Hydraulic Cylinder Operation

[NordTrac]

When a hydraulic function using a quick coupler works one way but not the other is about 99% a failed coupler or tip.

It was actually not working properly either way, regardless of how it was connected to the tractor hydraulics

 

[Hugo Habicht]

When a hydraulic function using a quick coupler works one way but not the other is about 99% a failed coupler or tip.

I read a lot about hydraulic couplers failing here. What is actually happening in the coupler so that oil cannot flow any more? Is it the spring breaking?