pump
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What is a pump in engineering?
In engineering, a pump is a device that moves fluids (liquids or gases) by suction or pressure. Pumps are essential in various applications, including transporting liquids in pipes, rivers, and channels, and are confined by dams and tanks.
Pumps are classified based on how energy is transferred to the fluid, using methods such as volumetric displacement, kinetic energy addition, or electromagnetic force. Positive displacement pumps mechanically move relatively low fluid volumes at high pressure, while kinetic pumps propel high volumes at low pressure by using a rotating impeller to impart kinetic energy to the fluid.
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What are pumps used for?
Pumps serve various engineering purposes, transferring energy to fluids through methods like volumetric displacement, kinetic energy addition, or electromagnetic force. They are essential in water distribution systems, moving water from low-lift pumps at treatment plants to high-lift pumps that discharge treated water into mains, and also include booster pumps and well pumps.
Positive displacement pumps, such as reciprocating and rotary pumps, manage a set volume per cycle, while kinetic pumps use a rotating impeller to increase fluid pressure. Electromagnetic pumps, used for fluids that are good electrical conductors, apply electromagnetic force to facilitate flow and are often used to pump liquid metals for cooling nuclear reactors. In petroleum production, pumps provide artificial lift to extract crude oil from wells.
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How does a basic pump work?
Pumps move fluids (liquids or gases) by imparting energy through various methods. The three basic types are positive displacement, kinetic energy addition, and electromagnetic force.
Positive displacement pumps use mechanical methods to move fluids, such as pistons or gears. Kinetic pumps, like centrifugal pumps, increase fluid velocity using a rotating impeller. Electromagnetic pumps use magnetic fields and electric current to pump conductive fluids.
The characteristics of a pump are the required inlet pressure, the capacity against a given total head, and the percentage efficiency for pumping a particular fluid.
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What are the main types of pumps?
Pumps are classified based on how energy is imparted to a fluid, with the main types being volumetric displacement, addition of kinetic energy, and electromagnetic force.
- Positive Displacement Pumps These pumps move a specific volume of fluid per cycle and include reciprocating (piston, plunger, and diaphragm types) and rotary pumps (gear, lobe, screw, vane, and cam types).
- Kinetic Pumps These pumps impart kinetic energy to the fluid using a rotating impeller. Types include centrifugal (radial, axial, and mixed flow) and regenerative pumps.
- Electromagnetic Pumps These pumps use electromagnetic force to pump electrically conductive fluids by passing a current through the fluid in a magnetic field.
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How does a centrifugal pump differ from a positive displacement pump?
Centrifugal and positive displacement pumps differ in how they move fluids. Centrifugal pumps use a rotating impeller to add kinetic energy to fluids, making them suitable for high-volume, low-pressure applications like water supply, irrigation, and sewage disposal. The flow rate in these pumps varies with pressure.
Positive displacement pumps, such as piston, plunger, and gear pumps, displace a fixed volume of fluid with each cycle, making them ideal for low-volume, high-pressure applications. Their flow capacity remains constant regardless of system pressure.
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What are some common uses of pumps in everyday life and industry?
Pumps have numerous applications across daily life and various industries. In homes, well pumps supply water, while diaphragm pumps handle liquids in appliances. Industries use low-lift pumps to transfer water to treatment plants, and high-lift pumps discharge treated water into mains. Electromagnetic pumps cool nuclear reactors, and hydraulic ram pumps are used in domestic water systems. In agriculture, pumps are essential for irrigation systems, ensuring efficient water distribution for crop production.
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pump, a device that expends energy in order to raise, transport, or compress fluids. The earliest pumps were devices for raising water, such as the Persian and Roman waterwheels and the more sophisticated Archimedes screw (q.v.).
The mining operations of the Middle Ages led to development of the suction (piston) pump, many types of which are described by Georgius Agricola in De re metallica (1556). A suction pump works by atmospheric pressure; when the piston is raised, creating a partial vacuum, atmospheric pressure outside forces water into the cylinder, whence it is permitted to escape by an outlet valve. Atmospheric pressure alone can force water to a maximum height of about 34 feet (10 metres), so the force pump was developed to drain deeper mines. In the force pump the downward stroke of the piston forces water out through a side valve to a height that depends simply on the force applied to the piston.
Classification of pumps.
Pumps are classified according to the way in which energy is imparted to the fluid. The basic methods are (1) volumetric displacement, (2) addition of kinetic energy, and (3) use of electromagnetic force.
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A fluid can be displaced either mechanically or by the use of another fluid. Kinetic energy may be added to a fluid either by rotating it at high speed or by providing an impulse in the direction of flow. In order to use electromagnetic force, the fluid being pumped must be a good electrical conductor. Pumps used to transport or pressurize gases are called compressors, blowers, or fans. Pumps in which displacement is accomplished mechanically are called positive displacement pumps. Kinetic pumps impart kinetic energy to the fluid by means of a rapidly rotating impeller.
Broadly speaking, positive displacement pumps move relatively low volumes of fluid at high pressure, and kinetic pumps impel high volumes at low pressure.
A certain amount of pressure is required to get the fluid to flow into the pump before additional pressure or velocity can be added. If the inlet pressure is too small, cavitation (the formation of a vacuous space in the pump, which is normally occupied by liquid) will occur. Vaporization of liquid in the suction line is a common cause of cavitation. Vapour bubbles carried into the pump with the liquid collapse when they enter a region of higher pressure, resulting in excessive noise, vibration, corrosion, and erosion.
The important characteristics of a pump are the required inlet pressure, the capacity against a given total head (energy per pound due to pressure, velocity, or elevation), and the percentage efficiency for pumping a particular fluid. Pumping efficiency is much higher for mobile liquids such as water than for viscous fluids such as molasses. Since the viscosity of a liquid normally decreases as the temperature is increased, it is common industrial practice to heat very viscous liquids in order to pump them more efficiently.
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