Vertical Centrifugal Pump
What is vertical centrifugal pump?
Vertical centrifugal pumps are also known as deep good turbine pumps. The vertical centrifugal pumps are vertical axis mixed flow centrifugal pumps which include stages of stationary bowls and rotating impellers that process guide vanes. Vertical centrifugal pumps have a complicated design and are more expensive. The design of the pressure head for a vertical centrifugal pump depends mainly on impeller length and rotation speed. A vertical centrifugal pump manufactured with a single impeller cannot be that powerful. An impeller can be achieved by adding extra stage and bowl assemblies.
Figure: Vertical centrifugal pumps.
How do Vertical centrifugal pumps work?
Vertical centrifugal pumps work by using an electric motor or using a diesel engine. The end of the vertical centrifugal pump has at least one impeller attached to the shaft that is used to direct the fluid into the diffuser casing (bowl). There are multi-stage configurations of vertical centrifugal pumps that use multiple impellers on one shaft to create higher pressure enough to lift fluid through a large head. A vertical centrifugal pump work when fluid enters the pump at the bottom via a bell-shaped component known as a suction bell. From the suction bell the fluid moves to the first stage impeller where its velocity is increased. The fluid then enters into the diffuser bowl where the high velocity is converted into pressure energy. The bowl also helps to direct the fluid to the next impeller and the process continues for all other impeller stages of the pump. When the fluid exits the last diffuser bowl, it proceeds through a long vertical pipe rising into the well bore to the surface. The rotating shaft in the pipe column has sleeve bushing supports at three feet intervals mounted in the column and gets lubricated by the fluid moving through them. The pump discharge head is at the surface and it allows change of direction to the flow to the discharge pipe. The prime mover which is either a motor or diesel engine is attached above the discharge head.
Types of vertical centrifugal pumps
There are different types of vertical centrifugal pumps as discussed below.
Barrel vertical centrifugal pump
A barrel vertical centrifugal pump is a pump that works while fitted on top of a drum opening with a narrow tube where a vertical shaft is housed. This pump has a small electric motor that provides power through a switch. This pump is portable and is meant for efficient and safe transport of fluids from drums, storage tanks, or barrels.
Figure: Vertical centrifugal barrel pump.
Vertical inline centrifugal pump
A vertical inline centrifugal pump is a single-stage dynamic pump meant for vertical installation. This pump has its delivery and suction inline so that it can afford a smooth flow of fluid. This pump is ideal for conveying low viscosity fluids at a wide range of heads and flow rates. This type of pump is used in various applications among them pumping chemicals and water.
Figure: Vertical inline centrifugal pump
Vertical column centrifugal pumps
Vertical column centrifugal pumps are also known as immersion pumps. These pumps are used in pits or tanks instead of pumps that need priming or flooded suction. These pumps are immersed vertically in the fluid being pumped but the motor is separated from the fluid by use of a long vertical shaft. Thus the electric motor is kept well above the fluid being pumped and it gets connected to the pump via a vertical shaft where impellers are mounted. The impellers are immersed in the fluid. These pumps are ideal for pumping fluid from an underground well, sump, tank, or reservoir. The vertical column centrifugal pump manufacturers make this pump able to handle flammable fluids as well as fluid at high temperatures.
Figure: Vertical column centrifugal pump.
Submersible vertical centrifugal pumps
This is a single-stage pump. It is a radially split, vertical, seal-less pump fitted with a channel impeller or radial impeller. This type of pump is used in various applications such as automatic water drainage from pits such as sewage, transfer of chemically aggressive fluids, heat transfer fluids, tanks transporting condensate among others.
Figure: Submersible vertical centrifugal pump.
Deep well vertical centrifugal pumps
Deep well vertical centrifugal pumps are similar to submersible vertical centrifugal pumps. This type of pump is used to pump fluid from deep ground levels. This type of pump has a shaft that extends from deep grounds to the ground surface. The pump is coupled with a dry motor. This type of pump is a multistage pump with mixed flow impellers. A deep well vertical centrifugal pump can be extended in shaft sections to go even deeper. The large lengths are created by standard extension sets of intermediate shafts and intermediate couplings, bearing spider and column pipe.
Figure: Deep well vertical centrifugal pump
Vertical centrifugal can Pumps
This is a vertical centrifugal pump with multiple impellers. It is a short-set line shaft pump that has suction piping connected to the sleeve or an inlet allowing the can to create a pump reservoir. This pump is suitable for closed-loop boost. A vertical centrifugal can pump is good for site locations where there is suction piping rather than a reservoir or existing pump.
Figure: Vertical centrifugal can pump.
Selection of vertical centrifugal pump
The working of a vertical centrifugal pump is affected by several factors which are a type of fluid, available space, temperature and pressure, and net positive suction head (NPSH).
- Available space. The vertical centrifugal pump should be selected based on the availability of the space. A vertical centrifugal pump needs less floor space but requires more headroom.
- Transmission of the fluid. The vertical centrifugal pumps are often meant for lifting fluid from deeper levels unlike other pumps such as horizontal centrifugal pumps.
- NPSH required. A vertical centrifugal pump can provide more NPSH, unlike other pumps.
- Temperature and pressure of the fluid. A vertical centrifugal pump can handle more pressure and temperature relative to a horizontal centrifugal pump.
Advantages of vertical centrifugal pumps
- Vertical centrifugal pumps need less floor space for installation.
- Vertical centrifugal pumps have fewer wearing parts making them economical for use.
- These pumps are suitable for pumping fluids with high pressure and temperature.
- Vertical centrifugal pumps have the flow rate stable, even, and easier to adjust.
Disadvantages of vertical centrifugal pumps
- Vertical centrifugal pumps have their performance-sensitive to changing fluid viscosity.
- Due to the vertical orientation of vertical centrifugal pumps, they need a large headroom.
- Vertical centrifugal pumps find it hard to pump fluids with dissolved gases. When this happened the pump’s mechanical seal can be damaged.
- The overhung design of the pump, shaft, and motor results in some challenges due to axial thrust especially when high pressure is involved.
- In a vertical centrifugal pump with several stages, there will be a need for barrel and pit resulting in extra cost.
Applications of vertical centrifugal pumps
- Vertical centrifugal pumps are used to boost pipeline pressure.
- Vertical centrifugal pumps are used in refinery blending and product transfer processes.
- These pumps are used in chemical transfer
- They are used in cryogenic piping
- Vertical centrifugal pumps are used in piping boiler feed water
- These pumps are used in piping condensate
- They are also used to pump seawater
- Vertical centrifugal pumps are used to pump light hydrocarbons
- Vertical centrifugal pumps are used to transfer liquefied natural gas
Troubleshooting of vertical centrifugal pumps
The pump has insufficient pressure
The probable causes of this problem and their solutions are:
- There is very low speed. In this case, the motor needs to be checked for speed, hp, voltage, and if necessary replace that motor.
- The impeller is loose. The pumps need to be pulled and the impeller tightened.
- Improper impeller trim. The pump needs to be removed and the impeller replaced.
- Cavitation. What to do in this case is to lower the temperature of the fluid being pumped, increase submergence of the pump, check the sump complies with the hydraulic institute recommendations, if necessary the sump can be redesigned.
- Leakage in the discharge pipe. In this case, the pipe sections can be changed or the leaks plugged.
- Worn outwear rings. In this case, the pump can be pulled and shaft inspected for bents, worn out rings replaced, abrasive material removed, and impeller settings adjusted according to peerless recommendations.
- Wrong rotation. When this happens, the pump needs to be checked for counterclockwise rotation as viewed on the top of the motor. The motor rotation can then be reversed if found necessary. This can be done by swapping leads in the terminal box of the motor.
There is insufficient capacity
Some of the probable causes to this problem and their solutions are:
- Very low speed. The motor needs to be checked for speed, voltage, and hp and if necessary replace the motor. The impeller is loose. The pumps need to be pulled and the impeller tightened.
- Improper impeller trim. The pump needs to be removed and the impeller replaced.
- The bowl or impeller is partially plugged. In this case, the pump needs to be disassembled, inspect it and if there are foreign materials be removed, then the pump is reassembled and the impeller set to the correct lateral settings.
The pump delivers no liquid
- The pump suction is broken. In this case, the minimum fluid level in the sump needs to be increased according to the requirements of the vertical centrifugal manufacturer.
- The pump’s suction valve is closed. In this case, the suction valve needs to be opened.
- The strainer is clogged. This problem is solved by removing the strainer and inspecting and cleaning it.
The pump is producing abnormal noise
The probable causes of the problem and the solution:
- The motor is producing noise. This could be due to pump bearings having run dry. In this case, the minimum submergence needs to be checked, and ensure that the minimum fluid level is above the first stage impeller centerline.
- Column bearing retainers are broken. This case would require removing and replacing of retainer bearing, and replacing the bearings.
- The shaft enclosing tube shaft is broken. In this case, the pump needs to be disassembled and the broken shaft or tube replaced.
Summary
Pumps are machines used to transport fluid from one place to another. One of the types of pumps is the vertical centrifugal pump. This pump as the name suggests works will be maintained in a vertical position. It is used to pump fluids from the deep underground level to the required destination. These pumps can be of a single impeller or multiple impellers. The multiple impeller vertical centrifugal pump is more powerful as the more impellers produce more power. There are several types of vertical centrifugal pumps used for transporting fluids. The vertical centrifugal pumps are applicable when transporting fluids vertically. Such applications of vertical centrifugal pumps include pumping water from boreholes, pumping sewage from underground levels, pumping chemicals, among others.