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Small explanations about the pump
The term pump indicates a particular operating machine which, by using some moving mechanical parts, is able to lift, move from one area to another or even only to collect liquids and gases. The pumps are used indoors, often between two ducts, one of suction and the other of delivery. It is important to underline that several manuals designate only those machines capable of moving and collecting liquids, while using the term compressor to indicate all the appliances capable of moving, not liquid, but gaseous fluids. Each pump is distinguished, first of all, by the use and the liquid with which it is necessary to work, but above all by certain characteristics of use, such as the flow rate, the prevalence and the driving force that is able to apply to the situation. Photo taken from www.kar-el.com.tr
Short historical references
The pump instrument has much older origins than one might think: it was, in fact, Archimedes who conceived and described for the first time a machine similar to modern pumps; it was a rotating instrument able to move constant quantities of liquid with each rotation. To avoid that it could be shelled with each use, it was used only for minimum quantities. In the Middle Ages it was possible to improve the work of Archimedes and expand it to large quantities; from these studies was born the noria, which, at present, is still used in specific farming techniques. The progress of science over the years has led to the development of different pump operating systems such as those with rods and crank and those with cylinders and piston.With the introduction of steam it has also been possible to improve individual performance. Finally in the last century it has been possible to build pumps of dynamic type. Photo taken from italian.thermal-oil-boilers.com
The main characteristics of the pumps, besides the model and the type, concern the flow rate, the head and the pumping speed, as well as the type of liquid with which one works and the motive power that is able to apply to the job.
As far as the flow rate is concerned, this is indicated by the letter Q and indicates the capacity of movement of the fluid volume in a given period of time, and is usually expressed in m ^ 3 / s.
With reference to the pumping speed, instead, we refer to the volume of the displaced fluid, but this time as a function of time.
Ultimately we talk about the prevalence, indicated with the letter H, for what concerns the maximum lift height that the pumps are able to perform at the top of the possible performance, and is normally expressed with the unit of measurement of the meters .
Pump: The NPSH parameter
In addition to the various technical characteristics that differentiate the different types of pumps, particular attention must be paid to a parameter that could be secondary, but which is absolutely not: the NPSH.
This abbreviation is the abbreviation of Net Positive Suction Head and indicates the difference that can be between the pressure in a specific point of any hydraulic circuit and the vapor pressure of the liquid in the same point where there is pressure.
On the basis of this characteristic, however, there are several limitations in the suction phase regarding any type of pump, whatever the technology with which it works.
All this is because it is necessary to remember that suction is carried out exclusively by pressure difference thanks to a decompression in the suction area.