[supersonicsvt]

The compression fittings to use are the two-ferrule design, such as Swagelok (or Bylok, Gyloc, Circlelok, etc - everyone makes knockoffs). If you use this kind you will have no problems whatsoever. Even McMaster-Carr has their version. Just be sure to watch materials - if your PS hardline is stainless or carbon steel, you will have to use a stainless or carbon steel Swagelok fitting or else it won't "swage" the tubing. You can't use a brass fitting and ferrules on a carbon or stainless tube.

Make sure you debur that tubing ID!!!!