Pumps and Its Types | Fluid Dynamics

What is a Pump?

A pump is a mechanical device which uses some energy in the form of electricity and transport fluids such as liquids, gases, and slurry from one place to another place.

Types of Pump:

There are two main types of Pumps:

1. Positive Displacement Pumps (PD Pumps)

2. Centrifugal Pumps

Mostly Pumps are used for Commercial purposes as well as Domestic purposes. Best Example of the use of Pump for Domestic purposes is the pump we use in our houses with the help of which we transport underground water to the tanks for use it later.
Most pumps are used to transport volume of a fluid from lower height to a higher height as described in the above example.

Positive Displacement Pumps:

PD Pump is usually used to feed chemicals into water and to transport heavy fluids like sludge.

The power of a Large Piston Pump is usually connected with an Electric motor connected to the Piston with the help of gearhead and connecting rod. PD Pumps are further classified into following types:

1. Reciprocating Pumps:

Piston Pumps, Plunger Pumps, and Diaphragm Pumps are included are the included in the class of Reciprocating Pumps. In Piston, pump fluid is withdrawn into cylinder passing through the check valve and pumped out by discharge section by outlet check valve. Most Piston pumps are double acting in which fluid is sucked from one side and at the same time is pumped out from the other side. Often one or two cylinders are used in parallel with common suction and discharge headers and configurations are made in such a way that to minimize the fluctuation in the discharge section. The piston may be motor driven through reducing gears or a steam cylinder may be used to drive piston rod directly. The maximum discharge pressure for the commercial piston pumps is 50atm.

For the high-pressure discharge of fluid plunger pump is used. In plunger pumps, a heavy walled cylinder with small diameter contains a close-fitting reciprocating plunger which is merely an extension of the plunger rod. While working, plunger fills all the empty space in the cylinder. Plunger pumps are usually motor driven and single acting. They can discharge fluid at a pressure of 1500atm or more.

In a Diaphragm Pump, the reciprocating member is a flexible diaphragm of Plastic, Rubber, and metal. Diaphragm pumps are very effective when dealing with toxic or corrosive liquids. Diaphragm pumps can handle from small amount of liquids to a large number of liquids up to 100gal/min and can create a pressure up to 100atm.

The mechanical efficiency of Reciprocating pumps range from 50% to 70% from small pumps and 70% to 90% for large ones. Mechanical Efficiency of Reciprocating pumps is nearly independent of speed within normal operating limits and decrease slightly with the increase in discharge pressure due to increase in friction and leakage.

2. Rotary Pumps:

A wide variety of Rotary Positive Displacement Pumps are also available with the name of Gear pumps, Lobe pumps, Vane pumps, Screw pumps, Cam pumps. Unlike Reciprocating pumps, Rotary pumps have no check valves. Closeness between the rotating and stationary parts of the rotary pumps decreases the chances of leakage and prevent liquid to move from discharge space to back suction space. They also limit the operating speed. Rotary pumps operate best clean, moderately viscous fluids such as light lubricant oils. Discharge pressure of 200atm or more can be attained. Gear pumps are further classified into two more classes:

1. Spur Gear Pump:

In Spur Gear pump, intemeshing gears rotate with close clearance inside the casing. Liquid entering the suction line at the bottom of the casing is caught in the spaces between the teeth and the casing and is carried out to the top of the casing and forced out to the discharge.

2. Internal Gear Pump:

In internal Gear Pump, pinion meshes with the ring gear with internal teeth. Both gears are inside the casing but the pinion which is externally driven is mounted eccentrically with respect to the center of the casing. A stationary metal crescent fills the space between two gears.  Fluid is carried from inlet to outlet by both gears, in spaces between the gear teeth and crescent.

Centrifugal Pumps:

Centrifugal Pumps uses Rotational Kinetic Energy of the pump and increase the velocity of the fluid and then converts that velocity into the flow. Fluid is forced into the impeller either by atmospheric pressure or by some sort of jet that is artificial pressure.

Working of Centrifugal Pumps:

In Centrifugal pumps, the liquid enters through the suction connection concentric with the axis of a high-speed rotary element called "Impeller" which carries radial vanes integrally cast in it. Liquid flows outward in the spaces between the vanes and leaves the impeller at a considerably greater velocity with respect to the entered liquid velocity. In a properly functioning pump, space is completely filled with the liquid without cavitation. The liquid leaving the outer periphery of the impeller is carried out in a spiral casing called "Volute" and leaves the pump through a tangential discharge connection. In the volute, the velocity head of the liquid is converted into pressure head of the liquid. The power is applied to the fluid by the impeller and power to volute is delivered by rotating shaft to which volute is connected. The rotating shaft is usually connected with a motor which rotates the shaft at a speed of almost 1750 rev/min.

Under Ideal conditions of frictionless flow, the mechanical efficiency of is definitely 100%.

Centrifugal pumps are most common pumping machine that is practiced in most ordinary plant practice. They are available in a number of types after simple volute machines

Uses of Pumps:

Pumps have two main purposes:

1. Circulate fluid within the system.

2. Transfer of fluid from one place to another.