that had been created.

I understand your theory. I still struggle with the vacuum idea. And because of that I can't discredit the possibility of sucking air in past the couplers and/or the ram seal. Which would be very hard to prove or disprove.

I appreciate your video very much. And I appreciate your patience in my education.

 

[Fawken]

I removed the piston ring for this demo. According to you guys, I should not have been able to move the rod out with the rod retracted and both ends full of fluid. I obviously could by creating a vacuum. The thought was that something has to fill the void, so the rod can move. But nothing can get in, so nothing moves. But in reality, (I know reality sucks) the void created is just that, a void, a vacuum. There simply is NOTHING there.



.

There is no "Vacuum" in a hydraulic circuit using DA (double acting) cylinders. And just to clarify, yes the rod does take up some space. So indeed there is more fluid in the cylinder when extended, however when discussing theory of operation it was easier for this discussion to omit that. There are sure fire ways to troubleshoot hydraulics using 2 or more gauges. Just disconnecting lines and or plugging them is like troubleshooting a circuit board by plugging in new components.