1. What is the definition of chemical pump

Answer: The pump is a device that converts the mechanical energy of the prime mover (internal combustion engine, electric motor, turbine, etc.) into static pressure energy and kinetic energy to deliver the medium

2. How are chemical pumps classified

Answer: According to the working principle, it can be divided into the following categories:

Positive displacement pump: suction or discharge of liquid depends on the continuous change of working volume. Common ones include reciprocating pump, plunger pump, etc

Speed-type pump: relying on the high-speed rotation of the impeller, the energy is transferred to the liquid, which makes the liquid produce pressure and flow. According to the liquid flow, it can be divided into centrifugal pump, axial flow pump, vortex pump, etc

Other types of pumps: jet pump, air booster, etc

3. What is the working principle of centrifugal pump

Answer: When the prime mover drives the impeller to rotate at high speed, the liquid filled in the pump body is thrown from the center of the impeller to the outer edge of the impeller under the action of centrifugal force. In this process, the liquid gains energy and improves the static pressure energy. At the same time, the kinetic energy also increases as the flow rate increases. The liquid leaves the impeller and enters the pump casing. As the flow channel gradually increases, the fluid speed decreases, and part of the kinetic energy is converted into static pressure energy, and the liquid enters the pressure conduit at a high pressure. When the liquid is thrown out from the center of the blade, low pressure is caused at the center of the impeller, and the pressure at the liquid level is higher than that here. Under the pressure difference, the liquid enters the pump through the suction pipe. When the impeller keeps rotating, the liquid will be continuously sucked in from the center of the impeller and continuously discharged at a certain pressure

4. What are the main components of a centrifugal pump

Answer: Centrifugal pump is composed of pump casing, pump body, impeller, suction chamber and discharge chamber

5. What are the main performance parameters of centrifugal pump

Answer: ⑴ Flow: the amount of liquid discharged by the pump in unit time, also known as liquid delivery capacity. The unit is m3/s. M3/h or L/s are commonly used in engineering. The flow depends on the structure, size and speed

⑵ Head, also known as pump head, refers to the actual energy obtained by unit weight of liquid through the pump. Its unit can be expressed in [m liquid column]

(3) Power, the work done by the pump in unit time. The actual work obtained by the pump in unit time is also called effective power. The power obtained by the pump from the prime mover is called shaft power

(4) Efficiency, the ratio of effective power to shaft power. The efficiency is always less than 1

6. How does the cavitation phenomenon of centrifugal pump occur and what is the harm? How to prevent cavitation

Answer: When the pressure at the suction inlet of the pump drops below the saturated vapor pressure of the liquid in the pump at this temperature, the liquid will boil and form a large number of bubbles. At the same time, some gases dissolved in the liquid will also escape and form bubbles due to the pressure reduction. The bubble enters the high pressure zone with the liquid, and the bubble bursts rapidly to produce a local vacuum. Then the surrounding liquid rushes into the space occupied by the bubble at a great speed and collides with each other, making its kinetic energy immediately converted into pressure energy, and generating a high local impact force in an instant. This impact force causes great damage to the impeller, which can lead to the formation of honeycomb or sponge on the surface of the impeller. When cavitation occurs, the pump body will be impacted and vibrated, and noise will occur. The performance of the pump will deteriorate sharply, and in serious cases, the flow will be cut off and the pump will not work normally

The means to prevent cavitation are:

(1) The installation height of the pump body must be less than the allowable vacuum suction height

⑵ The effective cavitation allowance provided by the pump body installation is greater than the cavitation allowance required by the pump body

(3) When the flow rate increases, the cavitation margin also increases, and attention should be paid during operation

(4) Pay attention to the fact that the operating temperature of the transported liquid should not be too high

7. Why should the outlet valve be closed first when the centrifugal pump is started and stopped

Answer: If the outlet valve of the centrifugal pump is not closed during startup, the motor may be burnt out due to excessive startup power. Close the outlet valve, Q=0, and the required power is the smallest, which can avoid the above accidents. When stopping, if the outlet valve is not closed first and the pump is stopped suddenly, the high-pressure liquid in the discharge pipe may be flushed back into the pump, causing the impeller to reverse at high speed, resulting in damage. To protect the equipment, first close the outlet valve and then stop the motor

8. Why fill the centrifugal pump with liquid before starting

Answer: If the pump is not filled with liquid before starting, there is air in the centrifugal pump, and the density of air is much smaller than the density of liquid. The centrifugal force generated by the impeller rotation on the pump is very small, and the vacuum degree formed is also very low. The difference between the liquid level in the storage tank and the static pressure head at the pump inlet is also very small, which can not drive the liquid into the pump, causing the impeller to idle and not absorb the liquid. This is the so-called“ Gas binding” Phenomenon

9. What are the main components of reciprocating pump? What is the difference between its flow regulation method and centrifugal pump

Answer: The reciprocating pump is mainly composed of pump cylinder, plug, piston rod, suction valve and discharge valve. The flow of centrifugal pump is generally regulated by controlling the opening degree of the outlet valve, while the flow of reciprocating pump is usually regulated by changing the plug stroke and installing the return branch

10. What are the startup and shutdown steps of general centrifugal pump

Answer: ⑴ Start up (the motor was powered on before):

1) Turn for more than one week, and confirm that the rotor is not jammed

2) Check that the oil level of the oil cup is normal (more than 1/2)

3) Confirm that the outlet valve is closed and open the inlet valve

4) Exhaust the pump body and close it after passing the test

5) Open the minimum flow line valve; If there is sealing water, use sealing water

6) Start the motor, open the outlet valve after the outlet pressure is normal, and confirm that the motor pump operates normally

7) If the centrifugal pump is equipped with auxiliary oil pump, first establish oil circulation and then start the pump; The pump that needs to be warmed up must be qualified

(2) Parking:

1) Close the pump outlet valve and stop the motor; If there is an auxiliary oil pump, confirm that it starts automatically, otherwise start manually

2) If maintenance is required, the centrifugal pump shall be powered off, drained, and handed over for maintenance after the replacement is qualified

11. What are the advantages and disadvantages of centrifugal pump, reciprocating pump and rotary pump

Answer: Centrifugal pump: simple and compact structure, uniform flow, easy adjustment, small vibration, low requirements for foundation, wide application range, low head, low efficiency for viscous liquid, small flow, limited head

Reciprocating pump: high lift, fixed flow, dry suction capacity, high efficiency, can be used as metering pump; However, the flow is uneven, the structure is complex, and the transmission mechanism is provided

Rotary pump: suitable for liquid with small flow, high lift and high viscosity

12. What is the difference between the starting of centrifugal pump and gear pump

Answer: In order to reduce the starting load and avoid overloading, the outlet valve of centrifugal pump should be closed when starting, and the outlet valve should be opened when starting gear pump to avoid pressure suppression

13. Which occasions are cast iron pipe, water gas pipe and seamless steel pipe applicable to petrochemical production

Answer: Cast iron pipes are used for underground water supply mains, gas pipes and sewage pipes

Water gas pipes are often used in water pipes, heating, gas, compressed air and vacuum pipes with low pressure, and also in steam branch pipes and condensate pipes with low pressure

Seamless steel pipes are widely used in the transportation of materials with high water pressure and temperature

14. What are the main components of commonly used petrochemical pipelines

Answer: The commonly used petrochemical pipeline mainly consists of pipes, pipe fittings and valves

15. What are the types of pipe fittings according to their functions? Give one or two examples respectively

Answer: ⑴ It is used to change the direction of the pipeline: such as elbow

(2) Connecting pipeline branch: such as three-way and four-way

(3) Connect two sections of pipeline: such as pipe clamp and union

(4) Change pipeline branch: such as reducer

(5) Blocking pipeline: such as plug

16. Why should pressure vessels be equipped with safety accessories

Answer: In order to ensure the safe operation of pressure vessels and prevent accidents caused by overpressure, in addition to taking measures to eliminate or reduce various factors that cause overpressure in vessels, safety pressure relief devices must be installed on pressure vessels

17. Explain the application of safety valve

Answer: 1) Vessels that may increase pressure due to chemical reaction or other reasons during production

2) A container containing liquefied gases

3) The pressure source of the container is not equipped with a safety valve or although it is equipped with a safety valve, the allowable working pressure of the container is less than the pressure at the pressure source

4) Pressure vessels with maximum working pressure less than the pressure source

18. What are the basic conditions for correct operation of pressure vessels

Answer: 1) Do not overtemperature, overpressure and overload

2) The speed of pressure increase and pressure decrease shall not be too fast

3) Temperature rise and fall shall be carried out at the specified speed

4) The number of starts and stops shall be controlled according to the regulations, and the pressure and temperature shall not fluctuate significantly

5) Safety facilities shall be complete, sensitive and reliable

6) Patrol inspection of fixed point, fixed time and fixed line. 7) If the container is abnormal, take correct measures immediately

19. Why should the outlet valve of the centrifugal pump be closed and cannot be closed for too long

Answer: Close the outlet valve and temporarily make the outlet flow zero. At this time, the power required by the pump is minimum, which can limit the motor load to the lowest level, so as to prevent the motor from burning out due to excessive starting current. After the motor operates normally, the outlet valve should be opened gradually, otherwise the pump casing temperature will rise and the parts will be damaged

20. What are the hazards of cavitation

Answer: When cavitation occurs, the pump will produce noise and vibration, and its head, flow and efficiency will decline. Cavitation accelerates the material damage and shortens the service life of the pump. Serious cavitation will damage the normal operation of the pump and threaten the safety production

21. Why can't the compression ratio of reciprocating compressor be too large

Answer: The temperature of the gas will rise during the compression process, so it needs to be cooled while the gas is compressed, otherwise it will consume power and destroy the lubricating effect of the lubricating oil, and even cause the lubricating oil to catch fire. Water jacket is generally used for cylinder and gas cooling. When the compression ratio is too large (such as more than 6), this method alone cannot work, so the compression ratio cannot be too large

22. What are the reasons for the operation of the pressure vessel or the expansion of the original internal defects during its use

Answer: medium corrosion, scouring and abrasion of high-speed air flow, pressure fluctuation, temperature fluctuation, long-term pressure, etc

23. What are the common damage forms of pressure vessels

Answer: plastic damage, brittle damage, fatigue damage, creep damage, corrosion damage, etc

24. Why do some centrifugal pumps set the minimum flow

Answer: Centrifugal pumps realize liquid transmission by applying kinetic energy to the liquid. When a high-power centrifugal pump operates with the outlet valve closed, the fluid will become hotter and hotter due to the increase of kinetic energy, and in serious cases, the bearing will be burned and cavitation will occur. The minimum flow of some pumps is hot standby for the pump

25. Why do some standby pumps need hot standby? How many hot standby modes are there

Answer: When the medium temperature exceeds 150 ℃, the standby pump should be hot standby. The main purpose is to prevent sudden change of fluid temperature and thermal stress of pump body. There are two general hot standby methods:

1) The hot medium is poured from the outlet of the running pump to the outlet of the standby pump to the inlet, and a small amount of backflow in the pump body

2) Jacket steam heating

26. Function of valve:

A: Valves are components used to control the flow and pressure of fluid in the pipeline. Operators can control and adjust the production process by operating various valves

(1) Opening and closing function&mdash& mdash; Cut off or communicate the flow of fluid in the pipe

(2) Regulation&mdash& mdash; Regulate the flow of fluid in the pipe

(3) Throttling effect&mdash& mdash; Adjust the valve opening, change the pressure drop, and achieve the function of regulating the pressure

27. Stop valve

Answer: The stop valve consists of valve core