bucket drops

[SPYDERLK]

That is the most it will resist. Once it moves (if at all), unless it sucks more air in from somewhere, the resistance increases as vacuum increases on the cap end of the cylinder.

What is your position on retracting

Same as yours. Pressure has no limit. ... Vacuum does.

 

[J_J]

Mayee this article can shed some light on the subject.

How to troubleshoot hydraulic cylinder drift

It does seem odd though that when changing out the piston seals on a loader,, the lift arms and bucket stays up.

 

[LD1]

Mayee this article can shed some light on the subject.

How to troubleshoot hydraulic cylinder drift

Good article. So why did you say this earlier:

There is an exception to your theory, and that is, if there is a pulling load on the cyl it will extend the rod if the seals are leaking. .

Same thing if there is a load pushing on the rod, it will leak down if the seals are leaking.

 

[J_J]

If there is a seal leak,with a pulling load, the fluid will transfer until the pressure equalizes.

As you stated, the load could pull a vacuum.

 

[LD1]

If there is a seal leak,with a pulling load, the fluid will transfer until the pressure equalizes.

As you stated, the load could pull a vacuum.

Yes it can, but would reach equilibrium, and not continue to drift at the same rate.

But you are avoiding my questioning of the loader itself drifting down. Compressing a cylinder??

 

[J_J]

Well, answer this, do you think all loader arms descending over night is caused by valves?

Are you saying that it could not be caused by the cyl seals?

 

[LD1]

I am saying yes, it ain't the loader seals.

It can be the valve, gland seal leak, hose leak, but not the piston seals.

 

[SPYDERLK]

If there is a seal leak,with a pulling load, the fluid will transfer until the pressure equalizes.

As you stated, the load could pull a vacuum.

As soon as the port blocked cyl extends its volume increases. Since it is full a hard vacuum immediately develops on both sides of the leaky piston. Neglecting seal friction, the force then remains constant at 14.7psi X rod area as the cyl continues to its stop. This leaves an empty void in the cyl. The oil and any included water -- EVERYTHING VOLATILE -- boils into the void at ambient temperature raising the pressure slightly above 0 Absolute.
larry

 

[arlen4720]

As soon as the port blocked cyl extends its volume increases. Since it is full a hard vacuum immediately develops on both sides of the leaky piston. Neglecting seal friction, the force then remains constant at 14.7psi X rod area as the cyl continues to its stop. This leaves an empty void in the cyl. The oil and any included water -- EVERYTHING VOLATILE -- boils into the void at ambient temperature raising the pressure slightly above 0 Absolute.
larry

Sometimes the glands aren't very good at holding a vacuum though, and air is sucked in around the rod, and the whole process repeats. A situation that I've observed countless times on industrial press brakes.

 

[SPYDERLK]

Yeah, but then it just extends easier since the cyl holds a less complete vacuum.