Pump and dredging dewatering specialist IPR asserts that it has the expertise to guide customers in selecting the most suitable dewatering pump for specific applications.

IPR rental development manager Steve du Toit notes that the concepts of head and pressure are important elements to consider when selecting a pump.

“The pump head is the height to which a pump can raise fluid – measured in metres or feet,” he explains. “The head is important when specifying centrifugal pumps because their pumping characteristics tend to be independent of the fluid’s specific gravity, which can also be referred to as relative density.”

He highlights that there is a close relationship between the two parameters, but that the most important distinction is that head is independent of the fluid characteristics.

“In other words, regardless of the fluid’s relative density, the pump will lift it to the same height,” he says. “It does not matter, therefore, whether the fluid is just water or a heavy sludge.”

Pressure, however, is dependent on the fluid being pumped, and is affected by gravity. As a result, the same head will generate a different pressure – depending on the fluid’s relative density.

“Suction conditions are also relevant to the pump head,” continues Du Toit. “So if the suction level is lower, the head measured will be less.”

He explains that the motor of the pump converts electrical energy into mechanical energy, which is then imparted into the fluid as pressure. When the suction level is raised or reduced, the potential pressure of the liquid is adjusted accordingly. The more pressure a pump can deliver, the higher the head will be.

“Of course, pump manufacturers cannot know your suction level parameters, so they calculate the pump’s total head,” he says. “This is done by subtracting the total suction head – measured as height above sea level – from the total discharge head.”

He notes that the amount of friction also needs to be considered, as there are substantial losses in the pumping circuit owing to friction, depending on the length and diameter of the pipe itself, as well as the bends and gate valves through which the fluid flows.

“The sum of the head and friction loss will result in the total head, which is a more reliable indicator of pump performance than pressure,” says Du Toit. “The total head indicates what the pump can do regardless of the suction conditions; when combined with your flow requirement, the total head will allow you to choose the right pump.”

He continues to explain that the performance of a pump at a certain speed, or revolutions per minute, can be found in the manufacturer’s datasheet, displayed as the flow rate (or Q) versus head curve. The flow will have zero or little flow at its maximum head, which is also sometimes called the shut-off head. Pump users need to ensure that the pump they choose has enough flow at the head they require.

“Remember that this selection procedure only applies to centrifugal pumps,” he adds. “Piston pumps can provide more pressure, and they are selected based on flow only.”

A final note on selecting the correct pump is to ensure that the units being referred to by original equipment manufacturers and service providers align with the units being used – whether imperial (such as gallons/minute), or metric ­(litres/minute, cubic metres/hour and litres/second).

IPR was recently appointed by Atlas Copco as a master distributor for the Southern African region and highlights its extensive range of dewatering pumps.