NMFIRE NFPA20 - 3.2.3 Concreting; 3.3 Suction Pipeline of Fire Pump

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III. Concentric reducer "figure A.3.3.1.3" is not allowed to be used at the pump suction.
Concentric reducer causes the suction pipe to produce airbags;
FIGURE A.3.3.1.3
IV. The supply pipe at the pump suction is not allowed to produce airbags, see “figure
A.3.3.1.4”;
FIGURE A.3.3.1.4
Concentric reducing pipe
Airbag
Suction
Pipeline
Airbag
Supply pipe
Suction Pipeline