In shower units, the water from the pipe where the mixer and/or closure valve is positioned, is conveyed to a rose at the end of the unit. The rose is often bell-shaped, closed at the bottom by the nozzle where a mass of very small holes are distributed, through which water, in the form of many minute jets, is sprayed like rain on the user.
The nozzle is usually made of plastic and has a cylindrical trunk shape with a hole in the middle via which it is screwed onto the rose or metallic supporting structure.
With another alternative, the edge of the nozzle is rolled over and held together with the rose by a threaded ring. Lastly there are other technical alternatives wherein the nozzle is attached to the rose which feeds it with the water to be sprayed.
Regardless of the type of anchorage and its particular shape, the nozzle is equipped with many minuscule holes which perforate it, in some cases having a cylindrical shape, in others having a shape that is initially a truncated cone and then cylindrical at the extreme that starts inside the rose.
A nozzle structure with spray perforations made in this way facilitates the formation and accumulation of lime scale therein, and therefore the blockage of these perforations so that the unit becomes unusable.
What, in fact, happens with the shower unit is, when the regulator for the water flow housed inside the pipes before the rose is turned off, not all the water comes out. A portion of the water remains in the rose due to depression in the pipe. Due to capillary and surface tension effects, the minuscule spray perforations retain water inside where it slowly evaporates due to the relatively high temperature that the rose reaches during the downflow of water which is normally heated.
Lime scale and solid substances dissolved in the water and incrustations, build up particularly around the fine spray holes until they cause them to clog up.
Following this, it is necessary to disassemble the nozzle and, remove it from the rose, clean it with liquid solvents capable of dissolving the lime scale or with fine needles which, when pushed into the perforations with the intention of freeing them of the lime scale, cause them to be widened and so, over time, the nozzle undergoes damage.