Full analysis of horizontal multistage centrifugal pump knowledge
Horizontal multistage centrifugal pump knowledge
Working principle of centrifugal pump
The centrifugal pump relies on the rotating impeller to generate force on the liquid to transfer the mechanical energy of the prime mover to the liquid. Due to the action of the centrifugal pump, the velocity energy and pressure energy of the liquid are increased in the process of flowing from the impeller inlet to the outlet. The liquid discharged by the impeller passes through the extrusion chamber, and most of the velocity energy is converted into pressure energy, and then transported out along the discharge pipeline. At this time, the impeller inlet forms a vacuum or low pressure due to the discharge of the liquid. The liquid in the suction pool is pressed into the impeller inlet under the action of the liquid surface pressure (atmospheric pressure), so the rotating impeller continuously inhales and discharges the liquid.
Partial explanation of centrifugal pump terms
Why is it called a centrifugal pump?
The concept of centrifugation
Centrifugation is actually a manifestation of the inertia of an object, such as the water droplets on an umbrella. When the umbrella rotates slowly, the water droplets will rotate with the umbrella. This is because the friction between the umbrella and the water droplets acts as the centripetal force for the water droplets. But if the umbrella rotates faster, the friction is not enough to make the water droplets move in a circle, then the water droplets will break away from the umbrella and move to the outer edge, just like using a rope to pull a stone to make a circle. If the speed is too fast, the rope will break and the stone will fly out. This is the so-called centrifugal.
Centrifugal pumps are designed based on this principle. The high-speed rotating impeller blades drive the water to rotate and throw the water out, thereby achieving the purpose of transportation.
Lift
The lift of a water pump refers to the height to which the water pump can lift water, usually represented by the symbol H, and its unit is meter. The lift of a centrifugal pump is based on the center line of the impeller and consists of two parts. The vertical height from the center line of the water pump impeller to the water surface of the water source, that is, the height to which the water pump can suck up water, is called the suction lift, or suction lift for short; the vertical height from the center line of the water pump impeller to the water surface of the outlet pool, that is, the height to which the water pump can press up water, is called the pressure lift, or pressure lift for short. That is, water pump head = suction head + pressure head. It should be pointed out that the head indicated on the nameplate refers to the head that the water pump itself can generate. It does not include the loss head caused by the friction resistance of the pipe water flow. When selecting a water pump, be careful not to ignore it. Otherwise, the water will not be pumped up.
Pump stage number
The pump stage number indicates the number of impellers and the head multiple. For example, a single-stage pump determines a certain flow rate and head. A two-stage pump is a pump with two identical impellers. It will not increase the flow rate, but the head will double; there are several impellers for several stages, and the head will increase several times.
Selection of centrifugal pumps
First of all, please note:
The maximum head of a centrifugal pump: the pressure is the highest at the 0 flow point.
The head marked on the nameplate: the working point when in use. Basically, the most efficient point.
The flow adjustment range of a centrifugal pump: it is generally recommended to use between 0.7 and 1.2 times the flow marked on the nameplate.
The head adjustment range of a centrifugal pump: corresponds to the pump head-flow curve (i.e., the head range between 0.7 and 1.2 times the flow).
Six basic points
1. Characteristics of the medium: medium name, specific gravity, viscosity, corrosiveness, toxicity, etc.
2. The particle diameter and content of the medium.
3. Medium temperature: (℃)
4. Required flow
Generally, industrial pumps can ignore the leakage in the pipeline system during the process, but the impact on the flow during process changes must be considered. If an agricultural pump uses an open channel to transport water, leakage and evaporation must also be considered.
5. Pressure: suction tank pressure, drainage tank pressure, and pressure drop (head loss) in the pipeline system.
6. Pipeline system data (pipe diameter, length, type and number of pipeline accessories, geometric elevation from suction tank to pressure tank, etc.).
If necessary, the device characteristic curve should also be drawn.