Structural Details of Vertical Multistage Centrifugal Pumps
The vertical layout not only saves floor space but also simplifies installation (suitable for narrow spaces). Its core structure consists of a vertical pump shaft, multi-stage impellers, segmented pump casing, and auxiliary components. Below is a detailed explanation of key parts:
1 Overall Structural Features
Unlike horizontal centrifugal pumps, vertical multistage pumps have their pump shaft arranged vertically. The impellers are stacked along the shaft (typically 2–10 stages, depending on pressure requirements), and the pump casing is often of a segmented (radial split) structure—this design allows easy disassembly for maintenance and ensures uniform pressure distribution across stages.
2 Key Components & Their Functions
(1) Pump Casing
• Types: Two main structures are used:
o Radial split casing (segmented casing): Composed of multiple segments (e.g., suction segment, middle segment, discharge segment) connected by bolts. It is ideal for high-pressure multistage pumps, as the segmented design withstands high internal pressure without deformation.
o Axial split casing: Rarely used in vertical multistage models, as it is less suitable for stacked impeller layouts.
• Core Role: The inner cavity of the casing is equipped with spiral flow channels or diffusers. It collects the liquid discharged from each impeller, converts velocity energy to pressure energy, and guides the liquid to the next-stage impeller or the pump outlet. Additionally, the casing bears all operating pressures (up to 1.6–10 MPa for medium-high pressure models) and thermal loads from the liquid.
(2) Impellers
• Structure Types: Three common designs, each for specific application scenarios:
o Closed impellers: Consist of blades, a front cover plate, and a rear cover plate. They have high efficiency (typically 75%–90%) and are suitable for clean liquids (e.g., tap water, pure water), as the cover plates prevent liquid leakage and reduce energy loss.
o Semi-open impellers: Have blades and a rear cover plate (no front cover). They are used for liquids with small impurities (e.g., slightly turbid water) and have moderate efficiency (65%–80%).
o Open impellers: Only have blades (no cover plates). They are low-efficiency (50%–70%) but easy to clean, making them suitable for liquids with fibrous or granular impurities (e.g., weakly polluted industrial wastewater).
• Multistage Design: Multiple impellers are fixed on the same pump shaft in series. Each stage increases the liquid pressure by 0.2–0.5 MPa, enabling the pump to achieve the required outlet pressure (e.g., 5-stage impellers can reach 1.0–2.5 MPa).
(3) Sealing Ring (Wear Ring)
• Installation Position: Inlaid on the inner wall of the pump casing (at the impeller inlet) and the outer edge of the impeller’s front/rear cover plates.
• Function: Creates a small radial gap (0.1–0.5 mm) between the impeller and the casing to prevent internal leakage (high-pressure liquid at the impeller outlet flowing back to the low-pressure inlet) and reduce efficiency loss. Made of wear-resistant materials (e.g., cast iron, stainless steel), it can be replaced after wear to extend the pump’s service life.
(4) Pump Shaft & Bearings
• Pump Shaft: Typically made of 45# carbon steel or 304 stainless steel (for corrosion resistance). It transmits torque from the motor to the impellers and ensures coaxial rotation of multiple impellers.
• Bearings: Two types are used based on pump size and load:
o Rolling bearings: For small-to-medium pumps (flow rate < 100 m³/h), lubricated with grease, requiring low maintenance.
o Plain bearings: For large pumps (flow rate > 100 m³/h), lubricated with the conveyed liquid (water-lubricated) to reduce friction and heat generation.
(5) Shaft Seals
• Purpose: Prevent external leakage (liquid in the pump leaking to the environment) and air ingress (which would destroy the vacuum at the inlet).
• Common Types:
o Mechanical seals: Consist of a stationary ring and a rotating ring. They have low leakage (≤ 5 mL/h), long service life (1–2 years), and are suitable for high-pressure (≥ 1.0 MPa) or high-temperature (≤ 80℃) conditions—widely used in municipal and industrial applications.
o Packing seals (gland seals): Made of flexible packing (e.g., PTFE, asbestos-free materials). They are low-cost and easy to replace but have higher leakage (≤ 100 mL/h) and require regular adjustment of the gland pressure—suitable for low-pressure (≤ 0.6 MPa) scenarios (e.g., residential water supply).
• Design Feature: Most vertical multistage pumps are compatible with both seal types, allowing customization based on user needs.
(6) Auxiliary Components
• Bottom valve: Installed at the end of the suction pipe to prevent liquid backflow when the pump is shut down (avoids re-priming).
• Control valve: Installed on the discharge pipe to regulate flow and pressure (prevents overloading the motor during startup).
• Inlet/outlet flanges: Standardized (e.g., PN1.0/1.6 MPa) for easy connection to pipelines.
To recap, the above has detailed the key structural components of vertical multistage centrifugal pumps, aiming to offer clear insights for your understanding. As a professional manufacturer of such pumps, Rondos provides high-performance, reliable products with strict quality control and tailored technical support. For more in-depth resources or one-on-one consulting, please visit our official website.