To avoid fractionation as the system is charged and for optimum system performance, correct type of cylinder has to be used for charging - if cylinder with dip-tubes are used, R-410A can be charged while the cylinder is upright. However, if the cylinder doesn't have dip-tubes, it should be kept upside-down to charge with liquid, not vapor, from the cylinder. The procedure, then, is to fill very slowly, the valve restricting output, in order to avoid slugging the compressor with liquid.