Page 59 - Commercial Catalogue 2011

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Water Pumps
There are many different types of pumps available on the market today, each designed to fulfil a
specific function.These pumps can be divided into the following two broad categories:-
1. Positive Displacement Pumps
Create increasing pressure
Examples: peristaltic, single diaphragm, double diaphragm, piston, progressive cavity
2. Centrifugal Pumps
Create a specified head
Examples: end suction, submersible, split horizontal, vertical long shaft pump
The most common pumps utilised in the aquatics and aquaculture industries, and those supplied by
TMC, belong to the second category.
All of the pumps in this catalogue have been carefully selected for their suitability for both fresh and
saltwater applications, along with tried and tested reliability and a long service life. Our range of
plastic-bodied pumps has been extended to include units up to 7hp and flows up to 60m
How Does a Centrifugal PumpWork?
As the motor driven impeller rotates, mechanical work is transferred to the water which is moved by
the centrifugal force generated. The energy transferred is in the form of higher speed and higher
pressure.As the water enters the impeller it is centrifuged out along the blades and then forced out
into the pump housing.The job of the motor is now done as the water has the necessary energy.
The energy transferred to the water is in two forms:-
• A static rise in pressure caused by centrifugal force.
• A dynamic rise in pressure caused by increased speed.
As we do not want a greater volume of water to leave
the pump than is entering it, we want to convert the
excess dynamic pressure into static pressure by reducing
its speed (no energy is lost – it can only be converted to
other forms).This can be achieved by the use of a spiral diffuser (a funnel like tube) and decentrally
located impeller.This provides more and more room for the water flow to move away from the
impeller.As the flow is constant through the pump it results in a reduction of speed and therefore an
increase in static pressure and thus a head of fluid can be generated.
Guidelines for Selecting the Correct Pump
In order to ensure the correct flow rates for any application, it is essential that the correct pump is
selected. Failing to spend some time selecting the correct pump can result in filtration components not
operating correctly, desired flow rates not being achieved, or pumps operating outside of their designed
range.The following simple steps will help you to select the correct pump:-
1. Determine the required flow rate. This will entail calculating the volume of the tank, and deciding on
how many times an hour this needs to be turned over. For example, if you have a 1000 litre tank, and
it requires a 4 times an hour turnover, then the required flow rate will be 4000 litres per hour (or