PISTON SPEED


Like the maximum operating temperature, the maximum permissible piston speed is based on the selection of seals in the hydraulic cylinder. In practice, a maximum piston speed of 0 .5 m/s (1 .64 feet/s) is generally assumed. If this is exceeded, a cylinder solution should be specially adapted to the existing requirements. The corresponding cylinder selection options are available, among other places, at www.ahp.de.

In like manner it is necessary to adapt a cylinder to the corresponding application if the piston speeds are very low. This is because so-called stick-slip effects occur that allow the piston rod to „judder“ in the micro area . This means that the piston rod moves in the narrow range between static and dynamic friction. At speeds of less than 0 .05 m/s (0 .164 feet/s), the friction is practically independent of the pressure.

 

 

 
Such an undesirable stick-slip effect is significantly amplified by yielding in the hydraulic system, such as air bubbles in the hydraulic fluid, and is generally connected with increased noise generation.

 

 


In the case of very dynamic applications, which also move large masses, heavy loads are made on the cylinders, the seals and the pressure fluid. The existing kinetic energy has to be deflected in a very short time. In such cases it is advisable to use hydraulic cylinders with integrated cushioning, and in the case of high loads also external shock absorbers. The cushining of the stroke is available in adjustable and non-adjustable options – depending on the type of cylinder and the piston diameter.

 

 

 
Cushioning only makes sense starting with a stroke length that is longer than the cushioned path, because otherwise the piston would only move within the cushioned path. This would result in long cycle times and increased power requirements, and would have to be taken into account in the design.