I used to design pressure sealing tools for the OG business. The industry is very old, so reliability testing and manufacturability are highly stressed.
Here are some publicly available examples that are very close to what I did.
The tools are called Packers. The restrain string movement and seals off pressure (Standard industry capabilities are about 10KSI).
Image Source (http://www.glossary.oilfield.slb.com/Terms/p/packer.aspx)
Here's a representational internal view from a catalogue
Representative animation of their operation.
This is what they look like in real life.
A typical manufacturing facility for machining the components.
We dealt with a wide range of materials, metal and non-metal.
Unfortunately, most of the details are not publicly available. It's astounding how much engineering goes into making sure this thing deploys miles down the well.