Multistage pumps are similar in design to centrifugal pumps in that multiple impellers rotate around a shaft, enabling the pump to reach higher pressures than using just one impeller.
When the impeller diameter reaches a certain level, the friction on the impeller side increases and the pump efficiency decreases, so the pressure that a single impeller can generate is limited. This meant that multiple impellers had to be added along a single axis to generate high pressures while maintaining high efficiency.
The impeller of this design is mounted in an annular section along the shaft. Each annular section consists of an impeller with a suction casing on one side and an impeller with a discharge casing/diffuser on the other.
The impeller draws fluid through the suction casing into the outside of the impeller, and then exits through the discharge casing, repeatedly entering different ring segments until the fluid leaves the outlet.
The annular portions are held together by tie bolts extending along the housing. Internal design depends on the shaft seal and/or bearing at one end of the pump, depending on the job and application.
Increasing the number of impeller stages does not change the flow, but the total lift and shaft power increase proportionally to the number of stages. Each stage consists of an impeller and a diffuser.
Models can be built vertically or horizontally, depending on whether a space-saving design is required. It can also stay in place without removing the motor.
The multistage design of the pump is also used in a submersible pump design called a borehole pump. In this case, water must be pumped at high pressure to extract water from deep wells or to supply water from the sea surface to offshore platforms. Immersion pumps can also be equipped with multiple impellers to provide high pressure from deep wells.
There are several reasons to use such devices.
1. If a high-lift centrifugal pump is required but exceeds the working range of the single-stage centrifugal pump, the maximum discharge pressure of the single-stage centrifugal pump is usually 150M, and the multi-impeller design is 1000M.
Some applications require high discharge pressures, such as supplying domestic water to the upper floors of skyscrapers. This can mean long flow paths, high friction losses commonly found in pressurized applications, or filtration processes that require filtering of low viscosity liquids. It passes through fine filters such as reverse osmosis membranes.
2. When a cost-effective high-pressure cleaning solution is required, a more efficient multi-stage design can be used. This is because the impeller is not only small, but also efficient at full impeller size and low rpm.
The single-stage design is trimmed to the operating point with a large gap between the impeller edge and the casing, resulting in low efficiency.
What is Vertical Multistage Centrifugal Pump
A vertical multistage centrifugal pump is a high-efficiency pump that can be used for a variety of applications. It is a durable and reliable pump that is designed for long-term use. The pump is easy to operate and maintain, and it can be used in a wide range of operating conditions.
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