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9.8.4.1 General

This section provides information and design recom- mendations for suction piping, required for all pumping applications, except where the pump inlet is immersed in the liquid. Proper design of suction piping is critical in that it determines the uniformity of flow delivered to the pump. Disturbed inflow causes deterioration of pump performance and may shorten pump life due to vibration and cavitation. Discharge piping has virtually no effect on pump performance other than the head loss that it creates. In this section, the term “pipe fit- tings” refers to all types of plumbing fittings, such as bends, reducers, tee and wye connections, and all types of valves.

This standard is intended to provide design recom- mendations such that the pump will receive inflow of sufficient uniformity to perform its intended duty. Other piping considerations, such as head loss, material selection, costs, and space requirements also need to be considered and are not covered here.

9.8.4.2 Principles

The ideal flow entering the pump inlet should be of a uniform velocity distribution without rotation and stable over time. This ideal flow is often referred to as undis- turbed flow, and it can be achieved by controlling pipe lengths and the type and location of fittings in the suc- tion piping system. The suction piping should be designed such that it is simple with gentle transitions if changing pipe sizes. Transitions resulting in flow decel- eration at the pump shall not used.

Section 45 Min.

PLAN

Pump inlet located in a confined pocket at least 1.5 bell diameters but no more than 2 bell diameters in plan in any direction

D/4

Vertical or steep slopes to pump inlet pipe covered with PVC Cone Greater of >2D 1.5-2.0 D D 1.5-2.0 D (2.0 ft/s max) 4D or S 0.6 m/s max Anti-Rotation Baffle

The velocities recommended in Section 9.8.4.3 shall be adhered to while keeping in mind that higher veloc- ities increase head loss and thus decrease the NPSH available at the pump inlet.

The effect of disturbed flow conditions at the inlet bell, i.e., at the beginning of the suction piping, tend to diminish with distance. Short suction piping is less effective in moderating disturbances before the flow reaches the pump. Good inflow conditions at the inlet bell exists if the intake is designed following recom- mendations in other parts of this standard. See Figure 9.8.18. The recommended inlet bell velocity is speci- fied in Table 9.8.3.

Part of the suction piping system can be subjected to pressures below atmospheric. It is, therefore, impor- tant to ensure that all fitting joints are tight, because air entrainment on the suction side may cause a reduction in pump performance and can be difficult to detect. Manifolds and suction headers are covered in Section 9.8.4.3.1.

9.8.4.3 Recommendations

The maximum recommended velocity in the suction piping is 2.4 m/s (8.0 ft/s). Velocities may be increased at the pump suction flange by the use of a gradual reducer. Higher velocities are acceptable providing the piping design delivers a smooth inlet flow to the pump suction as required in Section 9.8.5.6. The velocity in the suction piping should be constant or increasing as the flow approaches the pump.

For many common solids-bearing liquids, a velocity of about 1.0 m/s (3.0 ft/s) is required to prevent sedimen- tation in horizontal piping. A velocity as low as 0.6 m/s (2.0 ft/s) is generally sufficient for organic solids. There shall be no flow disturbing fittings (such as par- tially open valves, tees, short radius elbows, etc.) closer than five suction pipe diameters from the pump. Fully open, non-flow disturbing valves, vaned elbows, long radius elbows and reducers are not considered flow disturbing fittings (refer to Figures 9.8.19 and 9.8.20).

Figure 9.8.18 — Common intakes for suction piping showing submergence datum references

Table 9.8.3 — Acceptable velocity ranges for inlet bell diameter “D”

NOTE: See Figure 9.8.25A for corresponding inlet diame- ters (OD), calculated according to D = [Q/(785V)]0.5

NOTE: See Figure 9.8.25B for corresponding inlet diame- ters (OD), calculated according to D = (0.409Q/V)0.5

Pump Flow Range Q,

l/s

Recommended Inlet Bell Design

Velocity, m/s Acceptable Velocity Range, m/s < 315 V = 1.7 0.6≤V≤2.7 ≥315 < 1260 V = 1.7 0.9≤V≤2.4 ≥1260 V = 1.7 1.2≤V≤2.1 Pump Flow Range Q, gpm Recommended Inlet Bell Design

Velocity, ft/s Acceptable Velocity Range, ft/s < 5,000 V = 5.5 2≤V≤9 ≥5,000 < 20,000 V = 5.5 3≤V≤8 ≥20,000 V = 5.5 4≤V≤7

The suction pipe size is usually a larger diameter than the suction fitting on the pump. In such cases, a con- centric or eccentric reducer is fitted to accommodate the difference in pipe size. For horizontal suction pip- ing, the flat side of an eccentric reducer shall be located on the top. For vertical piping without bends

near the pump, a concentric reducer is

recommended.

9.8.4.3.1 Suction headers

A suction header, also called a suction manifold, is required when two or more pumps are fed from one common suction intake. Take-offs directly opposite each other are not allowed. The maximum velocity allowed in the suction header is 2.4 m/s (8.0 ft/s). If the ratio of the take-off diameter to the header diameter is equal to or greater than 0.3, then the minimum spac- ing between take-offs is 2 header diameters. If that same ratio is less than 0.3, the minimum spacing between take-offs is 3 take-off diameters. See Figure 9.8.22.

9.8.4.3.2 Submergence

For submergence of the suction header intake bell, see Section 9.8.7 and Figure 9.8.18 for calculation methods and datum references for S and D.