CHEMICAL ADDA: TYPES OF PUMP

Pump

A pump is a device that moves fluids (liquids or gases), or sometimes slurries, by mechanical action.
The basic purpose of pump is to transfer fluid or liquid or gases or slurries from a lower level to higher level.
The pumps increase the mechanical energy of the liquid, increasing its velocity, pressure or elevation or all three
Pump are widely used in variety of application
Pump exist in a variety of shapes and sizes, depending on their intended function.
When the flowing fluid is a gas, the pump is typically referred to as a compressor.
There are two major classes of pump

Positive displacement pump

It is the first major class of pump.
In this pump, a definite volume of liquid is trapped in chamber, which is alternately filled from the inlet and emptied at a higher pressure through the discharge.
Positive displacement units apply pressure difference directly to the liquid by a reciprocating piston, or by rotating members which form chambers alternately filled by and emptied of the liquid.
Positive displacement pumps are a category of pumps designed to move fluid at a steady rate through a system.
These pumps are able to handle viscous fluids, which flow at lower speeds and create more resistance, more efficiently than kinetic (dynamic) pumps.
There are two sub classes of positive displacement pumps.

Reciprocating pumps

In reciprocating pumps, the chamber is a stationary cylinder that contain a piston or plunger or diaphragm.
They utilize a piston, plunger or diaphragm which draws fluid in (upstroke) and pushes it out (downstroke), using check valves to regulate and direct flow through the system.
In a reciprocating pump, a volume of liquid is drawn into the cylinder through the suction valve on the intake stroke and is discharged under positive pressure through the outlet valves on the discharge stroke.
The discharge from a reciprocating pump is pulsating and changes only when the speed of the pump is changed. This is because the intake is always a constant volume.
Often an air chamber is connected on the discharge side of the pump to provide a more even flow by evening out the pressure surges.
Reciprocating pumps are often used for sludge and slurry.
There are three example of reciprocating pumps

Piston pumps

In piston pump, liquid is drawn through an inlet check valve into the cylinder by the withdrawal of a piston and then is forced out through a discharge check valve on return stroke.
Most piston pumps are double acting with liquid admitted alternately on each side of the piston so that one part of the cylinder is being filled while the other is being emptied.
The piston may be motor driven through reducing gears , or a steam cylinder may be used to drive the piston rod directly
The maximum discharge pressure for commercial piston pumps is about 50 atm.

Plunger pumps

For high pressure plunger pumps are used
A heavy walled cylinder of small diameter contains a close fitting reciprocating plunger, which is merely an extension of the piston rod
At the time of stroke plunger fills nearly all space in the cylinder.
Plunger pumps are single acting and usually are motor driven
They can discharge against a pressure of 1500 atm or more.

Diagram pumps

In a diagram pump, the reciprocating member is a flexible diaphragm of metal, plastic or rubber
This eliminates need for packing or seals exposed to the liquid being pumped, a great advantage when handling toxic or corrosive liquid
Diagram pumps handle small to moderate amount amounts of liquid, up to 100gal/min, and can develop pressure in excess of 100 atm

Rotary pumps

A wide variety of rotary positive displacement pumps are available.
They bear such names as gear pumps, lobe pumps, screw pumps, cam pumps, and vane pumps.
Rotary pumps do not contain check valve.
Rotary pumps operated best on clean, moderately viscous fluid, such as light lubricating oil.
In rotary pumps discharge pressures up to 200 atm or more can be attained.

CHEMICAL ADDA