Factors Affecting Several Important Characteristic Curves of Centrifugal Pump

Category: Water pump knowledge

2024-06-07

1. Factors Affecting the Characteristic Curve of Centrifugal Pump

The characteristic curve of a centrifugal pump is related to many factors, such as the viscosity and density of the liquid, the width of the impeller outlet, the angle of the blade and the number of blades and the shape of the pressure chamber of the centrifugal pump will have an impact on the characteristic curve of the centrifugal pump.

1. Influence of impeller outlet diameter on performance curve

In the case of other impeller geometry is the same, if you change the outlet diameter of the impeller, the characteristic curve of the centrifugal pump moves in parallel. According to this characteristic, the pump manufacturer and the user unit can change the performance range of a pump by turning the outer diameter of the centrifugal pump impeller, so that the performance of the pump is more suitable for the actual operation needs. For example, a centrifugal circulating pump in a factory has a high operating pressure. In order to reduce the pressure, the outer diameter of the impeller is turned from 270mm to 250mm. Under the same flow rate, the pressure drops and the motor current of the feed pump decreases, thus meeting the operation requirements.

2. Relationship between speed and performance curve

The same centrifugal pump transport the same kind of liquid, the relationship between the pump performance parameters and speed is:

Q1/Q2 = n1/n2       

H1/H2 = (n1/n2)2    

Nl/N2 = (n1/n2)2

Definition of Characteristic Curve of 2. Centrifugal Pump

When the speed n is constant, the functional relationship between head (H), shaft power (N), efficiency (η) and allowable suction vacuum height (Hs) with flow rate (Q) is listed, namely: H = f(Q);N = F(Q);Hs = Ψ(Q);η = φ(Q), we use these equations to express the relationship with the curve, which is called the characteristic curve of the centrifugal pump.

The characteristic curve of centrifugal pump is the external manifestation of the movement law of liquid in the pump. These three curves need to be based on the test method (using the measuring device of centrifugal pump characteristic curve, gradually open the outlet valve of the pump to change its flow rate, measure a series of flow rate and corresponding lift and shaft power, and then draw the H-Q, N -Q, η-Q curves on the same coordinate paper, that is, the characteristic curve of a certain type of centrifugal pump at a certain speed), different pump characteristic curves are different, and the characteristic curve of the pump is provided by the equipment manufacturer. Strictly speaking, each pump has a specific characteristic curve.

On the pump characteristic curve, a set of corresponding head, shaft power and efficiency values can be found corresponding to any flow point, and this set of corresponding parameters is usually called the working condition, and a set of working conditions corresponding to the highest efficiency point is called the best working condition.

In production practice, the operating point of the pump is determined by the characteristic curve of the pipeline and the characteristic curve of the pump (M operating point, see the figure below). In the selection and use of the pump, the pump in the high efficiency area to ensure the operation of the economy and safety.

Six steps of water pump maintenance

1, check the pump body and pulley for wear and damage, if necessary, should be replaced. Check whether the water pump shaft is bent, the degree of journal wear, and whether the shaft end thread is damaged. Check whether the blade on the impeller is broken and whether the shaft hole is seriously worn. Check the wear degree of water seal and bakelite gasket. If the wear degree exceeds the service limit, replace it with a new one. Check the wear of the bearing, the available table to measure the bearing clearance, such as more than 0.10mm, should be replaced with a new bearing.

2. After the water pump is taken out, it can be decomposed in sequence. After decomposition, the parts should be cleaned and checked one by one to see if there are defects such as cracks, damage and wear. If there are serious defects, they should be replaced.

3. Repair of water seal and seat: If the water seal is worn and grooved, it can be polished with emery cloth. If it is worn too much, it should be replaced. If there are rough scratches on the water seal seat, it can be repaired with a flat reamer or on a lathe. Replace the new water seal assembly during overhaul.

4. Welding repair is allowed when the pump body has the following damages: the length is within 30mm, and the crack does not extend to the bearing seat hole; The flange joined with the cylinder head has a broken part; The oil seal seat hole is damaged. The bending of the water pump shaft must not exceed 0.05mm, otherwise it should be replaced. Damaged impeller blades should be replaced. Water pump shaft bore serious wear should be replaced or repair the sleeve.

5. Check whether the water pump bearing rotates flexibly or has abnormal noise. If there is any problem with the bearing, it should be replaced.

6. After the water pump is assembled, turn it by hand. The pump shaft should be free of jamming, and the impeller and the pump casing should be free of friction. Then check the water pump displacement. If there is a problem, check the cause and eliminate it. If the water pump fails, the coolant will not be able to reach the corresponding place, and its performance will not be effectively exerted, which will eventually affect the working condition of the engine. Therefore, it is necessary to strengthen the inspection of the pump.

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