CENTRIFUGAL PUMP COMPONENTS

The following are the major components of a centrifugal pump and are shown in following figure.

                    

                     

Pump volute casing

Casing that receives the fluid being pumped by the impeller. The shape of the volute casing is in such a way that the cross sectional area gradually increases towards discharge resulting in the conversion of kinetic energy to the pressure energy at the discharge.

Impeller

Impeller is the main part of a centrifugal pump that pumps the process fluid from suction side to discharge side. It consists of equally spaced vanes around the impeller eye. Impeller eye is the entry point at which fluid enters into the impeller.

Shaft

The main function of the shaft is to transmit the torque and supports the impeller and all other parts of a centrifugal pump.

Key

Key is a metallic part which serves as a locking mechanism between the two rotating parts like impeller and shaft etc. It is installed in a groove called key way.

Shaft sleeve

Shaft sleeve is used to protect the shaft from mechanical damage caused by the seals or bearings and chemical damage caused by the aggressive fluids.

Bearings

Bearings give support to the shaft in rotation and also reduce frictional forces. In centrifugal pump bearings are usually designated as inboard bearing and outboard bearing.

Normally both radial bearings and thrust bearings are used in a pump to compensate for both radial and thrust loads.

Mechanical seal or gland packing

Mechanical seal or gland packing prevents leakage of the process fluid into atmosphere at a point where the pump shaft passes out through the casing.

Considerable minimum leakage is allowed in gland packing.

Approximately zero leakage is allowed in mechanical seal.

Gland packing is used in non hazardous services and mechanical seal is used for hazardous fluids where no fluid is allowed to leak into atmosphere.

Lantern ring

The lubricating or cooling fluid supplied to packing is distributed through lantern ring. It is commonly a brass ring with two holes that allows the lubricating or cooling fluid to easily pass through.

Bearing isolator

The bearing isolator solves the purpose of the following.

ü  To avoid the passage of process fluid to bearing housing.

ü  To avoid oil leakage from oil sump to outside of bearing housing.

ü  To avoid dirt into housing in dirty areas.

Deflector

If mechanical seal leaks then the deflector deflects the process fluid perpendicular to the shaft to avoid mixing with bearings and oil. It is generally made up of rubber or plastic.

Oil ring

Oil ring or oil flinger is used to circulate the oil in the oil sump.

Wear rings

These are placed at impeller and casing as to avoid the damage of the impeller and casing. Impeller wear ring gets damaged before the impeller damage and casing wear ring gets damaged before casing damage. These are easily replaceable parts.

Breather

It is a special part which let out the vapours liberated in the oil sump. Allows the air to enter and exit the lube oil sump without particulate contamination.

Gaskets

Gaskets prevent the leakage of the process fluid from wet parts of the pump to atmosphere.

These are placed mainly at five positions.

1.       Between impeller and impeller nut.

2.       Between impeller and shaft sleeve.

3.       Between back plate and casing.

4.       At drain plug.

5.       Between mechanical seal gland and seal.

The following are the wet parts of the pump.

ü  Volute casing

ü  Impeller nut

ü  Impeller

ü  Wear rings (casing wear ring and impeller wear ring)

ü  Back plate

ü  Shaft sleeve

ü  Mechanical seal or gland packing

ü  Seal gland

Throat bush

It serves as the restriction for the fluid flow between impeller and the mechanical seal area.

Constant level oiler

It acts as a lube oil reservoir to the lube oil sump and used to maintain a required level of oil in the lube oil sump for lubrication.

Bearing Housing

Bearing housing support bearings and protect from contaminants for lubrication.