Compressed Gas Cylinders – Oxygen is stored under pressure in a cylinder equipped with a regulator that controls the flow rate. Because the flow of oxygen out of the cylinder is constant, an oxygen-conserving device may be attached to the system to avoid waste. This device releases the gas only when you inhale and cuts it off when you exhale. Oxygen can be provided in a small cylinder that can be carried with you; either in a cart or a pack. The large tanks are heavy and only suitable for stationary use. These cylinders require no electricity