Moisture Class 3 air must be used where air is expanded direct into product, e.g. fluidizing nozzles in silos and reverse jet filters. Moisture Class 4 air may be used where expanded air is used in contact with product AND a pressure pot or long line is installed downstream of the regulator to minimise the risk of the cold air causing condensation.Moisture Class 4 air may be used on pneumatic conveyors using appropriately designed Laval nozzles.Air supplied to gas analysers, e.g. CO monitors used for explosion detection on egrons must be supplied with the grade of air specified by the manufacturer.