- June 5, 2022
Imen Datis Asia Co
In a positive displacement pump, a certain amount of fluid is drawn in and trapped between two pieces due to water suction. Then, by moving one of these pieces, the desired liquid is pressurized and then, as soon as the liquid pressure reaches a certain value, it exits the pump.
These types of pumps are devices that transfer energy to a fluid periodically. The driving force of these types of pumps is often provided by electric motors.
In this type of pump, the rotational motion of the crankshaft is converted into a reciprocating motion of a piston in a cylinder. As the piston moves backward, suction is created in the cylinder, and as a result, liquid enters the cylinder through an inlet valve. As the piston moves forward, the inlet valve closes and the liquid is directed out through the outlet valve.
As mentioned, a positive displacement pump is a type of pump used to transport fluids.
In contrast to other pumps, such as centrifugal pumps, which operate on the principle of fluid circulation, a positive displacement pump moves fluid from one place to another by creating a direct and repeated displacement of the fluid.
The operation of a positive displacement pump is based on two main parts: the displacement assembly and the key assembly. The displacement assembly consists of one or more moving members that create the flow of fluid by displacing and compressing it. The key assembly consists of a system of special valves or keys that move the fluid flow in a uniform direction and prevent it from reversing.
A type of positive displacement pump is a piston pump that uses one or more pistons to apply reciprocating motion to a fluid. As the piston moves outward, the volume of the fluid inside it increases and the pressure decreases.
Instead, as the piston moves inward, the volume of the fluid decreases and the pressure increases. This alternating action of displacing and compressing the fluid helps move it through the system.
Positive displacement pumps are suitable for applications that require constant and controllable flow and pressure due to their special characteristics. This type of pump is used in various industries such as oil and gas, petrochemical, food and pharmaceutical, chemical and other manufacturing industries.
The following types of positive displacement pumps can be mentioned:
Positive displacement pumps in terms of displacement:
1- Fixed displacement pumps
2- Variable displacement pumps
In a fixed displacement pump, the amount of fluid pumped per revolution of the shaft is constant, while in variable displacement pumps, the above amount can be increased or decreased by changing the relationship between the pump components. It is to increase. These pumps are also called variable flow pumps.
Recommended article: What is a lobe pump and what is its use?
This type of direct displacement pump is widely used in the construction of high-pressure sprinklers. The most important application of this type of pump is washing in various applications, including car washes, cement tank industries, etc.
A piston pump consists of a piston cylinder, an inlet valve, and an outlet valve.
The pump piston moves up and down in the form of a handle, one side of which is placed on a rotating wheel.
When the piston moves upwards, the outlet valve is closed due to suction and the force of the return flow from the outlet port, and due to the suction force created inside the cylinder, the inlet valve opens and the liquid is sucked into the pump chamber. When the piston moves downwards, the inlet valve closes and the outlet valve opens, and the fluid trapped in the chamber and under the pressure of the piston is transferred to the outlet port. Repeating this action causes the fluid to be transferred from one place to another.
These pumps are often used to inject chemicals. (Injecting chlorine into swimming pools and injecting chemicals into boiler feed water are some of the applications of diaphragm pumps.)
In these pumps, the amount of fluid injected can be adjusted to the required amount by changing the movement of the diaphragm.
The most important feature of these pumps is that they are leak-free.
The working principle of this type of pump is based on the constant rotation of one or more rotors inside a chamber. As the rotors rotate, the pressure decreases on one side and as a result, the fluid enters the suction chamber and gets trapped between the rotor blades.
The rotation of the rotors causes the fluid between them to be compressed (its pressure increases) and pushed towards the outlet.
This type of pump uses lobe-shaped parts for pumping. The function of this pump is similar to an external gear pump.
These pumps are available in single-lobe, double-lobe, triple-lobe and quadruple-lobe designs.
In lobe pumps, the size of the pumped particles can be much larger than in other positive displacement pumps.
A positive displacement screw pump uses one or more screws to transport liquid or solids in the direction of the screw axis. The screw rotates in a cylindrical housing and directs the material to the pump outlet.
This type of pump has the advantage that the pumped fluid moves axially, without loss of flow velocity, without turbulence, which eliminates the possibility of foaming with viscous fluids.
Non-positive displacement pumps (or dynamic pumps) are a type of acceleration pump in which kinetic energy is added to the fluid as the flow rate increases. This increase in energy is converted into potential energy (pressure) if the velocity is reduced before the pump exits or the fluid exits the pump into the discharge pipe. As you can see, their operation is the opposite of positive displacement pumps, which is why they are called non-positive displacement pumps and not negative displacement pumps.
Difference in pressure
Difference in efficiency
Difference in viscosity
Difference in performance
Differences in production flow
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