Intakes
AND
Suction
Piping
C H A P T E R 10
SECTION 10.1
INTAKES, SUCTION
PIPING, AND
STRAINERS
WILSON L. DORNAUS
CHARLES C. HEALD
10.3
The most critical part of a system involving pumps is the suction approach, or inlet,
whether in the form of piping or open pit. A centrifugal pump that lacks proper pressure
or flow patterns at its inlet will not respond properly or perform to its maximum capabil-
ity. Uniformity of flow and flow control to the point of pumped fluid contact with the
impeller inlet vanes are the most important. Part of this may be controlled by proper pump
design, but the pit designer and suction piping designer have definite responsibilities to
achieve satisfactory pump operation. In open suction pit (wet-well) designs, the fluid flow
must be as uniform as possible right up to contact with the pump suction bell or suction
pipe, preferably without a change in direction or velocity.
Examples of dry-pit and wet-pit centrifugal pumps connected to open suction pits are
shown in Figure 1.
In dry-pit pumping, the pipe leading to the pump suction flange should not include
elbows close to the pump in any plane. Also, any other fittings which change flow direction
and velocity and which may impart a spinning effect to the flow should be avoided within
810 pipe diameters of the pump suction flange. Centrifugal pumps not designed for pre-
rotation of the fluid entering the impeller, either dry or wet pit, may suffer loss of efficiency
and an increase in noise if a spinning inlet flow occurs. Fluid rotation with the direction of
impeller rotation can result in a decrease in pump developed head. Fluid rotation against the
direction of impeller rotation can result in an increase in pump developed head and required
power, possibly overloading the driver as well as drastically affecting the pump curve shape
and performance in the system. If the total system is to operate efficiently and with mini-
mum maintenance, close attention to the suction environment of the pumps is required.
INTAKE STRUCTURES _____