A pump is a mechanical device that transports media by transforming the energy supplied by a motor into hydraulic energy. The first criterion for choosing a pump is the type of use and application concerned in terms of how it will be used from an end user point of view. The technical characteristics of this must be taken into account because they will determine the choice of pump.
Then, in order to properly dimension the machine and calculate the operating point of the pump, it is necessary to know the parameters of the network such as: flow rate, suction head, discharge head, head losses, etc.
How to best choose the correct pump for your needs and requirements
In order to choose a pump that meets your needs, you must determine its characteristics according to its use. First of all, you must determine what material and matter will overall be transferred. This is in order to avoid corrosion phenomena and therefore premature wear of your pump. It is therefore essential to know the chemical composition of the matter to be pumped. You also need to know of its viscosity and the possible presence of solid components. A thorough knowledge of all the physical properties of the treated fluid will allow you to choose the ideal technology for your application and the construction materials compatible with the pumped matter. There are chemical compatibility tables to consult before choosing the casing of your pump.
Look too at other key aspects such as the following:
- The flow you require: generally measured in m3/h (cubic meters per hour) or GPM (gallons per minute), the flow necessarily influences the size and dimensions of your pump;
- The suction head (height between the inlet of the suction pipe and the pump): as a general rule, the suction head must not exceed 10 meters. Beyond this, it is necessary to consider using a submersible pump.
- The discharge head (height between the pump and the discharge pipe outlet).
- The length of the discharge circuit.
- Head losses linked to obstacles on the pumping circuit (valves, bends, etc.).
- Whether there is a discharge tank or not could change the head.
- The temperature thus depends on the choice of pump casing
What you need to look out for
These different values allow you to calculate the NPSHa (Net Positive Suction Head available) of the setup. This will allow you to choose a suitable pump and avoid any risk of cavitation. You will also have to control the efficiency; which must be optimal at 30% more or less than the desired nominal flow rate.
The kinds of materials and matter to be pumped
The materials and material matter that needs to be transported is very important when choosing a pump. This is as the characteristics of the pump depend on its viscosity (i.e. the fluid’s resistance to a uniform flow), its suction temperature and whether or not there are solid elements in it. You will need to determine if the materials to be transported is chemically neutral or corrosive. You need this in order to choose the pump designed to operate under these conditions.
The flow of the materials
As a general rule, the more viscous the materials to flow, the more difficult the flow through your pumping system, but be careful, the viscosity of flowing materials varies according to operating conditions. There are 4 main groups of fluids according to their viscosity level; in the first group there are fluids such as water, oil or alcohol that move in the same way regardless of speed or level of agitation. For these types of uses you will not have many constraints in choosing your pump.
In the second group there are certain food products such as butter or cream whose viscosity increases with agitation; therefore, in these cases, a standard centrifugal pump will not be suitable for the fluid flow. The third group includes media that has a threshold to be exceeded before flowing. Once this point is reached, the viscosity decreases with agitation. Adhesives, paints and greases are part of the fourth group that are very thick at rest, but their viscosity decreases if constant agitation is maintained.
As a rule of thumb
Generally, for low viscosity fluids (the first and second group) centrifugal pumps are the most suitable because the pumping action generates a high shear rate of the fluid, as the viscosity increases you will have to take into account the additional resistance that the fluid will exert on the shear rate. On the other hand positive-displacement pumps are the best choice for viscous fluids (the third and fourth group) because they operate at lower speeds and the shear energy transferred to the fluids is lower than that of centrifugal pumps.
When should you use a diaphragm pump?
You can consider using a diaphragm pump when you need to transport very viscous or very dense materials. Generally these pumps are double-diaphragm to allow the suction and then the discharge of the media to be conveyed. These pumps can run dry: they do not require lubrication and are self-priming. These pumps are mainly used in the chemical industry. They are extremely flexible so they are now used in many sectors such as the food industry, electronics and the mining industry.
Generally, high-capacity diaphragm pumps are pneumatically operated. You should therefore consider checking the capacity of your pneumatic network if the pump is to be used in an industrial building, or provide an air compressor nearby if you need to use the pump outdoors.
Very important and worth knowing
Variety of product is another parameter that requires careful consideration when looking for in suppliers. To say in simple words, having a wide range of products provide more choice for customers and make them more satisfied. In recent years, globalization of markets has led to an increase in the product variety that customers demand. This has also seen a consequent increase in the number of variants of any given product line. This is in terms of what a manufacturer must supply. A multi-product company is a must. This is also key from an after sales point of view too.
