The most significant elements the differentiate one softener from another is the volume of resin and the type of control valve.
Hard water passes through the resin bed to become soft.
During regeneration, water flow is reserved to backwash which cleans the resin bed. Brine is pulled in and then rinsed out to regenerate the resin, preparing it to soften more water. The brine tank is then refilled with fresh water for future cycles. The control valve body can be made of brass or plastic to fit any plumbing system. Regeneration cycles can be preset with a time control or can be based on water usage with a meter.