Centrifugal Monoblock Pump

Centrifugal Monoblock Pump


A centrifugal monoblock pump can be described as a type of pump in which the motor and the impeller are assembled within the same structure. In this pump, all the rotating components such as the impeller and the motor armature share a common shaft without coupling. The word “mono” means a single unit and the name “monoblock” implies a pump that strongly connects with a prime mover on a single structure. Monoblock pumps are strong with consistent discharge hence they are suitable for use in agricultural, civil, and industrial applications where freshwater is involved. Where reliability and cost-efficient supply are the main factors under consideration, monoblock pumps are the ones to go for.

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Parts of Monoblock centrifugal pump

The parts of a centrifugal monoblock pump are dived into rotary and stationary components

  1. A rotating component including an impeller, impeller blades, and shaft
  2. A stationary component comprising pump casing, bearing, inlet and outlet valve, suction nozzle, discharge nozzle

Pump casing

The pump casing is usually made of cast iron. The centrifugal monoblock pump casing houses the impeller and is connected to the suction and discharge nozzles. For easier dismantling and removal of the entire impeller, the pump casing is usually split in the horizontal plane and the two parts are held together using bolts and location pins.

Generally, there are two types of pump casing i.e., volute and diffusing casing, but the volute casing type is the most commonly used. The volute casing has a spiral design in which the passage of the liquid increases gradually all around the casing circumference. As a result, the fluid velocity decreases while the fluid pressure increases. On the other hand, a diffusing casing has a circular shape and it contains several guide blades that surround the impeller in the pump assembly. The guide blades increase the area of flowing water thereby decreasing the fluid velocity and increasing the pressure. The guide blades also help to ensure that the water reaching the casing from the impeller is free of shock waves. After the water passes the guide blades it flows through the surrounding casing which remains concentric with the impeller. In addition to housing the impeller, a pump casing also converts the kinetic energy into the pressure head.


The motor provides the mechanical power to run the pump impeller. The type of electric motor that is mostly used with a centrifugal monoblock pump is a completely fenced induction motor. This kind of motor is simple and compact in construction, cheap, and maintenance-free.


This is the main rotating part of the pump whose function is to provide the centrifugal force to move the fluid axially and radially. The impeller also carries the impeller blades that increase the speed of the fluid. An impeller is manufactured from close-grained cast iron or cast steel. The number of impellers i.e., equal to the pump stages. Pump manufacturers classify impellers by the direction of flow, suction type, and the constructional geometry


The purpose of the shaft is to transfer mechanical torques from the motor to the impeller during pump operation.

Inlet and outlet valves

An inlet valve helps with sucking the fluid into the pump impellers eye while the outlet valve helps to discharge fluid to the required area

Working of monoblock centrifugal pump

When the centrifugal monoblock pump is powered, the rotation of the impeller sucks fluid and sends it to the center of the impeller, also known as the impeller’s eye. As the impeller continues to rotate, the fluid is whirled outwards to the periphery due to the centrifugal force. The impeller blades increase both the energy and velocity of the fluid. When the fluid has successfully passed through the impeller area, it enters the volute casing where the high velocity is converted into pressure energy leading to an increase in the pressure of the fluid. The fluid then discharges through the outlet valve and pumps to the desired area. The shape of the volute chamber is such that the cross-section progressively decreases towards the delivery side to ensure that the conversion of energy is smooth and free of turbulence and shock. The occurrence of Shock waves and turbulence can also be eliminated through the use of diffuser vanes of appropriate shape on the inner periphery of the pump casing.

During operation, the pump must always be filled with water to prevent the occurrence of failure, which may occur if the pump dries out. However, some monoblock pumps are self-priming. Self-primed monoblock pumps usually contain a water jet or a die channel and they utilize an air-water composition to manage a complete primed condition. Some operation parameters of the pump such as speed, voltage, and voltage may be adjusted depending on the required pressure gauge value. The oil level in the bearing should be monitored regularly to ensure it is kept below that of 600C. If the color of the oil is so dark it should be replaced with fresh oil to maintain the proper function of the bearings.

Monoblock pump pre-conditioning

Various pre-initiation conditions must be checked before the operation of the pump.

  • The pump should first be primed using water and the output valve should be closed
  • The exact direction of revolution should be checked together with the starter wiring
  • All the operation guidelines should be followed to the letter

Characteristics features

  • It has a single shaft that guarantees the correct alignment over a long time
  • The pump features a running motor and a capacitor stator
  • The shaft is chrome coated to prevent rusting
  • It has a sturdy handle that makes it easier to lift
  • Rotary components such as impeller and rotor are dynamically balanced
  • Excellent suction lifting capabilities
  • capable of handling voltage instability

Common applications of monoblock pumps

  • Cooling water circulation systems
  • Domestic industrial water supplies
  • irrigation and cattle farming
  • Dewatering of coalfields
  • Dripping and lifting applications

Advantages of Centrifugal Monoblock Pump

  • simple in construction easy to operate
  • compact design hence takes less flow space
  • low initial installation cost and maintenance cost
  • Silent in operation with only little vibration
  • can deliver a large volume of water compared to its size
  • high power efficiency
  • Its construction allows design allows dismantling without removing the pump from the piping system
  • low running cost

Disadvantages of a Centrifugal Monoblock Pump

  • Initial manual Priming is a requirement either with some liquid or water
  • The operation may be noisy
  • Not suitable for very high heads
  • Limited suction lift. Can only raise water to 8 meters
  • Maximum efficiency is achieved over a short period
  • It is inefficient in handling highly viscous fluid

Selection of Centrifugal Monoblock Pump

Selection of the right monoblock pump for a particular application is a crucial stage in achieving the maximum pump performance in that application. The following are some of the useful parameters to consider during the selection of a monoblock pump.

Pump head

The pump head is the height to which the pump can raise water. The right pump model for household application should match the height (measured in ft or meters) to which you want to transfer the water.

Structure material

This factor does not influence the performance in a particular application but it contributes toward the service life of the pump. If a long service life is desired, monoblock pumps with a CI motor hosing and brass impeller offer the best choice.

Exit rate

The exit rate defines the volume of water pumped per minute. If the delivery area is quite large, a pump with a large exit rate capacity will be required. Therefore, the delivery area where the water needs to be delivered must be assessed before deciding on which pump to use.

Inlet and outlet size

The diameter of the inlet and outlet pipes must match the size of the supply pipe and the pipe connected to the storage tank.


The cost of the pump is yet another factor to consider during the selection of a pump for a particular purpose. In most cases, you would go for the option that saves you cost yet offers the most efficient performance. The most important thing is to compare the prices of different centrifugal monoblock pumps as well as their performance metrics to be able to decide on the most suitable pump for your application.

Monoblock pump maintenance

Mechanical inspections: The pump should be inspected to ensure mechanical mounting points are secure, mechanical seals and packing are intact to prevent leakage, ensure pump flanges and coupling are tight, and also the filters are clean and unclogged, replace damaged seals and hoses.

Lubrication: The motor and pump bearing should be lubricated according to the manufacture’s guidelines. However, care should be taken to avoid over-lubrication because it may lead to bearing damage. To get rid of excess grease, remove the vent cap and run the pump for about 30 minutes before restoring the cap. For the lubrication of elastomer seals avoid the use of oil, petroleum jelly, or silicone-based lubricants. According to most pump manufactures, such lubricants can lead to seal failure as a result of swelling of the elastomer. In addition, these lubricants are not capable of reactivating in the presence of water and may not be able to dry out rubber parts.

Electrical inspection: Ensure there are no loose connections at the wiring terminals, check that the motor vents and winding are free of dust/dirt, inspect the motor stator for overheating and arching, use a megohmmeter to inspect insulation failure.

Basic troubleshooting Centrifugal Monoblock Pump

The pump does not run

  • No electricity supplies
  • Defective motor winding
  • Loose connections
  • Blown fuse

Less discharge from the pump

  • wrong direction of rotation (change the polarity)
  • Available voltage is less (ensure the right voltage supply)
  • leakage in pipe
  • The impeller is excessively worn-out due to prolonged operation or high sand content in pumped water
  • The riser pipe is partly chocked by impurities (clean impurities)
  • The impeller is lodged with impurities
  • The discharge valve is partly closed (fully open the discharge valve)
  • The discharge pipe is coated with depositions

Total head developed is too low

  • Excessive wear of pump parts particularly the impeller (replace parts)
  • The discharge pipe is coated with impurities (clean the impurities)
  • leakage in the mechanical seals (replace seals)
  • The discharge line is closed and priming air can’t find the way out (open the discharge line)
  • leakage in foot valve or check valve (replace the valves)


This article has discussed in detail the concept of the monoblock pump, its components, working principle, application, advantages, and disadvantages. A monoblock pump means a mechanical instrument for moving fluid that consists of an impeller that strongly couples with an electric motor and revolving parts that are mounted on a single shaft. Coupled with desirable characteristics such as strength, consistent discharge, dynamically balanced rotor, and chromes coated shaft, Centrifugal Monoblock Pumps are the most considered choice of pump for agricultural, civil, and industrial uses. Some of the applications of the pump include irrigation, dewatering of coals fields, domestic and industrial water supply. The benefits of the centrifugal monoblock pump are many ranging from low installation and running cost to high-performance efficiency. However, it also has a few disadvantages such as the need for manual priming, limited suction lift, and lack of efficiency in dealing with viscous fluids. Generally, pumps are associated with many losses, but the losses are minimized in a centrifugal monoblock pump through the use of a steel casing that protects the motor. The selection of a centrifugal pump is based on various performance parameters (e.g., pump head and exit rate), construction material, and cost. For prolonged and efficient performance, a centrifugal monoblock pump requires maintenance of various electrical and mechanical components and this article also discusses some bits of maintenance tips.