22
KM70
ENG_DEBEM S.r.l.
Rev. 01A-EN
01/03/2021
4.4.2 Suction piping
Suction piping plays a critical role in the correct operation of the pump-motor unit.
Suction piping must be:
• as short and direct as possible (length equal to at least 10 times the suction Ø)
• created according to best practices to prevent the possible formation of air pockets
• free from air inlets (critical points are the seals between the flanges and the seals of the valve
stems)
• with the inside diameter equal to that of the suction side of the pump
• with the inside diameter one size greater than that on the suction side of the pump in case of
longer pipes
The plant must have a Npsha (available) > Npshr (required)
The NPSHd value of the system must always be at least 0.5 m above the NPSHr of the pump (value re-
ferring to water at 20° C).
RECOMMENDED:
to eliminate air, set up the pipe as shown in the following diagram
Fig. 13
Recommended installation of suction piping.
AVOID:
piping that can entrap or obstruct the evacuation of air as shown in the following diagram
Fig. 14
Not recommended installation of suction piping.
Single-stage centrifugal pumps
not self-priming
always require that a suitable foot valve (check-valve)
is installed in all cases where pumps are positioned above the level of the liquid.
