Centrifugal Pump, Its working, advantages, and disadvantages
- What is Centrifugal Pump: A Centrifugal pump is a device used to lift fluid from lower to higher levels by the mean of centrifugal force acting inside the pump. Centrifugal pump is quite suitable for liquid, slurry, and suspension with solid as well.
- “A Pump is a device that is used to convert mechanical energy into hydraulic energy with the help of an external source”.
- Working Principle of centrifugal Pump: Centrifugal pumps work on the principle of centrifugal force which increases the kinetic energy of fluid and then converts it into pressure energy which is required to pump the fluid from a certain level (Suction) to the destination level (discharge).
- Important terms related to the construction of centrifugal pumps: Centrifugal pump parts and their description is below mentioned:
- Suction Port: Opening through which fluid liquid is present at the suction level and travels to the eye of the impeller due to its rotation.
- Discharge port: after reduction in pressure, Opening through which fluid is moved to the destination level.
- Impeller: Impeller is a circular construction that includes blades or vanes within it. The number of blades is in series to achieve high speed (RPM). The impeller is mounted over the shaft which is connected by a coupling connected to the motor.
- Types of impellers: Impellers are generally of three types which are the following:
- Open impeller: Blades of the open impeller is aligned to the central hub. An open impeller is suited for fluid containing suspended solids. Suitable for viscous media as well.
- Closed impeller: Closed impeller blades are held between two support plates (Base & crown plate). The semi-open impeller is efficient in operation & suitable for fluid do not contain suspended particles. Closed impellers are the most efficient impeller in comparison with other types.
- Semi-Open impeller: semi-open impeller consist only of the base plate, the crown plate is unavailable. This type of impeller is suited for liquid containing the minimum amount of solid & dirt particles. Suitable for viscous media as well.
- Casing: Casing portion in which the impeller rotates. It acts as an outer cover for the impeller. The casing is an airtight chamber (not permit the passing of air in and out).
- The construction of the casing is designed in such a way consisting of a suction inlet & discharge outlet path. This casing provided a path. The function of this path is to convert the kinetic energy generated by the impeller into pressure energy.
- Type of Casing: Generally there are two types of casing available:
- Volute type casing
- Diffuser type casing
- Note: Impeller may be single suction or double suction type which means liquid can enter from one side and in the double suction type liquid can enter from both sides of the impeller.
Important technical terms of centrifugal pumps: Centrifugal pump parts and their description is below mentioned:
Cavitation: Vapor pressure of the liquid is the pressure at a given temperature liquid is converted into vapor. Cavitation will take place when the pressure in the suction line falls below the vapor pressure of the liquid, due to this some portion of the liquid flashes into the vapor. When cavitation takes place to pump is not able to pump the liquid.
Impacts of Cavitation: Cavitation causes vibration or increased noise inside the pump. Mechanical damage is also caused by cavitation as vapor bubble collapse.
- NPSH (Net positive suction head): To avoid cavitation pump suction point pressure must be higher than the liquid vapor pressure. NPSH will be specifically mentioned by the pump manufacturer. NPSH is typically the sum of Velocity & Pressure head.
- Priming: Priming is the operation in which air present inside of the pump is removed from the suction line and casing. Priming is to be done with taken care of and before (prior) to operating the pump. Presence of air cause air binding inside the pump. Priming is to be done with a liquid that is about to be pumped.
Impacts of priming: if pump priming is not done, the suction pressure created by the pump is not sufficient enough to deliver the liquid. The pump is unable to deliver the fluid at discharge which makes the pump is running in a dry run. Overheating and mechanical failure of the pump.
- Working of Centrifugal Pump: In a centrifugal pump, Electrical energy from an external source is provided to the motor which is transferred to the shaft. Due to the electrical supply impeller tends to rotate within the stationary casing.
The impeller contains blades that rotate at high speed (RPM) to produce a reduction in pressure at the eye of the impeller helps to bring water toward the impeller from the suction pipe. Casing construction has a smaller suction line which increases the kinetic energy of fluid (i.e. reduction in surface area increases the kinetic energy and surface area directly proportional to the pressure energy of the fluid). The main purpose of the high-speed rotation is to increase the kinetic energy of the fluid and convert it into pressure energy passing through the leaving blade tips.
Coming Liquid into blade tips passed towards the volute chamber of the pump construction. Volute casing at the discharge line has a greater surface area in comparison to the suction line (i.e. increase in the surface area reduces the kinetic energy and increases the pressure energy of the fluid). As it passes through the volute chamber, finally passed through the pump discharge outlet.
- Applications of Centrifugal pumps: Centrifugal pumps are widely used in domestic & industrial process applications.
- Submersible pumps for waste supply in domestic requirements.
- Oil & Gas industry
- Food & Beverage
- Advantages of centrifugal Pumps:
- Simple design
- Low-cost & effective
- Capable to operate at high speed which means higher the speed size of the pump is small (Plot plan area for installation of a centrifugal pump is not an issue in the case of the centrifugal pump).
- Suitable for a variety of fluids (i.e. Liquid, slurry, etc.)
- Low maintenance cost in comparison to the other types
- Suitable for fluid containing solid particles in a high proportion
- Disadvantages of centrifugal Pumps:
- Operate at low efficiency (60 – 65%).
- A self-priming function is not available.
- Do not able to handle viscous fluid efficiently.
- NRV is required for either suction or discharge side due to conditions arising in which when the pump is stopped, fluid gets back to the reservoir tank.