How many liters contain the cylinder drager pa 90?

Answer 1

That depends on the rated Water Capacity and Working Pressure of the cylinder and the Working Pressure. A regular steel cylinder has a Water Capacity of 6Litres and a Workig Pressur of 300 Bar. This means a Steel cylinder would hold 1800 litres (300 * 6 ) of compressed air.
Commonly used these days though are composite cylinders, made from Aluminium and Carbon Fibre. These are much, much lighter and also hold 6.8 Litres at 300Bar, thus holding 2040Litres