Knowledge of Multistage Centrifugal Pump

What is a Multistage Centrifugal Pump?

A multistage centrifugal pump is a collection of more than two pumps. In the structure of the fluid channel, the medium pressure relief port of the first stage communicates with the inlet of the second stage, and the medium pressure relief port of the second stage is connected to the third stage. The inlets are connected to each other, and such a series-connected mechanism forms a multistage pump. The significance of the multistage centrifugal pumps are used to increase the set pressure.

How to assemble a multistage centrifugal pump

When assembling a multistage centrifugal pump, all bolts and nut threads must be coated with lead powder oil. After assembling the last stage of the impeller, the axial distance between the hub and the two ends of the balance disc hub should be measured, and the axial size of the stop sleeve in between is determined according to this axial distance. The sum of the axial clearance between the stop sleeve and the impeller hub, the stop sleeve and the balance disc hub is 0.30~0.50mm. Because the parts on the shaft of the impeller and other shafts are first affected by the medium with higher temperature during the initial start-up of the multistage centrifugal pump, and the shaft is affected by heat later, their expansion has a time difference. The axial clearance of 0.3~0.5mm is left to prevent the impeller, balance disc, etc. from expanding first and die against each other, which may cause greater tensile stress on the pump shaft.

The long stem bolt can only be tightened slightly at the beginning of assembly. After the entire multistage centrifugal pump is in place on site, the long rod bolts are tightened according to the recorded data. The tightening must be done symmetrically, otherwise it will cause poor sealing between the segments.

When installing the balance disc seat pressure ring on the multistage centrifugal pump, align a notch on it with the connection of the balance water pipe. Otherwise, the balance water pipe will be blocked and the entire axial balance device will lose its function.

Preparation work before starting the multistage centrifugal pump

First, Check some places before starting the multistage centrifugal pump.

1. Whether the name, model, main performance and quantity of lubricating oil of multistage pump meet the requirements of technical documents;

2. Whether the bearing lubrication system, sealing system and cooling system are intact, and whether the oil circuit and water circuit of the bearing are unblocked;

3. Turn the rotor of the pump for 1 to 2 revolutions, and check whether the rotor has friction or jamming;

4. Whether there is any debris that hinders rotation near the coupling or belt guard;

5. Whether the foundation bolts of the multistage pump, bearing seat, and motor are loose;

6. The valves or accessories of the multistage pump working system should be in the position with the least load when the pump is running, and the outlet regulating valve should be closed;

7. Start the multistage pump to see if its impeller rotation is consistent with the design rotation. If it is inconsistent, the impeller must be completely stopped and the motor wiring can be adjusted before restarting.

Secondly, Check the multistage centrifugal pump for water filling. Before starting the water pump, the pump casing and suction pipe must be filled with water first. This is because the multistage pump suction vacuum cannot be formed and maintained in the presence of air.

Thirdly, Multi-stage centrifugal pump heating pump. Pumps that transport high-temperature liquids, such as boiler feed pumps in power plants, must warm up the pumps before starting the multi-stage centrifugal pumps. This is because when the feed water pump is started, the high temperature feed water flows through the pump, causing the temperature of the pump body to rise quickly from normal temperature to 100-200°C, which will cause the temperature difference between the inside and outside of the pump and the parts. Heat transfer time and appropriate measures to control temperature rise will cause uneven expansion throughout the pump, causing deformation, wear, vibration, and bearing shaft accidents of all parts of the pump body.

How to clean the multistage centrifugal pump

Multistage centrifugal pump is a very common type of pump. However, it is very important to clean it regularly. The cleaning steps are as following:

1. When the bearings of the multistage centrifugal pump are removed for inspection, the appearance record should be recorded by photography and other methods. In addition, confirm the amount of remaining lubricant and sample the lubricant before cleaning the multistage pump bearings.

2. When fine washing, slowly rotate the water pump bearing in the oil, which must be carried out carefully.

3. For rough washing, use a brush to remove grease or adhesions in oil. At this time, if the water pump bearing is rotated in oil, be careful that the rolling surface may be damaged due to foreign matter.

4. The commonly used cleaning agents are neutral non-water-containing diesel or kerosene, and sometimes warm lye etc. are used as needed. No matter which cleaning agent is used, it must be filtered frequently to keep it clean.

5. The bearings of the horizontal centrifugal pump are cleaned into rough washing and fine washing, and a metal grid can be placed at the bottom of the container.

6. After cleaning, immediately apply anti-rust oil or anti-rust grease on the bearings of multistage centrifugal pumps.

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