Technical question about hyd cyl.

[J_J]

If I were to fill the rod end of a retracted cyl with fluid, and hung the cyl from a solid mount, and then placed a 2000 lbs load on the rod end pins, would the cyl move at all?

Is there a solid lock on the piston rod?

Will the load pull the rod to full extend or part way?

If the rod does moves will the piston rod move because of pressure, or just leakage or none of the above.

Could the load even cause air to be sucked in through the piston rod seal?.

If you install needle valves and raise a full bucket to full height and turn the needle valves to lock the cyl, what makes the lift arms descend over time?

If you have double check valves on a cyl with a load, will the cyl move over time?

 

[k0ua]

If I were to fill the rod end of a retracted cyl with fluid, and hung the cyl from a solid mount, and then placed a 2000 lbs load on the rod end pins, would the cyl move at all?I am going to assume the A and B ports are capped off and do not leak. Yes eventually the piston rod would move towards the earth due to leakagage around the seals

Is there a solid lock on the piston rod? no

Will the load pull the rod to full extend or part way? fully extended eventually all the fluid in the rod end of the cylinder will wind up in the cap end due to leakage around the seals. This may take a long time depending on how good the seals are, some may leak out the seals in the front too and drip off of the rod.

If the rod does moves will the piston rod move because of pressure, or just leakage or none of the above. well you have the 2000lb load attempting to pull the rod down, the fluid will not compress, but leakage will occur over time.

Could the load even cause air to be sucked in through the piston rod seal?.I don't see how air could be sucked in if anything fluid will leak out around this seal

If you install needle valves and raise a full bucket to full height and turn the needle valves to lock the cyl, what makes the lift arms descend over time?Leakage around the seals

If you have double check valves on a cyl with a load, will the cyl move over time?

The check valves are external to the cylinder so in your above scenario with the rod end of the cylinder full of fluid if the seals internally leak the fluid will leak into the cap end whether there are check valves on the ports or not. If the scenario was revversed and the cap end was full of fluid and rod fully extended and now a 2000 lb weight was placed on top of the rod, AND the seals leaked it would not go all the way down as the rod end fluid volume is less and the cap end fluid would fill it until it was ufll, then it would be up to the end seal if it leaked to allow fluid to continue to transfer from the cap end to the rod end to the outside world. The only time the check valves in each work port will make any difference is if the control valve is leaking and allowing fluid to transfer from the cylinder back thru the leaky control valve. The check valves would prevent this from happeining. All valves leak, all cylinder seals leak, even check valves and needle valves might leak some. Molecules of fluid are small, clearances are loose.

 

[oldnslo]

If I were to fill the rod end of a retracted cyl with fluid, and hung the cyl from a solid mount, and then placed a 2000 lbs load on the rod end pins, would the cyl move at all?

If the seals are good the cylinder should not move or will move very slowly.

Is there a solid lock on the piston rod?

No, not while trying to extend the cylinder there is not.

Q)Will the load pull the rod to full extend or part way?

A) Depends on the cylinder seals and the amount of time left hanging. It could fully extend if the seals leak enough.

Q)If the rod does moves will the piston rod move because of pressure, or just leakage or none of the above.

A) The weight hanging on the rod creates pressure which if the seal leaks will allow the cylinder to extend.

Could the load even cause air to be sucked in through the piston rod seal?.[/QUOTE]

If you install needle valves and raise a full bucket to full height and turn the needle valves to lock the cyl, what makes the lift arms descend over time?

If you have double check valves on a cyl with a load, will the cyl move over time?

If a cylinder is 100% full of oil and there are NO external leaks the cylinder will not retract. If they retract it is due to some external leakage. I.e. Needle valve or check valve leaking.

IF only ONE needle valve is used in the blind or base end of the cylinder then oil can leak past the spool of the directional valve and allow the cylinders to retract.


The Root Cause of Hydraulic Cylinder Drift

 

[SPYDERLK]

The fluid is being pressured and it has nowhere to go. Only leakage would allow it to move. Theres always some if it moves. Maybe a relief in the circuit on some examples you posited.

 

[the old grind]

If I were to fill the rod end of a retracted cyl with fluid, and hung the cyl from a solid mount, and then placed a 2000 lbs load on the rod end pins, .... Could the load even cause air to be sucked in through the piston rod seal?

This could be a trick question, er' depending on how it's interpreted (or jumbled ). Suppose both ports are capped and both 'ends' of the cylinder are full of fluid with 2k lbs trying to extend it. Fluid leakage past the piston seal(s) would allow extension over time, but there would also be suction created as the rod moves out of the cylinder and increases its total effective volume.

At that point, and secondary to piston seal leak-down, air would try to leak into the cylinder past a rod seal that's designed mainly to keep hydro in. Subject to leak-down (extension) air could enter all the more easily if not a 'double lip' type designed to contain in both directions. (.. what experienced folks put in trailer hubs, esp boat trailers).

There are a couple of threads/posts lately that mention checking the hydro fluid level. Rods take up volume when cylinders are retracted and manuals will recommend that cylinders be in a certain position when checking, so more cylinders o'all, or more in the 'wrong' position, can confound accurate level checks as we add on those extras. The hydro reservoir will take up the slack in total system volume, and is another reason (also heat expansion) that it must be vented.

J_J, thanks for another 'quiz' to get us thinking!

 

[MHarryE]

Cylinder quality - bore finish, seal material and design.

When you add load at first I would expect some drop as small pores were filled, but as you load up more it should stop and with a constant load stability should be reached.

Later as temperature changes occur the cylinder will extend and contract slightly due to fluid expansion because it's rate differs from the steel cylinder.

Rod end seals are more prone to leakage because of ensure to operating environment.

I found an old plow on our place that had the rear wheel cylinder fully retracted (rod end full) after sitting in a fence row at least 30 years after it was last used. The person who unhooked it raised the wheel above the ground rather than unhooking it with the wheel on the ground indicating that a cylinder with a full rod end will remain cons stand if the hoses are disconnected.

Pilot operated checks are much less prone to leakage than regular control valves. Still, our hillside combines equipped with POCs were prone to finding some combines leaning to one side months after they were left idle. We provided a mechanical device to prevent damage when the combine layer on its neighbor. POCs are not perfect either.

 

[Leejohn]

If you put 2000 lbs weight on the cyl. would your gauge show 2000psi more or less?

 

[k0ua]

If you put 2000 lbs weight on the cyl. would your gauge show 2000psi more or less?

That would depend on the surface area of the cylinder.

 

[J_J]

My thoughts on this situation is this.

If the cyl is filled and plugged, and if there is a perfect seal, the cyl will be in hyd lock.

Excerpt:

The volume of pressurized fluid on the rod side can easily be accommodated on the piston side. But as the cylinder drifts, a vacuum will develop on the piston side due to unequal volumes, and depending on the weight of the load, this vacuum may eventually result in equilibrium that arrests further drift.


If there was no or very little fluid on the base end of the cyl, you could pull a vacuum or suck in air past the rod seals.

 

[k0ua]

If there was no or very little fluid on the base end of the cyl, you could pull a vacuum or suck in air past the rod seals.

How are we going to suck in any air? the fluid in the rod side is under pressure, and if the end seal leaks, fluid is going to come squirting out with much more pressure than the ambient air pressure. The cap side port is sealed so it cannot leak in any air. I just don't see this air thing.