Basic of Centrifugal and Positive Displacement Pump
Module CP-1 Knowledge about pumps
Basic of Centrifugal and Positive Displacement Pump
in our daily life Often see the natural movement of liquids such as waterfalls flowing from high valleys to low flows to combine with rivers and streams. or even pouring drinking water into a glass must rely on the force acting on the fluid or simply say is that the liquid flows from high to low and flows from a point of high pressure to a point of low pressure But on the other hand, if you want the liquid to flow from low to high. Or wanting the liquid to flow from one point to another at the desired flow rate requires a device to help, that is, a pump (Pump), which is a mechanical tool that serves to add energy to the liquid. To allow the liquid to flow through a closed pipe system from one point to another as needed. The energy that can be added to the liquid comes from motors, engines, wind power, human power, or other energy.
pump classification can be divided into several types Here, divided according to the nature of the drive of the liquid in the pump, which is divided into 2 types: 1. Non-Positive Displacement Pump works without relying on the liquid replacement principle. Normally used in low pressure, high flow rates, such as centrifugal pumps and 2. Positive Displacement Pumps, working by the displacement principle of the liquid in the pumping room with the movement of the parts of the pump. pump It supplies a certain volume of fluid. per revolution of the shaft can handle higher pressure in the system well This type of pump includes Rotary type such as Gear pump, Vane Pump, Lope Pump, Screw Pump and reciprocating type. (Reciprocating) such as Diaphragm Pump, Piston Pump are in the same group.
In this article, the working principles, advantages and limitations of centrifugal pumps and positive displacement pumps are described as follows.
A centrifugal pump is a mechanical device designed to move a fluid by transferring circulating energy from one or more driven rotors or impellers. The liquid flows into an impeller that rotates rapidly along the axis. and was thrown out by centrifugal force along the circumference through the tip of the propeller propeller will increase speed and the pressure of the fluid to the pump delivery path The pump housing is specially designed to squeeze out the liquid from the pump inlet. sent to propeller then slow down and control the liquid before it is discharged from the pump (With this type of pump housing design, we call this type of pump a centrifugal pump according to the characteristics of the pump housing)
Working principle of the pump
The rotating parts inside the pump housing are called rotors or impellers. will cause fluid propulsion The diffuser is a stationary part. It serves to convert the velocity head to static pressure. The pumped fluid flows through the inlet channel which is parallel to the shaft axis and is thrown out along the radial direction of the impeller or rotor.
A mechanism for transmitting energy in a rotor or propeller. As a result of changes in fluid momentum causing a pressure difference within the system Causing a flow in the circumference (Tangentail flow) which results in the centrifugation force (Centrifugul force) up and with this force will cause the flow from the center of the impeller to the circumference in all directions out through the pipeline. Therefore The expelled fluid has a direction of flow caused by the sum of the two forces.
Impeller (Impeller) is an important component of a centrifugal pump consisting of a series of curved impellers. The impeller is as if sandwiched between two discs (closed impeller) and for solid liquids it is best to use an open impeller or semi-open impeller as shown in Fig. 1.
The basis of the pump housing has two design features : 1. Volute ( Volute ) and 2. Diffuser ( Diffuser ) The purpose of the design of both types is for converting the flow of liquid. to pressure-controlled transmission. In the volute structure, the impeller is offset. This creates an efficient curved cone with increased cross-sectional area upon reaching the pump outlet. This design increases the fluid pressure to
The same basic principles apply to the diffuser design, but a guide vane is attached around the pump housing, also controlling the direction of the fluid flow. In order to cause a higher pressure, in this case, the pressure of the fluid will increase. As the fluid is expelled between a series of stationary impellers surrounding the impeller (Fig. 3), the diffuser design can be tailored to the specific application. So it’s more efficient. Spiral boxes are suitable for applications involving highly viscous solids or liquids. To avoid the limitations of the diffuser impeller, the asymmetry of the volute design may result in the impeller and the wear of the drive shaft due to the radial force acting on the impeller is greater than that of the diffuser design.
Centrifugal pumps work by transferring renewable energy from one or more driven rotors. called propeller The propeller will increase the speed. and the pressure of the liquid and take it to the pump outlet with a simple design Centrifugal pumps are therefore widely used and easy to maintain.
Centrifugal pump design is a simple method. Suitable for applications involving low viscosity liquids such as water, solvents or chemicals as well as general applications involving water supply, circulation, irrigation or chemical transfer in petrochemical plants. And for applications involving highly viscous fluids, positive displacement pumps should be used, such as thick oils. and viscous solution especially at high pressure but requires a constant flow rate throughout
Positive displacement pumps work on the principle of displacement of the fluid in the pumping chamber by the movement of pump components. This type of pump supplies a certain fluid with a certain volume. per revolution of the shaft which can handle the increased pressure in the system well The operation of this type of pump uses the compression principle. And continuously squeeze the liquid, the flow rate is constant throughout Although the outlet pressure (Discharge) will be variable – variation.
Positive displacement pumps can be classified into two types: Rotary and Reciprocating.
1.) Rotary pump Rotary pump works by displacing the liquid inside the chamber of the pump. with the movement of the parts which rotates to cause a pressure difference within the system. The liquid is sucked in and compressed, creating a higher pressure and then discharged through the discharge side. Such rotating parts are known as rotors. Will cause a constant replacement of fluid. causing the fluid flowing through the pump to have a constant flow rate at all times This type of pump has a lower pumping rate than other pumps due to its low liquid displacement rate, typically 80-85% efficiency depending on friction losses. and characteristics of the pumped fluid Rotary pumps can be divided into two types: Gear pump and Screw pump.
1.1) Gear pumps are widely used. The liquid is pumped at a constant rate. Make the flow continue all the time. Suitable for pumping high viscosity liquids. Inside the housing consists of 2 gears that rotate together, which are easy to repair, clean and can be easily disassembled. The performance of this type of pump is quite high when working with fluids that qualify as lubricants.
1.2) Screw rotary pump (Screw pump) within this rotary screw pump (Screw) inside will look like a rotating screw. The twisting of the threads creates a pressure difference within the system. Makes it possible to drive the fluid to move.
2.) Reciprocating or reciprocating pump. (Reciprocating pump)Reciprocating pumps are characterized by moving back and forth with the piston acting to compress the fluid inside the cylinder to increase the pressure. With its back-and-forth motion, it is suitable for pumping small amounts of fluid. but want a high head in the system The fluid used in this type of pump must be clean enough to not accelerate wear of the moving parts inside the cylinder. Each compression of the fluid is rhythmic. According to the back and forth motion of the piston with incoherent motion. thus causing the flow of the fluid to look like a pulsation
For example, this type of pump is A diaphragm pump (Diaphragm pump) This type of pump has a diaphragm plate made of non-metallic. which is flexible And strong will serve to suck. and compressing the fluid to a higher pressure The diaphragm is fixed in place. Popular with applications where the rate of pumping is not much. and the fluid contains suspended solids In general, when choosing a pump Can be divided into 2 main types due to the viscosity of the liquid that will determine which are centrifugal pumps and positive displacement pumps. Centrifugal pumps are often specified for use. For pumping low viscosity liquids between 0. 1 – 200 cP and found that when using centrifugal pumps with high viscosity liquids, the efficiency of the centrifugal pump is greatly reduced. due to greater resistance to flow within the pump itself It was found that in general factories, 90% of the pumps used are centrifugal pumps. However, there are many applications that require positive displacement displacement pumps. Additional limitations of centrifugal pumps are Unlike positive displacement pumps, centrifugal pumps cannot generate suction when the pump housing is not full (run dry). Therefore, the use of centrifugal pumps must be preliminarily prepared. by filling the liquid that needs to be pumped into the pump housing before pumping For this reason, centrifugal pumps are also not suitable for any application where intermittent fluid supply is involved. In addition, if the required pressure of the system varies. A centrifugal pump will not be able to create a variable pressure by maintaining a constant flow rate. Therefore, in applications where flow rate accuracy is required A positive displacement displacement pump should be used.