7 Workflow Editing
The characteristic curve of a centrifugal pump is an inherent property of the pump itself, unrelated to external operating conditions. However, once the pump is installed in a specific pipeline system for operation, its actual working conditions are not only related to the characteristics of the pump itself but also depend on the working characteristics of the pipeline. Therefore, to select and utilize centrifugal pumps effectively, it is also necessary to consider the characteristics of the pipeline.
When transporting liquids through a specific pipeline, the required pressure head (He) of the pipeline varies with the square of the flow rate (Qe). Plotting this relationship on a graph paper yields the corresponding pipeline characteristic curve.
If the characteristic curve of the centrifugal pump and the characteristic curve of the pipeline are plotted on the same coordinate paper, the intersection point of the two lines, M, is called the pump's operating point. When selecting a pump, the flow rate and head at the operating point should meet both the requirements of the pipeline system and exactly match what the centrifugal pump can provide, i.e., Q=Qe, H=He.

Maintain
3.1 Analysis of Centrifugal Pump Mechanical Seal Failure
The shutdown of centrifugal pumps is primarily caused by the failure of mechanical seals. The manifestations of failure are usually leakage, and the causes of leakage include the following:

Basic Structure
The basic structure of a centrifugal pump consists of eight main components: impeller, pump casing, pump cover, water shield, pump shaft, bearings, sealing ring, stuffing box, and axial force balancing device.
1. The impeller is the core component of the centrifugal pump, featuring high speed and great output power.
2. The pump body, also known as the pump casing, is the main component of the water pump. It serves as a support and fixation, and is connected to the bracket with mounted bearings.
3. The role of the pump shaft is to connect the motor via a coupling, transferring the motor's torque to the impeller, making it the main component for transmitting mechanical energy.
4. Sealing rings are also known as leak-reduction rings.
5. The stuffing box is mainly composed of packing material, which prevents the flow of water inside the pump from escaping and also keeps outside air from entering the pump. Always maintain a vacuum within the pump! When friction between the pump shaft and packing generates heat, it is necessary to inject water into the stuffing box through the water seal tube to cool the packing!
6. Axial force balancing device – During the operation of centrifugal pumps, as the fluid enters the impeller at low pressure and exits at high pressure, it creates unequal pressure on both sides of the impeller, resulting in an axial thrust towards the direction. This can cause the rotor to move axially, leading to wear and vibration. Therefore, an axial thrust bearing should be installed to balance the axial forces.
Types
I. Categorized by the number of impellers
Multistage centrifugal pump
Multistage Centrifugal Pump
Single-stage pump: A pump with only one impeller on the pump shaft.
2. Multi-stage pump: A pump with two or more impellers on the pump shaft, where the total head of the pump is the sum of the head generated by each impeller.
II. Categorized by Working Pressure
1. Low-pressure pump: Pressure less than 100 meters of water column.
2. Medium-pressure pump: Pressure ranging from 100 to 650 meters of water column.
3. High-pressure pump: Pressure over 650 meters of water column.
Section 3: Categorized by the Impeller Inlet Type
1. Single-sided suction pump: Also known as a single-suction pump, featuring only one intake port on the impeller.
2. Double Suction Pump: Also known as a double suction pump, featuring an intake on both sides of the impeller. It has twice the flow rate of a single suction pump and can be likened to two single suction pump impellers placed back-to-back.
Four: Categorized by pump housing assembly
Horizontal split case pump: A pump with a split case that is open on the horizontal plane through the axis line.
2. Vertical combined face pump: The combined face is perpendicular to the axis line.
V. By Pump Shaft Position
Horizontal Pump: Pump shaft is in a horizontal position.
Horizontal Pump
Horizontal Pump
2. Vertical Pump: The pump shaft is in a vertical position.
Six, classified by impeller outlet type
1. Suction pump: After water exits the impeller, it directly enters the pump casing, which has a helical shape.
2. Guide vane pump: After water exits the impeller, it enters the guide vanes set outside, then flows into the next stage or into the outlet pipe.

Leakage of the static and dynamic sealing surface, mainly caused by: insufficient flatness and roughness of the faces; surface scratches; particles between the faces preventing even operation; incorrect installation and method.

② Reasons for leakage in compensation ring seals mainly include: deformation of the pressure cover, uneven preload; incorrect installation; seal ring quality not meeting standards; incorrect seal ring selection.
Actual usage shows that the areas with frequent failure of sealing elements are the end faces of the dynamic and static rings. Cracking on the end faces of the centrifugal pump's dynamic and static rings is a common failure phenomenon, mainly due to:
①During installation, the gap between the sealing surfaces is too large, leaving insufficient time for the flushing fluid to remove the heat generated by the friction components. The flushing fluid leaks out through the gap, causing the end face to overheat and become damaged.
②The liquid medium vaporizes and expands, causing the two ends to separate due to the vaporization expansion force. When the two sealed surfaces are pressed tightly together, the lubricating film is destroyed, leading to excessive overheating of the end surface.
③ Poor lubricity of the liquid medium, combined with overload operation pressure, results in the two sealing surfaces not tracking rotation synchronously. For instance, a high-speed pump with a speed of 20,445 rpm and a central diameter of the sealing surface at 7 cm, its linear velocity reaches up to 75 m/s upon operation. If one sealing surface lags behind and cannot keep up with the rotation, the instantaneous high temperature can cause damage to the sealing surface.
④ Sealed flush liquid orifice plate or filter screen blockage, leading to insufficient water volume and failure of the mechanical seal.