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When choosing a slurry pump for your system, you must keep in mind the task of the pump and the characteristics of the application you are interested in.
In fact, one of the most classic mistakes you can make is to only take into consideration the purchase price that it will have, without understanding and foreseeing the problems that you may have during operation.
First of all, in pressure transfer or filter press feeding applications, centrifugal pumps are often used without a precise technical reason.
In fact, it is true that this type of pump may cost less in terms of the initial purchase, but it is equally true that dynamic pumps – centrifugal pumps are part of this type – have limitations and disadvantages that we will now see.
First of all, centrifugal pumps, for filter press or other applications, unless we go very high with sizes – and therefore with costs – rarely exceed 6-7 bar pressure.
So, if you have an application where you need to go beyond that, you will definitely be travelling on orders of installed power that can become significant – for the same performance with a volumetric.
Secondly, you must consider that centrifugal pumps have an efficiency that is not constant and is only maximum at one point.
In fact, if we analyse the characteristic curve of a centrifugal pump, we see that optimum efficiency only occurs at a certain point representing a pair of values Head (and therefore pressure) / Flow rate: there is only one point for which maximum hydraulic efficiency is obtained.
Outside this point, the efficiency always drops, so if you vary the flow rate or the pressure you have in your system or application, the efficiency of the pump – which depends on the speed triangles and therefore on how the pump is constructed – will drop inexorably.
Translated simply: if you find yourself operating your pump in a flow and pressure condition that is not optimal (so you will always have this condition), you have to put your hand in your wallet because low efficiency means higher energy consumption.
In essence, therefore, every time the operating condition in your system shifts away from the pressure and flow rate values that correspond to maximum efficiency, you are losing money because you have more wasted energy (the pump is not working well in that operating condition).
With positive displacement pumps, this can be avoided, as the efficiency is practically always constant and the flow rate does not vary with pressure.
This is an intrinsic feature of all positive displacement pumps, and therefore also of piston or piston-diaphragm pumps: the flow rate is constant irrespective of the pressure value generated (or even the other way around). This is because, the pressure is decided by the operating conditions on the operator side.
In this way, your output does not change as the process parameters vary, but always remains at optimum values.
The fundamental characteristics of volumetric machines are:
–Prevalence (and therefore pressure) supplied to the fluid independent of rotation speed with the possibility of reaching very high values
–Supplied flow rate independent of the head and directly proportional to the speed of rotation (which for reciprocating pumps is of modest values)
-Possibility of pumping thick liquids and various slurries
-Internal losses practically independent of head and correspondingly possibility of very high efficiency at high heads
If, on the other hand, you want to modulate the power absorption of your sludge pump according to the real needs of your plant, and in this way save even more (i.e., gain during use) then you can use a pump from the Autemi range, equipped with the ESS system.