2.2 Selection of Pump
2.2.1
The schemes of pump type shall be proposed according to the operating head of the pumping station and operation characteristics,and the final selection shall be determined by technical and economic comparisons.
2.2.2
The number of main pumps shall be determined by tech nical and economic comparisons,considering the followings:
1 The task and scale of the pumping station,operating mode and operating time.
2 The characteristic water levels of the inlet and outlet pools,and the regulation characteristics of pumping station.
3 The conditions of project layout and transportation.
4 The manufacturing capability.
5 Other special requirements.
2.2.3
For the important water supply pumping station and irri gation pumping station,the standby pump group shall be set.The number of standby pumps shall be determined according to the importance of the pump station,storage capacity,operation conditions and annual operating hours.For the pump station with fewer annual operating hours,the standby pump need not be installed.
2.2.4
For large-sized pumps,the device model acceptance test shall be performed.If the inlet and outlet water passage of the existing hydraulic model have been changed greatly,the device model test shall be carried out again.
2.2.5
Following factors shall be considered to determine the pump rated speed:
1 The rated speed of the pump shall be selected according to the parameters such as the head and flow,diameter of the impeller,cooperated motor speed series,etc.If two or more speeds are available,it shall be determined by technical and economic comparisons.
2 The pump that operates at adjusting speed shall be in safe and stable operation within the whole range of the operation head.
3 The rated speed should be appropriately reduced for the pump pumping from sediment-laden water source,working under the condition of large variation of head or high altitude area.
2.2.6
The pump's maximum shaft power shall be determined by considering the following factors:
1 The requirements for shaft power under various working conditions within the operation range.
2 The influence of sediment content on the shaft power.
2.2.7
The setting elevation of pump shall meet the following requirements,and leave the appropriate safety margin:
1 At the lowest operating water level of the inlet pool,the minimum submergence depth to the reference level of axial flow pump or mixed flow pump shall exceed 0.5m.
2 The requirements of the allowable suction vacuum height or required net positive suction head (NPSHr) in different working conditions shall be met.The allowable vacuum suction height or NPSHr of the pump shall be amended if pumping from sediment-laden water source.
2.2.8
The design heads of the parallel running pumps shall be almost the same.The number of the parallel sets shall be appropriately reduced while pumping from sediment-laden water source.
2.2.9
The sediment abrasion resistance measures shall be con sidered when pumping from sediment-laden water source.The anti-corrosion measures shall be considered when pumping from a corrosive source.The pump structure shall be easy to repair and replace.
2.2.10
The flow among cascade pumping stations shall be bal anced.The adjustment and control measures such as storage regulation,combination of small and large-sized pumps,variable speed regulation,variable angle operation,etc.may be adopted when the flow is imbalanced.