Hi. I am working on a project which needs vertical turbine fire pumps. However, I have never experienced vertical pumps before. Regarding minimum submergemce of vertical pump suctions, I found an articles of NFPA 20 as below. Even though the code provides a detailed figure, I do not fully understand how I can determine the minimum submergence of the pump suction. My understanding of below clause is that the pumping water level at 150% of rated capacity is the minimum level to meet the pump NPSH required, so that If NPSH required level is within 10ft, the minimum submergence would be 10ft. above the second impeller. However, I think that my understanding is not correct since the 10ft submergence is too much. Please advise what is the correct way to determine the minimum submergency of vertical pumps as per below clause of NFPA 20.
220.127.116.11.2 Submergence of the second impeller from the bottom of the pump bowl assembly shall be not less than 10 ft
(3.2 m) below the pumping water level at 150 percent of rated capacity. (See Figure A.18.104.22.168.)