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Conditions for using a centrifugal pump

Conditions for using a centrifugal pump
Pump with two discharge nozzles

In order for the centrifugal pump to work as efficiently as possible, it is necessary to take into account certain conditions. To consider these conditions in more detail, let us use the figure.


The figure shows a pump with two exhaust nozzles. Imagine that it has only one nozzle, located vertically, with the friction of the pipe being ignored.


Taking into account the diameter of the impeller and the rotation of the shaft at specified speeds, this centrifugal pump will push the liquid up to the maximum height.
This height is the maximum head at zero flow. Pressure is the force created by its blades or pump pistons, necessary to push through water or gas. You can also use a synonym for the word pressure, pressure. It is worth recalling that the pressure of 10.2 meters of fresh water at 20°C is one bar.


The head is determined by the diameter of the impeller and the rotational speed of the shaft per minute. If you increase one of these parameters, then the head at zero feed will be larger. Note: that in this case the liquid will not flow out of the pipe, in other words, the liquid will not have the flow velocity.


If you rotate the outlet nozzle horizontally and ignore the pipe friction, the fluid would exit at the maximum speed.


It is also obvious that as the head increases, the speed will decrease, too, if the fluid velocity is increased, the head will decrease. This centrifugal pump can provide fluid velocity, head, or a combination thereof. When it comes to speed, we express it in the speed of movement, measured in meters per second.


If the outlet nozzle is rotated from vertical to horizontal, the liquid will outline the pump curve. The pump curve does not show the flow velocity, it shows the power and speed of the pump in cubic meters per hour. The shape of the curve will be determined by the shape of the impeller.


Pump speed ratio is the term used to determine the shape of the impeller. The shape of the impeller of most popular pumps used in the processing industry is of the "Francis" type. This name was received in honor of the Anglo-American engineer James Francis, who developed it.


The values of the coefficient of speed

If the pumped medium differs from fresh water, the specific gravity of this liquid must be considered in order to determine the correct pressure. The term specific gravity serves to determine the weight of the liquid. Water gets a value of 1, so if the liquid floats in fresh water, its specific gravity will be less than 1. If the liquid is drowned in fresh water, the specific gravity will be greater than 1.


In any pump, there is an ideal combination of head and speed. When the pump reaches this combination, it means that it works at the optimum efficiency point (BEST EFFICIENCY POINT - B.E.P). It is very important to remember that the pump pumps the difference between the injection and suction valves.


The optimum efficiency point is the point at which the shaft deflection is minimal, and the input power is closest to the output power. In other words, the shaft does not move, and less energy is used to operate the pump. This point is between 80% and 85% of the pump power.


Look at the image below.

Pump connection configurations

Figure "A" shows two pumps connected in series. If these pumps are the same size, this will double the load per pump, but at the same time its performance will remain. If the pumps are of different sizes, then the power limit of the smallest pump will be limited, and the head will be added together.


In figure "B" two pumps connected in parallel. In this configuration, the power of one pump is doubled, but the head remains the same.


Thus, in order to use the centrifugal pump as efficiently as possible, it is necessary to take into account all the conditions under which the pump reaches the optimum efficiency point.


Experts of AvtokomTehnolodgy group of companies will help you to choose the right pump with the necessary parameters for supply and pressure of the working environment to solve your problems!


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