What is a pump? People’s access to water has been one of the most important concerns of humans since the first days of collective life, and in order to access different water sources, it was necessary to move and transfer water to provide the water needed by the people and have relatively easy access to water, these needs It led to the invention of the first pumps.
What is a pump?
In simple words, pumps are a device for lifting, moving and transferring or compressing fluids (liquids and gases). The operation of the pump is based on the principle of system operation called “absorption and discharge”. Pumps use mechanical power to collect fluid from an input point (usually a reservoir or source) and move it to an output point (such as a pipeline or a distribution system). This fluid transfer operation can be done vertically or horizontally and is used in many industries and sectors. Pumps use different sources to receive mechanical energy, such as hand power, electricity, wind, motor, etc.
The first pumps
As it was said in the introduction of the article, the feeling of the need of humans to transfer water led to the construction of the first pumps. Mining, raising water, and transporting river water to different areas of the cities were among the activities that awakened the need for pumps in the city. The first pumps were devices for raising water, such as Persian and Roman water mills, Archimedes screw was also one of the more advanced examples of early pumps.
In the Middle Ages, mining also led to the development of piston pumps, many of which were described by Georgios Agricola in De re metallica. The piston pump works with air pressure. When the piston rises, it creates a slight vacuum; Since the pump has an outlet, the outside air pressure forces the water into the cylinder. Atmospheric pressure alone can throw water up to a maximum height of 10 meters, so a force piston pump is made to drain deeper mines. In these pumps, the downward movement of the piston expels water through a side valve to a height that depends solely on the force applied to the piston.
What is the use of the pump?
Pumps are used to transfer fluid to a certain height or move it in a piping or hydraulic system to perform work such as hydraulic lifts. In more general terms, a pump is a device that moves incompressible fluids from one point to another. The use of pumps is not limited to moving and transporting water and they have many applications in various industries. Probably, the most common use of the pump that you have come across is its use in buildings to provide proper water pressure in the upper floors, but pumps in urban construction for the purpose of transferring water, in the urban sewage system and inside sewage ponds and wells, in The agricultural industry has many applications in order to irrigate lands, in the oil and gas, food, pharmaceutical and other industries. Also, in buildings, pumps are used to provide hot and cold water, air conditioning systems, swimming pools and fire fighting systems.
Common terms in pumps
To fully understand pumps, you must be familiar with the common terms that you will encounter in units of measurement, components and other parts related to pumps.
What is the flow rate of the pump?
The amount of fluid passing through a section per unit of time is a definition of flow rate and it is usually represented by Q. According to different needs and cases, there are different types of pumps, including linear pumps, rotary pumps, centrifugal pumps and submersible pumps. Each type of pump is designed and used for specific applications. Flow measurement is mainly based on two categories of measurement units:
- Mass units: The mass flow rate of the fluid is calculated in a certain fraction of time, such as Kg/h.
- Volumetric units: the volume flow rate of the fluid is calculated per unit of time, such as lit/min (liters per minute) and m 3 /s (cubic meters per second).
In other words, the amount of fluid or liquid that passes and exits in a specific unit of time from a specific point such as the pump outlet or the cross-sectional area of the pipe is called flow, which can be expressed in liters per minute, liters per second and or cubic meters per hour.
It should be noted that there is a similar proportion between the amount of fluid passing through the pipe and the amount of electricity passing through a wire, so that the amount of hydraulic head is equal to the amount of voltage and electric potential energy, and the amount of hydraulic current is equal to the amount of amperes and electric current. .
As the thinner the electric current transmission wire, the amount of current passing through the wire decreases, as the diameter and cross-section of the water transmission pipe decreases, the flow rate also decreases. Just as we need a voltage difference to transfer electricity to the electric cable through the wire, a special head must be defined to transfer the fluid in the pipe.
Determining the same head value on both sides of a horizontal pipe causes the fluid inside the pipe to have no flow because, just like an electric cable, it resists the passage of electricity.
What is the head (height) of the pump?
It means how high a pump (in standard conditions) can raise the fluid under pressure. For centrifugal water pumps, head or water pressure is expressed in meters (m) or feet (ft), and for rotary and positive displacement pumps, pump pressure is expressed in bar, PSI, and kilopascals (kpa). .
In other words, Head means height and refers to the difference in level. For example, a pump with a flow rate of Q per second and a height of 30 meters can pump Q liters of fluid per second to a height of 30 meters. The amount of pumping height of each pump is calculated based on the diameter of the impeller and the rotation speed of the pump motor, and the type of pumped fluid is not important.
In other words, in the above example, the pump is able to pump Q liters of pumped fluid, whether clear water, oil or mercury, etc., to a height of 30 liters per second, and the difference is only in the amount of power consumed by the pump to pump different fluids. be
What is pump pressure?
The amount of pressure means the amount of pressure exerted on each unit of the earth’s surface (for example, Kg/cm 2 ) and care should be taken not to be confused with the height value. In the case of pumping liquids, the amount of pressure that the liquid exerts on the surface of the earth is equal to the product of the pumping height and the specific weight of the pumped liquid.
Therefore, the volume of several kilometers of air on the surface of the earth, on the surface of the sea only a pressure equal to one Kg/cm 2 produces a pressure close to almost one atmosphere. But the same volume of pressurized liquid produces 700 to 800 times the air pressure. Because the specific weight of liquid is 700 to 800 times greater than the weight of air.
Keep in mind that the pressure of water at a height of 10 meters is something close to one Kg/cm 2 is. By installing a manometer at the pump outlet, the following pressure increases can be measured.
- Oil: specific gravity 2.1 Kg/cm 2 = 00.7*0.001*30*100 = 0.7 Kg/cm3
- Water: specific weight 0.3 Kg/cm 2 = 00.1*0.001*30*100 = 1.0 Kg/cm3
- Mercury: Specific gravity 40.8 Kg/cm 2 = 13.6 * 0.001 *30 * 100 = 13.6 Kg/cm3
What is the height drop of the pump?
As the fluid passes through the pipes, filter or valves and due to the friction with their internal walls, the amount of fluid flow and as a result the pumping height decreases to some extent, which is called height drop. Like the current of electricity, the current drop inside the cable increases with the increase of current (amps). As the speed of the fluid flow increases, the flow rate decreases and therefore the pumping height decreases. Therefore, as the fluid passes through more pipes, filters, and valves, the drop in height increases accordingly.
What is the specific gravity of pump fluid?
The specific mass of a fluid or liquid means the weight of that fluid/liquid in a specific measurement unit, which is usually based on Kg/dm measurement units. 3 or Kg/l is measured. It should be mentioned that every 1dm 3 It is equal to 1 liter.
Note: According to the relationship between the flow rate and the pumping height, the pumps can be divided into the following groups:
- Pumps with low flow rate and high pumping height (piston and rotary pumps and small centrifuges)
- Pumps with normal flow rate and height (centrifuges)
- Pumps with high flow rate and pumping height (pumps with impellers and Helio Centrifugal)
- Centrifuges or Heliocentrifugal or pumps with propeller-shaped propellers move in rotation and its rotation speed is calculated in rpm. In this category of pumps, with the change of the flow rate, the pump’s load does not change and the pumping height remains constant. Therefore, in order to change the working mode of the pump, the rotation speed of the motor must be changed.
What is the output power of the pump?
The amount of power (energy) introduced into the fluid by the pump is called the output power of the pump, which depends on three factors: flow rate, height and weight of the fluid.
For example, the output power of the pump used to pump gasoline is much lower than the output power of the pump used to pump sulfuric acid because the weight of both fluids is different. All pumps are able to pump fluids with the help of electric motors or motors installed inside the device itself. The power required by the pump to operate and pump fluids is called power consumption.
What is the power consumption of the pump?
The power input to the pump by the motor and its transfer to the fluid is called the power consumption of the pump. Due to factors such as fluid friction with the pipes or natural hydraulic drops in the device itself, the output power of the pump is always lower than its consumption power, which is mostly less than one and is calculated as a percentage, which is called the pump efficiency percentage. .
Pump efficiency
By dividing the output power of the pump by the power consumption, the efficiency of the pump is obtained. For example, a pump with an efficiency of 75% means that only the pump returns a percentage of the consumed power and 25% of it is wasted due to fluid friction with pipes and other devices or heat inside the pipe and device. As a result, the higher the pump efficiency, the lower the power consumption percentage. Therefore, its energy consumption cost is lower.
If the output power of two pumps is equal to 1 HP, while the efficiency of the first pump is 50% and the other is 60%, we conclude that the amount of power required to provide the output power of 1 HP is 2 HP for the first pump and only 1.67 HP for the second pump. is. So, as a result, the most important parameter to determine the quality of the device and the amount of energy saving is the efficiency parameter.
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