The invention relates to a descaling device which can be operated in an optimal manner with respect to the efficiency, descaling quality, energy and water consumption and is readily available. The insulative housing has a receiving space and a bottom wall located under the receiving space. The compensation sleeve, radially on the outside, is enclosed by a spring sleeve, which connects the lower valve-body section to the upper valve-body section and prestresses the compensation sleeve for pressure. In one embodiment of the invention, by elevating the inlet to the irradiation zone of the fluid treatment system with respect to the outlet, the amount of water that passes above the top lamp can be minimized, improving overall system performance. The needles are engaged by opposed loopers and cut pile hooks that pass between one another so as to engage the opposite row of needles for forming cut pile and loop pile tufts of yarn in the backing material.