鈉離子交換器是用于降低水中的硬度，生水由上而下通過交換器進行軟化，水中含有的鎂、鈣、陽離子與水交換劑的鈉離子互相交換；生水被軟化成為含極少的鈣、鎂、鹽水的水(稱為軟水)，可用于鍋爐給水及一些工業(yè)用水。由于鈉離子在水中有很大的溶解性。不會在鍋爐內部結成影垢，并且容易排出，經過鈉離子交換器的水，應該澄清過濾出來，基本少含有懸浮物。經交換器軟化后，其剩余硬度不超過0.03毫克當量/升。

The exchanging device is for reducing hardness of hard water. Raw water goes through the exchanger from top to bottom, to be softened by the sodium ion exchanger inside the device. Magnesium and calcium that contained by water are exchanged with that of sodium. Then the raw water becomes soft water containing very few ions of magnesium and calcium. The soft water can be used for feeding water of boiler and for some industrial uses. Due to its high dissolving ability in water, sodium ions will not form hard sediment in the boiler and can be easily removed. Raw water shall be filtered and settled with less suspended solids before coming into the exchanging device. After being softened in the device, the water?s hardness shall be less than 0.03mg equivalent.