Is this normal?

This may be way off, but the load on the attachment in which the cylinders were detached had to be resting on the trailer somehow, unless they were bottoming out on the framework.

If the attachment was secured to the deck it would not move, but there was probably some suspension travel on the truck. The cylinders may have been detached so that they were not taking the pressure of the trucks movement relative to the lack of movement of the attachment.

I hope that makes sense, and it's just a guess.

 

2 way cylinders will only drift in the direction of extension if its bypassing internally. Its a weird concept to try and wrap your head around because you'd think it could drift either way.

The base end has more volume than the rod end due to the rod. If seals are bypassing the fluid runs from one side to the other. It can't escape because the control valve spool blocks it. There's enough room for displaced oil from the rod end to fit into the base end but not the other way around.

 

You and my farmer friend lost me at "it's a weird concept". All I really understand is that it's possible for hydraulics to move of their own volition, under the right circumstances, so disconnecting them in transit isn't a dumb idea.

 

1, the volume stays the same
2, the pressure exerted stays when the spool valve closes
3, the pressure can then move past the seals while only moving as much fluid as necessary to equalize on both sides of the seal
4, any leak in the system will bleed the pressure off and if it is on the "unpressured" side will cause creep.
In the case of a front loading refuse truck any creep even a small amount may cause the load to become over-height as they are normally over 11ft 6 inches in height on the ground and setting it on a RGN with a unloaded deck height of 20 or 24 inches means it is right at 13ft 6 in high and with any creep it is "oops! ticket time".
Note this is for used equipment or sometimes new where the hydraulic checks may have consisted of "look, no puddles".
You would be surprised at the indifference shown in inspections.

 

Rod end volume is less than the base end. The rod takes up displacement volume.