Services such as cooling, lubrication, flow transmission for processing and delivering power in hydraulic systems, and many other applications are just some of the services that pumps are used widely in the industry, and the existence of these pumps has helped to overcome many industrial problems. Even pumps are widely used in many industrial, office, commercial buildings, municipal buildings or even residential complexes as a pumping system for daily operations.
The pumps provide about 27% of the electricity needed for production operations in the manufacturing sector. Also pumps are used as heating systems, air conditioners (HVACs), ventilation or for supplying water for heat transfer in the commercial sector.
Water transfer and treatment of water and sewage, or even land drainage in municipalities, have been assigned to pumps, and in residential and office complexes, pumps as water supplies, especially for the upper floors, are widely used. The variation in the use of pumps and the different needs of pumps in different parts has led to a diverse range of pumps present on the market today, where pumps can be from a horsepower or even Half a horsepower, up to several thousand horsepower, is also on the market.
In addition, pumps not only have different sizes, but also different types of pumps. By adding energy to a ﬂuid, the pumps are usually classified.
In this regard, the pumps can be classified in the following categories:
- Types of positive displacement pumps that directly squeeze pressure to the fluid.
- A variety of centrifuge pumps, or, in other words, rotodynamic pumps that are used to increase the speed of fluids and actually convert kinetic energy to pressure.
There are different subsets in these categories as well. The types of lobes, sliding vane, pistons and screws are a subset of positive displacement pumps. And blended or mixed-ﬂow, axial or propeller types and radials are also from the subsystem of centrifuge pumps.
Several factors have to be investigated to determine which pump is suitable for an application. However, many of these pumps often cover similar cases.
The pumps must have high reliability, because this is often criticized. Keep in mind that pump failure in cooling systems is so important that it can lead to excessive damage to equipment because of overheating the equipment.
Even the operation of the pump in the lubrication system, if not fitted, can damage the equipment. Reducing productivity in most power plants and petrochemical plants is due to pump failure, which is sometimes very tangible.
Many of the daily facilities require a pump for their operation, and the partial pump is an integral part of these operations. This requires having a proper maintenance and repair systemand also tends to promote the practice of sizing pumps conservatively to protect the optimal performance of the pumps and to ensure the needs of different systems in different conditions.
Many engineers often overlook the overhead of pumps in order to make sure that the pumps are suitable for the system's requirements and that they are sufficiently large enough. However, the larger the pump size, the more safety it becomes.
Unfortunately, the lack of attention to the proper size of the pump and the inappropriate pump selection can greatly increase the maintenance costs of the system. In addition, the large pumps itself cost and require more maintenance than pumps with smaller dimensions and volume, and they must be repaired and maintained within shorter periods of time.
The excessive energy generated by large pumps causes the components of the system to become loose, which leads to valve failure, plumbing stress and even excessive noise.
Pumping System Components
Pumps, prime movers, plumbing or piping, valves and end-use equipment such as heat exchangers, tanks, thermal equipment and hydraulic equipment are the main components of a typical pumping system. In Figure 1 you can see a typical pumping system with its components.
As we explained earlier, although the pumps are made in a variety of types and in a wide range of types and sizes, but in general, the pumps should be classified into two categories: positive displacement pumps and pumps Centrifugal. In fact, according to the way the pump add the energy into the liquid flow, this category of pumps is done.
The difference between these two types of pumps is in the operation and type of their pumping so that the positive displacement pumps pressurize ﬂuid with a collapsing volume action often make the compression volume equal to the displacement of the system with each stroke or rotation of shaft But the centrifuge pumps work with the help of a rotary propeller and add kinetic energy to the electric current.
In this case, when the flow decreases in the pump diffuser section, the kinematic energy of the flume becomes pressurized.
Both positive displacement pumps and centrifugal pumps can provide a wide range of different types of applications, but nonetheless, centrifugal pumps are more commonly used and more common because both They are simpler and less risky. In addition, these types of pumps have a longer life expectancy and less maintenance.
Compared to positive displacement pumps, centrifugal pumps typically have less damage because they suffer from less abrasion and less need for replacement. Centrifugal pumps, as well as other pumps, require periodic mechanical sealing and packing, but the cost of these pumps is much lower and the cycle time is longer.
Another advantage of the centrifugal pumps is that these pumps can be used in a wide range of conditions, and they have almost no limitations. In addition, if this type of pump is used in inappropriate positions, the potential risk of damage to the equipment is lower, although precautionary measures should be taken in any case.
Centrifugal pumps have a variable flow or pressure relationship. When the centrifugal pumps are used against the high pressure system, the flow rate will be lower than those used by the low pressure system.
This is while centrifugal pumps are described by a flow or pressure relationship with a performance curve in which the flow rate is considered as a function of the head or pressure. Understanding these relationships is very important for choosing a suitable pump or designing an efficient system.
Positive displacement pumps, unlike centrifugal pumps, have a constant displacement volume. This makes the flow rate of these pumps directly equal to their speed and is proportional. In fact, the pressure in these pumps is determined by the system's resistance to current flow. Of course, it should be noted that positive displacement pumps have many special advantages that can be used well for residential and certain applications.
The most commonly used applications of the Positive displacement pumps include:
• For pumping liquids with high viscosity
- For systems that require high pressure along with low pump performance.
- For systems where the pump should be self- priming
- In systems that do not require a high shear force flow
- For systems that require accurate measurement and proper flow control.
- In systems where the pump efficiency is of great importance
Positive displacement pumps in each user application that are used should be considered in that system's safeguards or protection, like relief valves. The reason is the high power of these pumps, which can potentially move a large amount of fluid at high pressure, and this can put a lot of pressure on the components of the system.
For example, consider a system where all of its downstream pump valves are closed; in this case, a condition known as a deadheading, and this situation exists as long as an emergency valve operates. , So a piping or fitting failure occurs or the pump turns off. Of course, in these situations, valves are considered as safety valves to reduce the potential of the risk and protect the system, but relying on these relief valves cannot alone be a factor in not seeing this risk.
In addition, the softening valves or relief valves reduce the pressure by use of venting system ﬂuid, which cannot be responsive to all types of systems and may be harmful and dangerous for systems that are not well designed.
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