End Suction Back Pull-Out Centrifugal Pump

End Suction Back Pull-Out Centrifugal Pump


What is an end suction back pull-out centrifugal pump?

An end suction back pull-out centrifugal pump is a type of pump that draws water axially into the suction and discharges it at 90 degrees to the suction; and is designed with a back pull-out design to facilitate rapid dismantling and re-assembly. The rotor assembly, including the impeller, pump shaft, and bearings, is attached to the power end, which can be pulled out of the pump casing after decoupling the motor and disconnecting the flange. Thus, the internal components can be serviced without disturbing the casing and associated suction and discharge piping. The end suction back pull-out centrifugal pump is often used for process pumps in the chemical industry because its construction facilitates easier field repair. The end suction back pull-out centrifugal pump manufacturers develop the edge cutting units to provide excellent performance parameters such as a maximum pressure head of 150 meters, pump capacity of up to 2200 cubic meters per hour, and motor speed of 3500 revolutions per minute (RPM).

End suction back pull-out centrifugal pump

Figure: End suction back pull-out centrifugal pump

Components of end suction back pull-out centrifugal pump

Electric motor

The motor is the source of the mechanical power to run the pump. The type of electric motor can be a single-phase or a three-phase induction motor.

Pump casing

The pump casing houses the impeller and the intake and discharge ports. It also contains the volute chamber, which helps with the conversion of the kinetic energy into the pressure head.

Impeller

The impeller moves the pumped liquid through the pump when it rotates. It is designed with blades that help to impart kinetic energy and to increase the velocity of the pumped fluid

Shaft

The pump shaft transfers mechanical torque from the motor to the impeller during pump operation. It is usually made from stainless steel and connects to the driver shaft via a coupling

Bearings

The ball-type bearings carry the shaft and the impeller, ensuring the correct alignment with the fixed ends under the axial and radial forces.

Coupling

The coupling connects the pump shaft and the motor shaft. Couplings have different types, including flexible coupling, rigid coupling, and close coupling. The pump head is directly mounted to the motor shaft in a close-coupled. Rigid and flexible couplings have separate pump and motor shafts that must be aligned, but the latter can accommodate minor shaft misalignment.

Suction inlet and discharge outlet

The suction inlet is the intake manifold, allowing the pumping fluid to enter the casing. The liquid exits the pump through the discharge outlet.


How does an end suction back pull-out centrifugal pump work

When the motor starts, the pump shaft rotates the impeller at very high revolutions per minute (RPM). As the impeller rotates, it displaces the priming liquid inside the pump casing, creating a vacuum in the impeller’s eye. Due to the atmospheric pressure outside the pump, more pumped fluid is forced into the pump through the suction inlet and toward the impeller’s eye to fill the void. So long as the impeller rotates, the liquid will be continuously drawn into the pump casing to be pumped. As soon as the pumped liquid enters the impeller, the centrifugal force acting on the impeller blades pushes the pumped liquid from the center of the impeller to the outer edges and into the volute casing at a very high kinetic energy and fluid velocity. In the volute casing, the speed of the fluid slowly decreases due to the gradually expanding flow path, and some of the kinetic energy is converted into static pressure energy. Finally, the liquid enters the discharge pipe perpendicularly to the suction line and at very high pressure, allowing it to be transported to the required destination.

Working of an end suction back pull-out centrifugal pump work.

Figure: Working of an end suction back pull-out centrifugal pump work.

Types of end suction back pull-out centrifugal pump

End suction back pull-out centrifugal pump with a long coupling

This end suction back pull-out centrifugal pump employs a long coupling between the motor and the pump head. Essentially, it has a separate coupling and motor. The long coupling design facilitates maintenance without disturbing the alignment with the electric motor.

End suction back pull-out centrifugal pump with a long coupling

Figure: End suction back pull-out centrifugal pump with a long coupling.

End suction back pull-out centrifugal pump with a close coupling

The End suction back pull-out centrifugal pump with along coupling is also called a monobloc, often in large end suction pump. In this pump, the motor is in the same unit as the pump. In other words, the rotor is directly mounted on the motor’s drive shaft. The pump’s operation is as simple as its construction.

End Suction Back Pull-Out Centrifugal Pump

Figure: End suction back pull-out centrifugal pump with a close coupling.

single stage end suction back pull-out centrifugal pump

The single-stage end suction back pull-out centrifugal pump relies on one impeller in the pump casing to perform the pumping action. This pump can be with a close coupling or long coupling. It is the most common end suction back pull-out centrifugal pump design and is relatively cheaper than the multistage counterpart.

Single-stage end suction back pull-out centrifugal pump

Figure: Single-stage end suction back pull-out centrifugal pump.

multistage end suction back pull-out centrifugal pump

The multistage end suction back pull-out centrifugal pump has more than two impellers mounted along the same pump shaft and housed in different chambers arranged in series. This pump can manage a higher-pressure head and fluid flow rate than its single-stage counterpart.

Applications of end suction back pull-out centrifugal pumps

The end suction back pull-out centrifugal pump manufacturers design the units to perform excellently as process pumps in oil refineries and the chemical and petrochemical industry. They also suit marine, environmental engineering, firefighting systems, etc. Typical uses of the pump include the following:

  • The end suction pull-out centrifugal pumps are used for hot and cold-water circulation. Also used for cooling water circulation.
  • They are used for virtually all transfer or circulation of liquid, for example, in handling clean or dirty liquids and liquids with low viscosity.
  • They are used for drip irrigation and water supply to residential and commercial buildings.
  • They are used to hand thermic fluids and volatile liquids.
  • They are also used for handling liquid containing significant solid particles.
  • They are used for handling chemicals and slurries.
  • They are used for condensate handling and refrigeration, and cooling tower installations.

Advantages of an end suction back pull-out centrifugal pump

  • End suction back pull-out centrifugal pumps have excellent operational efficiency.
  • They are back pull-out design facilitates easier maintenance of the pump’s internal components.
  • They have high reliability because the back pull-out design enhances failure avoidance and safety.
  • They have a compact design that is easy to install and operate.
  • They are highly versatile in applications.
  • They are suitable for hazardous fluids and clean and dirty liquids.
  • There is no chance of heat transfer hence no heat transfer problem.
  • They provide a wide range of flow rates to suit different application demands.
  • They have steady and consistent output.
  • They can withstand high system pressure and temperatures.

Disadvantages of an end suction back pull-out centrifugal pump

  • End suction back pull-out centrifugal pumps have a high initial acquisition cost.
  • They are prone to rust, which may potentially cause damage.
  • They are subject to cavitation, which may damage the impeller surfaces and the pump casing. Cavitation is the rapid formation and bursting of vapor bubbles within the pump. It occurs when the speed of the water causes it to vaporize, causing vapor bubbles in the liquid. The vapor bubbles suddenly burst near the impeller or pump casing surfaces leading to microcracking and corrosion.

Troubleshooting end suction back pull-out centrifugal pump

The motor fails to start

  • The power cable is broken. Consult a licensed electrical technician to inspect and replace any broken wires.
  • There is no power supply to control the Panel, or the power supply is inadequate. Check the main input panel. Ensure the power cable connections follows the end suction back pull-out centrifugal pump manufacturer’s guidelines.
  • The fuse is blown-out, or the circuit breaker is tripping. Inspect the pump for a blown-out fuse and replace it if necessary. Be sure to reset the circuit breaker if necessary.

The motor overheats and shuts off

  • Mismatch of the motor voltage and the line supply voltage. Check the motor supply voltage against the specification on the nameplate and adjust accordingly.
  • The impeller collides with the pump casing. Dismantle the pump, align the impeller or replace it.
  • Use of wire of wrong sizes. Make sure the wires in use satisfy the national electrical codes and the standards for circuit protection devices.

The pump gives zero flow after the startup

  • The suction lift is too high. Lower the pump or raise the liquid level in the tank
  • The pump is operating in reverse. Interchange the motor polarities. Check that the motor rotation direction matches the direction shown in the end suction back pull-out centrifugal pump manufacturer’s manual or the movement indicated using an arrow on the pump casing.
  • The manometric head is insufficient. Ensure all valves are open and the pipe diameter of the pipes meets the sizes set by the end suction back pull-out centrifugal pump manufacturers.
  • The impeller or check valve is clogged. Inspect the impeller and check valves, and clear any blockage.

The pump’s flow rate is unstable

  • The pump lifts liquid with air. Check the depth of the suction pipework or valve in liquid and deepen if required.
  • The bottom valve is leaking. Inspect the bottom valve for leakage and correct it.
  • The voltage is too low, leading to a decrease in pump speed. Check the power supply voltage and adjust it as necessary.
  • The pump lifts liquid with air. Check the depth of the suction pipework or valve in liquid and deepen if required.

The pump is vibrating excessively

  • The impeller is severely worn out. Inspect and replace the impeller with another from the end suction back pull-out centrifugal pump manufacturers. Ensure all valves are open and pipe diameters are correct.
  • There are unbalanced components in the pump. Inspect and rebalance the vertical inline centrifugal pump components as necessary.
  • The pump shaft is oblique or unbalanced. Inspect the post, rebalance it as required, or replace it.

The noise level is too high

  • Some parts are loosely tightened. Tighten the pump components to the torque level recommended by the end suction back pull-out centrifugal pump manufacturers.
  • Some pump components are excessively worn-out. Inspect the rotor assembly for worn-out bearings or impellers and replace them if necessary.
  • The pump is working outside the duty range. Ensure the pump works within the duty range specified by the end suction back pull-out centrifugal pump manufacturer.
  • The pump is working in cavitation. Ensure that the net suction pressure head meets the end suction back pull-out centrifugal pump manufacturer’s specifications. Make sure you open the suction line valves fully.

Summary

An end suction back pull-out centrifugal pump is a type of pump with an axially suction inlet and a discharge outlet oriented at 90 degrees to the suction inlet. The end suction back pull-out centrifugal pump manufacturers develop the units with a back pull-out design to facilitate rapid dismantling and re-assembly. The rotor assembly, including the impeller, pump shaft, and bearings, is attached to the power end, which is lifted and removed for maintenance whenever needed. Thus, the pump operator can service the internal components without removing the casing and its associated suction inlet and discharge outlet from the piping. The end suction back pull-out centrifugal pump is often used for process pumps because its construction facilitates easier field repair. They are evident in oil refineries, the chemical and petrochemical industry, marine, firefighting systems, etc. End suction back pull-out centrifugal pumps offer many benefits, including simplicity, easier maintenance, excellent efficiency, and reliability. They can withstand high system pressure and temperatures.