Centrifugal pump

The principle of operation of a centrifugal pump

The main element of a centrifugal pump is the impeller (impeller), located inside the volute casing (volute), which has blades directed in the opposite direction relative to the rotation of the wheel itself. The impeller is mounted on a shaft that is connected to the pump drive. When the unit is started, the impeller starts to rotate, and the liquid flows through the suction pipe along the axis of rotation of the wheel.

Under the action of centrifugal force, the liquid moves along the channels between the blades in the radial direction (from the center of the impeller to its periphery) into the volute of the pump casing, and then into the pump discharge pipe. On the periphery of the impeller there is a zone of increased pressure. In the center, the pressure is reduced, which ensures a constant flow of liquid into the pump.

Centrifugal pump design

A centrifugal pump consists of the following main parts:

• Suction connection
• Discharge pipe
• Volute casing (flow path of the pump)
• Impeller (impeller)
• Shaft seal
• Crankcase pump

Classification of centrifugal pumps

Centrifugal pumps can be classified according to the design of its main elements, the type of installation and purpose.

By the location of the pump nozzles

• Pump "in - line" type. With this type of pump, the suction and discharge nozzles are in line with each other. The pumped liquid flows through the pump. The pump is installed in straight pipe sections.

• • Cantilever pumps. The liquid enters the center of the impeller (impeller). The branch pipes are located at 90 ° C relative to each other.
  Cantilever pumps

  By the number of pump stages

  • Single stage pump. Pump with one impeller on the shaft. These pumps are used for applications where a high head is not required. The maximum head for single - stage pumps usually does not exceed. Single stage pump
  • A multistage pump has more than one series - connected wheels on the shaft. This type of pump is used to provide a high head at a relatively low flow rate. The high head is created by the sum of the heads generated by each individual wheel. The pumped liquid passes sequentially from one stage to another.
• Multistage pump

  Shaft seal type

  Various sealing systems are used to protect the pumped liquid from entering the environment and the mechanical part of the centrifugal pump. By the type of system used, the pumps can be divided into:

  • Gland Seal Centrifugal Pumps (Gland Seal Link)
  • Centrifugal pumps with mechanical seal (single or double) (link to mechanical seal)
  • Magnetic Drive Centrifugal Pumps (Magnetic Drive Link)
  • Centrifugal pumps hermetic wet rotor (wet rotor link)
  • Centrifugal pumps with dynamic seal (link to dynamic seal)

  By the type of connection with the electric motor

  Centrifugal pumps are also divided according to the type of connection between the hydraulic part of the pump and the electric motor. The types are distinguished:

  • Pump with coupler. An elastic coupling is an element that allows you to connect the shaft of the electric motor and the shaft on which the impeller is mounted. For this, both a conventional coupling and a coupling with an intermediate element are used. The use of an intermediate piece prevents the motor from being disconnected during pump maintenance, for example when replacing the mechanical seal.

    Conventional coupling

    Spacer coupling

  • Monoblock pump. In this type of pump, the impeller is mounted either directly on the extended shaft of the electric motor, or a fixed permanent blind coupling is used to connect the motor shaft and the pump. Blind coupling centrifugal pump

    By appointment

    Due to its design possibilities, the purpose of a centrifugal pump can be very different. According to this indicator, the following types of centrifugal pumps are distinguished:

    • Drainage
    • Downhole
    • Fecal
    • Slurry
    • Food
    • Sanitary
    • Firefighters
    • Self - priming

    Material design of centrifugal pumps

    Centrifugal pumps are used in almost all industries, pumping a wide variety of liquids, from water to highly aggressive and abrasive slurries.

    Therefore, the choice of materials for the main elements of centrifugal pumps is very wide and most often it is based on the resistance of this material to the properties of the pumped liquid (link to the table of chemical resistance) and the operating conditions of the pump itself.

    The following main materials can be distinguished:

    Metal execution

    • Cast iron
    • Bronze
    • Carbon steel
    • Stainless steel
    • Duplex
    • Super duplex
    • Titanium
    • Etc

    Lined and plastic versions

    When working with highly corrosive liquids such as acids, the metal version cannot always provide the required corrosion protection. Or the use of ultra - resistant alloys can lead to a significant increase in the cost of the entire structure.

    Therefore, the use of a wide variety of plastics has become widespread, as the main material in contact with the medium in centrifugal pumps.

    Two main types can be distinguished:

    • Lined pumps. Lining is the process of applying a plastic coating to a metal pump housing. All elements in contact with the pumped medium are covered with a polymer layer, which significantly increases the corrosion resistance of the entire flow path. Modern technologies provide excellent adhesion between the coating and the body, because during casting, the polymer fills all cavities and gaps.
    • Plastic centrifugal pumps. The main elements of the pump in contact with the medium are made of solid plastic processed on special machines.

    Materials for lined and plastic pumps:

    • PP - polypropylene
    • PVDF - polyvinyldenefluoride
    • PE - polyethylene
    • PVC - polyvinyl chloride
    • PFA - perfluoroalkoxyl
    • PTFE - polytetrafluoroethylene
    • ETFE - ethylene tetrafluoroethylene (Tefzel)
    • FEP - fluoroethylenepropylene

    O - ring materials

    The following elastomers are most commonly used as O - rings in centrifugal pumps:

    • EPDM - Ethylene Propylene Rubber
    • NBR - Nitrile butadiene rubber
    • FPM / FKM / Viton - Fluoroelastomer
    • FFKM - Perfluorinated rubber

    Advantages and Disadvantages of Centrifugal Pumps

    Benefits:

    • Simple construction
    • Few moving parts, long service life
    • High efficiency
    • High performance indicators
    • Constant flow, no pulsation
    • Capacity regulation by means of a discharge throttle valve or a frequency converter

    disadvantages

    • Impossibility of "self - priming"
    • High risk of cavitation
    • Performance is highly dependent on head
    • Most effective at only one specified operating point. When regulating the flow with a frequency converter, the efficiency is reduced
    • Cannot handle multiphase fluids containing air or gas
    • When pumping abrasive liquids, possible rapid wear of the main elements due to the high rotation speed of the impeller (about 1500 rpm).
    • Cannot handle highly viscous liquids (max. 150 cSt)

    Areas of use

    Centrifugal pumps are used in almost all industries.

    The main ones are:

    Water supply and sanitation

    Water treatment plant

    Energy

    Oil and gas industry

    Chemical industry

    Pulp and paper industry

    Mining industry

    Food

    Pharmaceutical