164 Technical Issues Related To Pumps(164-1-15)

A pump is a machine that transports fluid or pressurizes fluid. It transfers the mechanical energy of the prime mover or other external energy to the liquid, increasing the energy of the liquid. The pump is mainly used to transport liquids such as water, oil, acid and alkali liquids, emulsions, suspoemulsions and liquid metals. It can also transport liquid, gas mixtures and liquids containing suspended solids. Pumps can usually be divided into three categories: positive displacement pumps, dynamic pumps and other types of pumps according to their working principles. In addition to classification according to working principles, they can also be classified and named according to other methods. For example, according to the driving method, it can be divided into electric pumps and water wheel pumps; according to the structure, it can be divided into single-stage pumps and multi-stage pumps; according to the use, it can be divided into boiler feed pumps and metering pumps; according to the properties of the transported liquid, it can be divided into Water pumps, oil pumps and mud pumps, etc. According to the structure with or without a shaft, it can be divided into linear pumps and traditional pumps. Water pumps can only transport flows with fluid as the medium and cannot transport solids.

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We often encounter some problems when using pumps. Shanghai Jiushi Pump Industry has compiled 164 product problems about pumps:

A1. What is a pump?

Q1: A pump is a machine that converts the mechanical energy of the prime mover into energy for pumping liquid.

A2. What is power?

Q2: The work done per unit time is called power.

A3. What is effective power?

Q3: In addition to the energy loss and consumption of the machine itself, the actual power obtained by the liquid through the pump per unit time is called effective power.

A4. What is shaft power?

Q4: The power transmitted by the motor to the pump shaft is called shaft power.

A5. Why is it said that the power transmitted by the motor to the pump is always greater than the effective power of the pump?

Q5:1). When the centrifugal pump is running, part of the high-pressure liquid in the pump will flow back to the inlet of the pump, or even leak out of the pump, so part of the energy must be lost;

2). When the liquid flows through the impeller and pump casing, changes in flow direction and speed, as well as mutual collisions between fluids, also consume part of the energy;

3). Mechanical friction between the pump shaft, bearings and shaft seals also consumes part of the energy; therefore, the power transmitted by the motor to the shaft is always greater than the effective power of the shaft.

A6. What is the overall efficiency of the pump?

Q6: The ratio of the effective power of the pump to the shaft power is the total efficiency of the pump.

A7. What is the flow rate of the pump? What symbol is used?

Q7: Flow refers to the amount of liquid (volume or mass) flowing through a certain section of the pipeline per unit time. The flow rate of the pump is represented by "Q".

A8. What is the head of the pump? What symbol is used?

Q8: Lift refers to the increment of energy obtained by unit weight of fluid. The head of the pump is represented by "H".

A9. What are the characteristics of chemical pumps?

Q9: 1). Can adapt to chemical process requirements; 2). Corrosion resistance; 3). Resistance to high and low temperatures; 4) Wear resistance and erosion resistance; 5) Reliable operation; 6) No or little leakage; 7) Ability to transport Critical state liquid; 8) Anti-cavitation properties

A10. How many categories are commonly used mechanical pumps divided into according to their working principles?

Q10: 1) Vane pump. When the pump shaft rotates, various impeller blades are driven to give centrifugal force or axial force to the liquid, and the liquid is transported to pipes or containers, such as centrifugal pumps, vortex pumps, mixed flow pumps, and axial flow pumps. 

2) Positive displacement pump. Pumps that utilize continuous changes in the volume of the pump cylinder to transport liquids, such as reciprocating pumps, piston pumps, gear pumps, and screw pumps; 

3) Other types of pumps. For example, electromagnetic pumps that use electromagnetism to transport liquid conductors; pumps that use fluid energy to transport liquids, such as jet pumps, air lifters, etc.

A11. What should be done before chemical pump maintenance?

Q11: 1) Machinery and equipment must be stopped before maintenance, cooling, pressure relief, and power supply cut off; 

2) Machinery and equipment containing flammable, explosive, toxic, and corrosive media must be cleaned, neutralized, and replaced before maintenance Construction can only be carried out after passing the analysis and testing; 

3) For maintenance of equipment, machines, and pipelines with flammable, explosive, toxic, corrosive media or steam, the material inlet and outlet valves must be cut off and blind plates must be added.

A12. What process conditions should be met before chemical pump maintenance?

Q12: 1) Stop; 2) Cool down; 3) Relieve pressure; 4) Cut off power supply; 5) Replace

A13. What are the general mechanical disassembly principles?

Answer: Generally speaking, it should be disassembled in order from the outside to the inside, from top to bottom, and the whole parts should be disassembled as a whole as much as possible.

A14.What are the power losses in centrifugal pumps?

Q14: There are three types of losses: hydraulic loss, volume loss, and mechanical loss. 1) Hydraulic loss: When the fluid flows in the pump body, if the flow path is smooth, the resistance will be smaller. If the flow path is rough, the resistance will be greater. The water flows into the rotating When the impeller or water flow comes out of the impeller, collision and vortex will also occur, causing losses. The above two types of losses are called hydraulic losses. 

2) Volume loss: The impeller is rotating, but the pump body is stationary. A small part of the fluid in the gap between the impeller and the pump body flows back to the impeller inlet; in addition, a part of the fluid flows back from the balance hole to the impeller inlet, or Leakage from shaft seal. If it is a multi-stage pump, there will also be some leakage from the balance plate. These losses are called volume losses; 3) Mechanical losses: When the shaft rotates, it will rub against the bearings, packing, etc., the impeller rotates in the pump body, and the front and rear cover plates of the impeller will rub against the fluid, all of which consume a part of the power. These are due to mechanical Losses caused by friction are always mechanical losses.

A15. In production practice, what is the basis for balancing the rotor?

Q15: Depending on the number of revolutions and structures, static balancing method or dynamic balancing method can be used. The static balance of a rotating body can be solved by the static balance method. Static balance can only balance the imbalance of the rotating center of gravity (i.e. eliminate the moment), but cannot eliminate the unbalanced couple. Therefore, static balancing is generally only applicable to disk-shaped rotating bodies with relatively small diameters. For rotating bodies with relatively large diameters, dynamic balancing problems are often more common and prominent, so dynamic balancing must be performed.

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