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Vertical axial flow pump characteristics, the basic structure and installation methods
Vertical axial flow pumps are a type of vane pump known for their high flow rates, low head, and high specific speed. These pumps are highly efficient, compact in size, and offer adjustable performance parameters, making them ideal for applications with low water levels. As a result, they are commonly chosen for agricultural irrigation and drainage, municipal water supply and wastewater systems, and circulating water systems in thermal power plants.
**First, the basic structure and function**
Water from the suction pool enters the pump through a bell-shaped inlet. Inside the pump casing, the impeller's vanes push the water to rotate, converting kinetic energy into pressure energy. The water then flows through the pump cylinder and exits via the discharge elbow. The pump is connected to the motor using a rigid coupling, while the intermediate shaft uses a flexible coupling. The motor bearings support the entire downward axial force of the rotor.
Axial flow pumps can be classified based on whether their blades are adjustable:
- **Fixed-blade axial flow pump**: The impeller and blades are a single, non-adjustable unit.
- **Semi-adjustable blade axial flow pump**: Blades can be adjusted when the machine is shut down, typically in fixed angles such as 0°, ±2°, ±4°, etc.
- **Fully adjustable blade axial flow pump**: Blade angles can be continuously adjusted manually, electrically, or via computer control, allowing for precise performance optimization.
**Second, wet pit and dry pit installation**
Axial flow pumps, especially large ones, require careful design of the inlet passages to ensure optimal performance, including efficiency and cavitation resistance. These designs are usually carried out by specialized engineering institutes.
A **wet pit installation** means the pump is partially or fully submerged in the liquid being pumped. In contrast, a **dry pit installation** involves the pump being completely surrounded by air, with the suction flow directed into the pump through an elbow.
**Third, pump outlet and discharge location**
In **double-base installation**, the pump is mounted on a lower foundation, while the motor is placed on an upper foundation. The motor bearings support the axial forces. The load conditions include:
- Pump base force = pump casing weight + water inside the casing – pump axial thrust
- Motor base force = motor weight + pump rotor + pump axial thrust
In **single-layer foundation installation**, the pump and motor are directly connected and mounted on a single base. The pump and motor shafts are linked by a rigid coupling. The total load on the single-layer foundation includes:
- Pump casing weight + pump rotor weight + motor weight + water in the casing
The discharge elbow between the two bases can be placed as needed, and the single-layer foundation can also be installed on top of another base if required.
**Fourth, removable rotor design**
Most axial flow pumps have a sealed, integrated rotor and pump body. However, for easier maintenance, some models feature a removable rotor structure. This allows the rotor, along with guide vanes, to be extracted without dismantling the discharge piping, reducing lifting effort and simplifying repairs.
**Fifth, lubrication and shaft protection**
For clean water at room temperature, water-lubricated rubber bearings are typically used, eliminating the need for additional shaft protection. However, when pumping sand-laden water (such as Yellow River water) or corrosive fluids (like seawater), protective sleeves are installed around the shaft and guide bearings to isolate them from the medium. Lubrication is still provided by water, ensuring smooth operation and extending the pump’s lifespan.