1. Air exists in the cylinder, which can cause slide-down and climb-up of the piston when air shrinks and expands. To solve it, check the hydraulic pump, set up the exhaust unit and run the cylinder in full stroke roundly for several times until the air is discharged;
2. The quality of seals is connected directly with slide-down and climb-up. For an O-ring under working condition of low pressure, due to higher surface pressure and large difference between static and kinetic frictional resistance compared with a U-ring, it slides down and climbs up easily. On the other hand, for a U-ring, the surface pressure increases as the force increases. Although sealing effect increases relatively, the difference of static and kinetic friction enlarges too. Meanwhile, as interior pressure increases, the flexibility of rubber will be affected by the honed cylinder, as a result of which the contact resistance of lip edge increases, causing tilting of the ring and extending of lip edge. This is also a reason for slide-down and climb-up. To avoid such tilting, a support ring can be adopted to stabilize it;
3. Thirdly, inadequate of lubrication or poor finishing of bore of a honed cylinder can also accelerate wearing where relative motion exists like between piston and cylinder barrel, and that between tunnel and piston rod, causing such instability of slide-down and climb-up;
4. Acerbity sluggish inside the tube. Any possibility like improper assembly, deformation, abrasion of the parts inside the honed tube, and velocity variation as it travels caused by excessive resistance during running, mainly due to poor quality of assembly of parts, surface flaw or burned iron dust, adding the resistance and reducing the velocity, can also lead to such instability.
https://www.ht-tube.com/