Note: This guide is a work in progress. We’ll update it as we discover new locations.
Where to find Hydraulic Cylinder in FFXVOne of the locations in which you can find the Hydraulic Cylinder is in the Zegnautus Keep dungeon. As you walk around the area, eventually you’ll run across a conference room, with many screens displaying flags and some kind of 3D projector in the middle. After you kill the enemies, go around the central conference table and you’ll find the item there.
Like many other items that are labeled as treasure items, the Hydraulic Cylinder seems to be fairly useless to the player. Other than selling it for gil, it doesn’t appear to have any purpose. Hold off the selling just yet, though. The Hydraulic Cylinder is absolutely necessary to complete the Better Gravity Well quest. Essentially, once you get this item, you should pay Cid the mechanic a visit as soon as you can. Unequip the Gravity Well if it’s equipped, then give both the weapon and the Hydraulic Cylinder to Cid. Through his amazing tinkering skills, Cid will use the Cylinder to turn the Gravity Well into an improved version called Gravity Well II. This might take some time to complete, so you’ll want to do some side questing or cruise around in the Regalia to kill some time. When you come back to pick up the finished weapon, you’ll be awarded some EXP and a more powerful weapon.