I use three separate systems. Gear up, gear down, and brakes. When I have had problems it's always been in the cylinders. Believe or not, mostly with BVM gear. I discovered that if you don't have a big pressure difference across the cylinder, like when you try to slow the gear by restricting the exhaust side, the o-ring would not seat and you would just lose all your air through the cylinder while trying to move the gear. I sequence the valves now such that I dump all the air on one side of the cylinder before I apply air to the other. I have not had any issues at all since I started doing this. With three separate air tanks (systems) I know that I am going to have air to get the gear down even if the up system decides to leak while I am in the air, and brakes when I get down. Important since I fly off of fairly short runways around here. Yes, it's a little heavier and costs a little more, but well worth it in my opinion. I also use heavy wall tubing (Dreamworks, etc.) Thanks for the heads up on tubing Airplane400.
Bryan