Centrifugal Pump - Beginner Guide

Centrifugal pump is Heart of unit nowadays in any industry. Different types of Centrifugal pump are used for different service. as a mechanical filed person it is very crucial to know basic information related to a centrifugal pump.
Basic Function of the pump is to transfer liquid from one place to another place with increasing pressure energy of the liquid.

PUMP THEORY 

The rotating impeller transmits or disseminates a centrifugal force and kinetic energy in the form of velocity to the fluid. The pump casing volute converts the kinetic energy of liquid into pressure head.

this energy change occurs by two part of the pump 1. impeller 2. casing volute or diffuser.the impeller is rotating part which gives kinetic energy to the liquid. and volute which is a stationary part that converts kinetic energy into pressure energy.

CLASSIFICATION OF PUMP

        1. POSITIVE DISPLACEMENT PUMP

• Reciprocating pump
• Rotary pump with single or multiple rotors

         2. DYNAMIC PUMP

• Centrifugal pump - radial flow, axial flow, mixed flow
• Jet pump
• Vortex pump
• Magnetic driven pump etc.

MAIN PART OF CENTRIFUGAL PUMP

CASING:-

a casing is generally in two types 1. volute 2. circular. the impeller is rotated inside the casing.

the casing may be axial split or radial split.

VOLUTE:-

Volute is a curved portion with increasing in area to discharge line of the pump. this volute reduced the speed of liquid and increase the pressure of the liquid.
The circular casing has stationary diffuser vane surrounding to an impeller. this type of arrangement used to convert velocity energy into pressure energy. this arrangement used in a multistage pump.
there is two type of volute use in pump.1. single volute 2. double volute

Normally we have seen single volute in many pumps. double volute spacially use for balancing of pressure around impeller in a casing. double volute minimizes imparting a radial force on the shaft and bearing due to imbalacing pressure around the impeller.

IMPELLER

There is normally three type of impeller used in the centrifugal pump.

1. Open impeller 2. Closed impeller 3. Semi-open impeller

• Open impeller has blade mounting and there is no shroud.
• Semi-open impeller have a shroud on which blade positioned
• Closed impeller most popular and most usable impeller in which shroud cover from both side of the blade with impeller eye on another side to allow liquid to enter into the impeller.

PUMP SHAFT

A shaft is a most important part of a pump on which all other parts are mounted. a shaft is made from steel or other corrosion resistant material.

BEARING HOUSING

A bearing is fitted on bearing housing to control the axial and radial movement of the drive shaft. normally bearing housing has two sides namely Drive end which is situated at coupling side and other is Non Drive end which situated at casing side. on this, both end bearings are fitted. generally, radial bearing is fitted on drive end and Thrust bearing fitted on non-driving end.

WEAR RING

Wear ring fitted on impeller as well as in casing. The clearance between impeller and casing to prevent wear of impeller or casing but allow fluid to leak back from the discharge side to suction side of the pump.

MECHANICAL SEAL  OR GLAND PACKING

A mechanical seal is a heart of the pump. As on another side, soft material packing is used to prevent leakage.

mechanical seal use for high toxic, hazardous and highly flammable media.packing use for normally water pumps and non-toxic media.

PUMP POWER AND EFFICIENCY:-

The input power from motor P (in KW) is transferred to the driving shaft of the pump(converting mechanical power to rotate shaft)

So,

Hydraulic Power = ρ.g.Q.H

where,

ρ= density of a fluid in kg/m3

g= gravitational acceleration 9.81 m/s2

Q= pump capacity (discharge) in m3/sec

H= total pressure head in M

Efficiency =  hydraulic power of pump/input power or shaft power

TROUBLESHOOTING OF CENTRIFUGAL PUMP:-

PROBLEM - NO DISCHARGE IN PUMP  VIBRATION

• Vapour lock                                                      
• Remedies: Check suction line is properly submerged.         
• Air trap in suction  
• Remedies: Check for proper venting of the system
• Insufficient NPSH 
• Remedies: Check for proper levelling of the source of suction like a tank, column, vessel etc
• Wrong direction of rotation
• Pump jammed                                    
• Remedies: Check that impeller is not clogged

PROBLEM - VIBRATION

• misalignment         
• loose foundation bolt
• defective bearings
• impeller unbalancing              
• runout in shaft              
• vaporization in suction

TYPE OF CENTRIFUGAL PUMP

1. Single stage pump
2. Single stage Double suction pump
3. Multistage pump
4. Vertical pump
5. Sudyne pump
6. Magnetic driven pump
7. Submersible pump
8. Booster pump

                                                              END