A pump is a mechanical device that transfers fluid by converting the energy provided by an electric motor into hydraulic energy. The first criterion for choosing a pump is undoubtedly the type of fluid. The technical characteristics of the fluid must be considered as they will determine the ideal type of pump.
Next, to correctly size the machine and calculate the operating point of the pump, it is necessary to know the network parameters such as flow, suction height, discharge height, head loss, etc. This guide provides an overview of the main types of pumps and the situations in which they are most commonly used.
However, this section does not cover hydraulic pumps (or power pumps) and vacuum pumps. Both products differ in application and technology and will be introduced and described separately.
How to choose a pump?
In order to select the most suitable pump, its characteristics must be determined according to its application. First of all, it is necessary to ask what type of fluid must be pumped in order to avoid the phenomenon of corrosion and therefore premature wear of the pump. Therefore, it is necessary to know the chemical composition, viscosity, and possible solid content of the fluid. In-depth knowledge of all the physical properties of the treated fluid will allow the selection of the ideal technology and building materials compatible with the fluid for each application. Before choosing a pump housing, there are some chemical compatibility tables to refer to.
Second, attention must be paid to the properties associated with fluid transport, in particular:
· Required Flow: Usually expressed in m 3 /h — cubic meters per hour —, l/s — liters per second — or GPM — gallons per minute —. Therefore, flow affects the size and dimensions of the pump.
· Suction stroke – the height between the suction pipe and the pump -: In general, the suction stroke should not exceed 10 metres. If not, it may be necessary to consider a submersible pump.
· Discharge Head: Height between the pump and discharge pipe outlet.
The length of the discharge loop.
Pressure loss due to obstructions in the pumping circuit (valves, elbows, etc.).
· Is there a drain tank that can change the pressure?
· The choice of pump casing depends on the temperature.
· These parameters are used to calculate the installed NPSHA (Net Positive Tips Available). All of these help in choosing the right pump to avoid any cavitation risk. The performance also needs to be monitored, which should be optimal at plus or minus 30% of the desired nominal flow.
Criteria for choosing a pump
· Load loss.
Why is it necessary to know the properties of the fluid to be pumped?
The type of fluid to be conveyed plays a very important role when choosing a chemical pump, as the characteristics of the pump will depend in particular on the viscosity (ie the resistance of the fluid to its movement), the suction temperature and the presence or absence of solid elements in the fluid. In order to choose the right pump to work under these conditions, it is also necessary to know whether the fluid being conveyed is chemically neutral or corrosive. Generally, the more viscous the fluid, the more difficult it is to flow through the pumping system. Also, the viscosity of the fluid varies depending on the operating conditions.
There are 4 main groups of liquids depending on the amount of viscosity: the first group consists of liquids such as water, oil or alcohol, all of which move the same, without any movement or high mobility. There are not many criteria for choosing a pump for these types of applications. The second group contains other foods, such as butter or cream, whose viscosity gradually increases. Therefore, in these cases, a standard centrifugal pump is not sufficient to circulate water. The third group includes water points. When this time is reached, the viscosity decreases and decreases. Finally, glue, paint or glue falls into the fourth layer. They are very thin in comfort, but if stored regularly the viscosity decreases.
When to use a centrifugal pump?
If you need to pump low viscosity liquids that may carry solid elements, consider using a centrifugal pump. Centrifugal pumps are sturdy devices with the good performance overall. This type of pump allows the pumping large volumes of liquid at a constant flow rate. They usually don’t suck on their own. Therefore, it must be possible to independently fill the circuit before the pump is put into service. This type of pump can also be thought of as feeding sewage treatment plants or conveying thick liquids or cleaning fluids, as is the case in the petrochemical industry.
When to use a peristaltic pump?
Peristaltic pumps suitable for clean, sterile or corrosive fluids can be envisaged when it is necessary to ensure that the fluid being pumped is not contaminated by foreign substances. These pumps can exactly meter liquids. In fact, with this type of pump, the liquid moves through pipes or conduits and therefore does not come into contact with the pump body, thus guaranteeing hygienic pumping.
They are self-priming pumps because the receipt of the tube creates a priming action and allows the pump to expel fluid containing air or possibly gaseous residues.On the other hand, these pumps are bulkier compared to other pumps of similar flow. Furthermore, since the peristaltic pump works by pulsation, the flow rate is not constant.
When to use a diaphragm pump?
Diaphragm pipes are an option when viscous and thick fluids need to be transported. As a general rule, these pipes are two diaphragm pipes, allowing water to flow in and out. These pumps can be extremely dry: they do not need lubricating oil and are self-adhesive. It is widely used in the chemical industry, but because it is highly flexible, it has already been used in many fields, including food, electronics, and mining.