Due to the increasing penetration of hydraulic systems in various industries, the existence of pumps with different power and pressures is needed more than before. The pump, as the heart of the hydraulic system, converts the mechanical energy supplied by the electric motors, internal combustion and به into hydraulic energy. In fact, the pump in a hydraulic or pneumatic cycle increases the energy of the fluid to become the desired work at the required location of this added energy.
Atmospheric pressure due to the relative vacuum created due to the operation of the mechanical components of the pump, forces the fluid to move towards its inlet duct to be driven by the pump to other parts of the hydraulic circuit.
The volume of high pressure oil delivered to the hydraulic circuit depends on the capacity of the pump and therefore on the volume of fluid displaced in each cycle and the number of revolutions of the pump. Pump capacity is expressed in gallons per minute or liters per minute.
A noteworthy point in fluid suction is the permissible vertical height of the pump relative to the free surface of the fluid. In the case of oil, this height should not be more than 10 meters, because due to the relative vacuum, if the height is more than 10 meters, the oil boils Liquid, oil vapor enters the pump and will disrupt the work cycle. But there is no limit to the height of the pump outlet and only the power of the pump can determine it.
Types of pumps:
1- Negative displacement pumps (dynamic pumps)
Negative displacement pumps: They do not have the ability to withstand high pressures and are rarely used in the hydraulic industry and are usually used as primary fluid transfer. They are used from one point to another. In general, these pumps are suitable for low pressure and high flow systems whose maximum compressive capacity is limited to 250 psi to 3000 si. Centrifugal and axial pumps are a practical example of non-positive displacement pumps.
2- Positive displacement pumps
Positive displacement pumps: In these pumps, a certain amount of fluid is sent to the outlet for each rotation of the shaft and has the ability to overcome the outlet pressure and friction. These pumps have many advantages over non-positive displacement pumps such as smaller dimensions, high volumetric efficiency, good flexibility and ability to work at high pressures (even more than psi)
a) Positive displacement pumps from Building opinion:
pumps 2- Vane
pumps 3- Piston pumps
b) Pumps with positive displacement in terms of displacement rate:
1- Pumps with fixed
displacement 2- Pumps with displacement Variable
We need to know that pumps do not create pressure but generate flow. In fact, in a hydraulic system, the pressure indicates the amount of resistance to the pump outlet. If the outlet is at a pressure of one atmosphere, the outlet pressure of the pump will not exceed one atmosphere at all. 100 atmospheres are created in the fluid.
The efficiency of a pump generally depends on the tolerances and accuracy used in the construction, the mechanical condition of the components and the pressure balance. In the case of pumps, three types of efficiency are calculated:
1- Volume efficiency which determines the amount of leakage in the pump and is obtained from the following equation
(theoretical flow rate that the pump should produce / actual flow rate of the pump) = volume
efficiency 2- efficiency A mechanism that determines the amount of energy lost due to factors such as friction in the bearings and components involved as well as turbulence in the fluid.
Mechanical efficiency = (real power given to the pump / theoretical power required for the pump to work)
3- Total efficiency that determines the total energy loss in a pump and is equal to the product of mechanical efficiency in volume efficiency.
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