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**1 Introduction**
The Shanghai Huangpu Jiangyuan Water Plant consists of two raw water pumping stations, Linjiang Pumping Station and Yanqiao Pumping Station, both constructed in 1987. Each station is equipped with six large vertical concrete volute mixed-flow pumps, designed to ensure the delivery of high-quality raw water from the upper reaches of the Huangpu River to the respective water treatment plants in Shanghai. These two pumping stations have a combined daily capacity of 3.5 million tons.
From their commissioning in 1987 until 1997, the pumping stations gradually faced several operational challenges. As a result, Changsha Pump Factory Co., Ltd. was commissioned by the plant owners and collaborated with local authorities in Shanghai to carry out a comprehensive renovation project, which required an investment of nearly 30 million yuan. The transformation took place between 1998 and 2001, during which 12 cement elbow-inlet volute mixed-flow pumps were replaced with wet-pit sink suction diagonal-flow pumps. This upgrade significantly improved the efficiency and reliability of the pump systems, leading to substantial energy savings and economic benefits.
**2 Pump Station Basic Situation**
Both Linjiang and Yanqiao Pumping Stations originally used 1800HLWB-12 vertical mixed-flow pumps, as shown in Figure 1. The design features of these pumps include a cement elbow suction runner, a cement volute mixed-flow structure, semi-adjustable and semi-open impellers, an embedded impeller chamber within a cement matrix, a floating ring shaft seal, and a rigid motor coupling. The axial thrust is supported by the motor's thrust bearing. The original performance parameters are: flow rate Q = 7.792 m³/s, head H = 12.2 m, speed n = 300 rpm, efficiency η = 87.2%, and motor power of 1600 kW.
**3 Main Problems of the Original Pump Station**
(1) **Low Operating Efficiency**: Field measurements showed that the pump efficiency ranged from 60% to 70%. The primary cause was the gap between the vanes and the impeller chamber not meeting the design requirements (0.8–1.0 mm).
(2) **Poor Sealing Reliability**: The original floating ring seal had unstable performance, requiring a submersible pump to be installed on the pump cover and a dedicated inspector to monitor for leaks.
(3) **Short Maintenance Cycle**: After about one year of operation, the pumps often experienced severe vibration, significant leakage, and reduced efficiency, necessitating frequent maintenance.
(4) **Blade Cavitation Damage**: Annual overhauls revealed cavitation damage on the impeller blades, requiring time-consuming repairs and resulting in poor working conditions for maintenance personnel.
**4 Transformation Program and Implementation**
To address the key issues of the original pumping station, a complete redesign of the pump performance, structure, and suction system was carried out. The new system involved replacing the original pumps with wet-pit sink suction vertical diagonal-flow pumps while keeping the original motors unchanged. The motor mounting base was repositioned, and anchor bolts were rearranged. The transformed pump room structure and inlet channel layout are illustrated in Figure 2.
Based on past operational data and pump characteristics, the new pump was designed with the following parameters: flow Q = 9 m³/s, head H = 12 m, speed n = 300 rpm, and specific speed ns = 3.65nQ¹/²/H³/ⴠ≈ 510. A L500 hydraulic model was used for the conversion, resulting in the new pump model 88LKSE-18J. The theoretical performance curve is shown in Figure 3 (double-dotted line), and the actual test results (solid line) met all design specifications.
**5 Structural Characteristics of the Pump After Transformation**
Figure 4 illustrates the modified vertical diagonal-flow pump. Compared to the original design, the new structure has the following improvements:
(1) Replaced the original cement-type mixed-flow pump with an all-metal guide vane mixed-flow pump.
(2) The impeller chamber is no longer embedded in cement; instead, it is designed with conical surfaces, allowing for easier extraction and maintenance.
(3) The cavitation standard elevation was lowered by 1.55 m, increasing the net positive suction head (NPSH) and reducing cavitation risk.
(4) The impeller length was reduced from 1.1 m to 0.6 m, improving the stress distribution on the lower bearing and extending its lifespan.
(5) A locking nut was added between the pump and motor coupling, enabling easy adjustment of the impeller position to maintain optimal clearance.
(6) The new pump uses a general packing seal, with minimal leakage that can be directed into the sump, eliminating the need for a dedicated inspection post.
(7) The rotor parts can be removed from the top, allowing maintenance to be performed at the motor base level without entering the pump chamber, improving safety and working conditions.
**6 Conclusion**
This technological upgrade, initiated in 1998 and completed by 2001, has been in operation for more than four years. Field tests show significant improvements compared to the original system:
(1) The pump operating efficiency reached up to 88%, saving approximately 9.6 million yuan annually in electricity costs. At a daily capacity of 3.5 million tons, annual savings could exceed 14 million yuan, with a return on investment within three years.
(2) Major overhauls are now required every 3–4 years, tripling or quadrupling the maintenance interval and reducing labor and costs.
(3) Vibration levels are below 5 mm/s, and shaft sealing leakage is normal, enhancing operational safety and reliability.
(4) No cavitation damage has been observed on the impeller blades after four years of operation.
(5) The working environment and workload for operators and maintenance staff have significantly improved, contributing to better overall performance and sustainability.