RV631 control valves have their main application in boiler feedwater process, They are expressly designed for processes that require low pressure drops when the flow rate is high and the need to avoid cavitation when flow rate is small. The special design of its cage, splitted in 3 steps along the travel, allows the RV631 trim to meet these process requests. During the first travel section, in which high pressure drops might generate cavitation phenomena, the process is controlled by a properly designed multistep cage, which causes the fluid to pass through six pressure reduction stages: in this way any vaporization is avoided. The last section has a final single stage cage with large flow passages which ensures the maximum flow rate with moderate pressure drop. Each section of the cage, welded together to form a solid rugged unit, is separated by lips that prevent the fluid passage between adjacent sections.