Shandong Yineng Heavy Industry Co.,Ltd , https://www.yinengloader.com
Vertical axial flow pump characteristics, the basic structure and installation methods
Vertical axial flow pumps are a type of vane pump characterized by their high flow rate, low head, high specific speed, and energy efficiency. These pumps are compact in size, offer adjustable performance parameters, and are particularly well-suited for low-head applications. As a result, they are commonly chosen for agricultural irrigation and drainage systems, municipal water supply and wastewater treatment, and cooling water circulation in thermal power plants.
**First, the basic structure and function**
Water from the suction reservoir enters the guide vane housing through the intake bell. As the impeller rotates, it propels the water, causing it to gain energy and develop pressure. The water then flows through the pump casing and exits via the discharge elbow. The pump is connected to the motor using a rigid coupling and an intermediate shaft. The motor's bearings support the entire downward axial load of the rotor. The intermediate shaft and motor shaft are linked via a flexible coupling, allowing for smooth operation.
Axial flow pumps feature an impeller with blades, and depending on whether the blade angle can be adjusted, they are classified into three types:
- **Fixed axial flow pump**: The impeller and blades are permanently fixed and cannot be adjusted.
- **Semi-adjustable blade axial flow pump**: Blade angles can be changed only when the machine is shut down, typically in increments of 0°, ±2°, ±4°, ±6°, or ±8°.
- **Fully adjustable blade axial flow pump**: A control mechanism (mechanical or hydraulic) allows for continuous adjustment of the blade angle, either manually, electrically, or through computer control.
**Second, wet pit and dry pit installation**
Axial flow pumps, especially large ones, require precise design of the inlet passages to ensure optimal performance, such as efficiency and cavitation resistance. This must be done by a specialized design institute.
A **wet pit installation** involves submerging the pump partially or fully in the liquid being pumped, often within the suction basin. In contrast, a **dry pit installation** places the entire pump in an air-filled environment, with the water drawn in through an elbow.
**Third, pump outlet and discharge location installation**
In a **double-base installation**, the pump is mounted on a lower foundation, while the motor is installed on an upper (motor) foundation. The motor bearings support the axial force from the pump. The forces acting on each base are calculated as follows:
- Pump base force = weight of the pump casing + weight of water inside the casing – pump axial thrust
- Motor base force = weight of the motor + weight of the pump rotor + pump axial thrust
In a **single-layer foundation installation**, the pump and motor are directly connected and mounted on a single base. The pump shaft and motor shaft are joined by a rigid coupling. The total force on the single base includes the weight of the pump casing, the pump rotor, the motor, and the water inside the casing. A double-base discharge elbow may be placed between the two bases, while a single-layer foundation can be arranged as needed.
**Fourth, removable rotor design**
Most axial flow pumps have a sealed rotor and pump body assembly, which requires lifting the entire unit for maintenance. However, some designs allow for a **removable rotor structure**, enabling the rotor and guide vanes to be withdrawn from the pump casing and discharge elbow without dismantling the pipelines, reducing lifting effort and simplifying repairs.
**Fifth, lubrication and shaft protection**
For clean water at ambient temperature, water-lubricated rubber bearings are sufficient without additional protection. However, when pumping sand-laden water (such as Yellow River water) or corrosive media (like seawater), the pump shaft and guide bearings must be protected. This is typically achieved through a sealing tube that isolates the components from the fluid, while still allowing water to serve as a lubricant.