Piston sealing is critical to proper cylinder function. Piston seals keep fluid from bypassing the piston which would otherwise reduce the pressure differential across the piston and in turn reduce the available force for the cylinder to perform work.
In 1962, E.F. Houghton Co. published A Handbook On Hydraulic and Pneumatic Packings for the fluid power industry. In the opening chapter there is an illustration of a “typical animal hide” which depicted the best parts of the hide that could be fabricated into leather “U” cups, “V” rings, and gaskets to seal fluid power cylinders.
You know that sinking feeling when you take the first bite of a much needed lunch, the phone rings and you answer to hear the words "We have a problem; it’s a new installation and the tube seals have blown!" With thoughts of catching a snack later in the day, you attend the scene of the crime...
There was a time, almost a generation ago, when the HH range of cylinders used an array of (normally) four metallic rings as the piston seal. Their function was much along the lines of the ones used in a car engine to this day.
These rings were inert to more or less anything the world threw at them. Heat was an easy task, aggressive fluids no problem and the working surface was so hard that the tube was more likely to wear over time than the seals were to lose their size.