Industrial Pumps Blog

Centrifugal pumps utilize a rotating impeller which serves to increase the pressure and flow rate of the fluid.  Centrifugal pumps are most commonly used to transfer liquids around piping systems.

Centrifugal pumps operate by the pressure differential created by the impeller.  The impeller’s rotation within the pump casing takes energy provided by the motor and accelerates the fluid away from the center of rotation.  This outward movement creates pressure due to being confined within the pump casing, and this in turn causes liquid flow.

The fluid being transported enters the pump along the axis of the mechanism, and may pass through a diffusing chamber after passing through the impeller mechanism.  The diffusing chamber may also be referred to as a volute chamber, and from here the fluid will enter the discharge outlet.  It is usual to find a centrifugal pump being used to high pressure discharge of fluids through small discharge heads.

A variant on the centrifugal pump is the screw centrifugal pump. This was developed in the 1960’s to handle delicate items which need to be transferred in bulk but at the same time must be handled without damage.  The first application was for transferring fish catches from trawlers nets into the holds of the boats, and again from the trawlers to dockside for processing.

The screw centrifugal pump is now commonly used to transport foodstuffs, crystal products, oily water and sewage.  The screw centrifugal pump is also capable of handling extremely long fibrous materials such as rope without jamming the pumping mechanism.  This makes this version of the centrifugal pump a favorite amongst municipal authorities who need sewage and waste removed and processed. The screw centrifugal pump also provides excellent flow control within its operating range, and again this makes it an excellent choice for handling delicate items.

Positive displacement pumps come in two main flavors: rotary and reciprocating.  Both have similar operating function; however there are distinct differences and applications for each type of industrial pump.

Rotary displacement pumps use rotation to create a vacuum which creates suction to draw fluid through the pump. The vacuum created displaces the fluid through the pump into the discharge pipe, hence the name positive displacement.  Rotary pumps are extremely efficient in operation as air is removed from the pump lines by the rotary action and this removes any need for air bleeding from the lines which is a manual operation.

There are some drawbacks to rotary pumps.  The differential between the moving, rotating parts and the pump enclosure are extremely close, which means the pump speed is limited to avoid erosion and excessive wear. High speed operation of rotary pumps generally leads to enlargement of the differential and a loss in pumping efficiency.

There are three main types of positive displacement rotary pumps.  The simplest are gear pumps which use two gear mechanisms aligned in parallel with enmeshed teeth.  The turning of the gears creates a flow of fluid between the teeth and outer body of the casing, with the fluid being discharged. Gears with a large number of small teeth generate a regular flow while larger and fewer gear teeth generate a pulsing flow which tends to flow in gushes.

Screw pumps are more complex and are comprised of two screws with counter threads which turn in opposition to one another. The screws are placed upon shafts with gears on them which are enmeshed with each other to generate a uniform turning movement of the two threads. The turning motion generates a fluid flow through the pump, but again the differential spacing between the pump casing and rotating threads must be minimalized to ensure efficient operation.

Finally, moving vane pumps comprise of a rotor mounted inside a cylindrical casing.  The turning rotor causes fluid flow between the pump housing and rotor which creates fluid flow through the pump.