Centrifugal pumps are widely used in petrochemical, coal chemical and other chemical industries to transport liquids of different natures, providing the pressure and flow required for chemical reactions. There are many types of centrifugal pumps, which can be divided into acid pumps, alkali pumps, clean water pumps, mud pumps, etc. depending on the nature of the transport medium. The working temperature and working pressure of the conveying medium are different. Therefore, effectively extending the service life of the centrifugal pump and reducing the amount of maintenance have a great effect on improving the economic efficiency of the factory.
1. Selection and installation of centrifugal pump The centrifugal pump should be selected according to the liquid to be transported, and the required performance should be checked. The suction and discharge conditions are analyzed, whether it is intermittent operation or continuous operation. Centrifugal pumps should normally be operated at or near the pressure and flow conditions specified by the manufacturer. The following review should be performed when installing the pump:
1 The basic dimensions, position and elevation should meet the design requirements. The anchor bolts must be properly and correctly fixed in the concrete foundation. The machine should not have missing parts, damage or rust;
2 According to the characteristics of the medium to be transported by the pump, the material of the main parts, shaft seals and gaskets should be checked if necessary;
3 The leveling of the pump shall be in accordance with the provisions of the technical documents of the equipment. If there is no regulation, it shall comply with the provisions of the current national standard “General Specification for Construction and Acceptance of Mechanical Equipment Installation Engineeringâ€;
4 All pipes connected to the pump body, installation of pipe fittings and cleaning requirements of lubricating oil pipes shall comply with the relevant national standards.
2. The trial operation of the pump using the centrifugal pump should meet the following requirements:
1 The steering of the drive should be the same as the steering of the pump;
2 Identify the steering of the pipeline pump and the coaxial pump;
3 The fixed joints should be free from looseness. The specifications and quantity of lubricants for each lubrication part should meet the requirements of the equipment technical documents;
4 The parts with pre-lubrication requirements shall be pre-lubricated as required;
5 All indicating instruments and safety protection devices should be sensitive, accurate and reliable;
6-disc should be flexible and free of abnormalities;
7 The high temperature pump should be preheated before the test run, the temperature should rise evenly, the temperature rise per hour should not exceed 500 °C; the temperature difference between the surface of the pump body and the process pipe with the working medium inlet should not exceed 4090;
8 Set the connection device to eliminate the influence of temperature rise, and set the bypass connection device to provide cooling water source.
Pay attention to the following points when operating the centrifugal pump:
1 It is forbidden to run without water, do not adjust the population to reduce the displacement, and prohibit running under too low flow rate;
2 Monitor the operation process, completely prevent the stuffing box from leaking, and use new packing when replacing the stuffing box;
3 to ensure that the mechanical seal has a fully flushed water flow, water-cooled bearings are prohibited from using excessive water flow;
4 Do not use too much lubricant;
5 Check according to the recommended cycle. Establish operational records including hours of operation, adjustment and replacement of packing, addition of lubricants and other maintenance measures and time. Pumping and discharge pressures, flow rates, input power, wash and bearing temperatures, and vibration conditions should be measured periodically.
3. Maintenance of centrifugal pump 3.1 Analysis of mechanical seal failure of centrifugal pump Centrifugal pump shutdown is mainly caused by the failure of mechanical seal. The performance of failure is mostly leakage, and the reasons for leakage are as follows:
1 Leakage of the static sealing surface of the static ring, the main reasons are: the flatness of the end face, the roughness does not meet the requirements, or the surface is scratched; there are particulate matter between the end faces, causing the two end faces not to operate in the same way; the installation is not in place, the way is not correct.
2 compensation ring seal leakage, the main reasons are: gland deformation, pre-tightening force is uneven; installation is not correct; the quality of the seal ring does not meet the standard; the seal ring selection is wrong.
The actual use effect shows that the part of the sealing element that is ineffective is the moving, the end face of the static ring, the centrifugal pump is sealed, and the crack on the end face of the static ring is a common failure phenomenon. The main reasons are:
1 When the sealing surface is too large, the flushing fluid can't take away the heat generated by the friction pair; the flushing liquid leaks away from the gap of the sealing surface, causing the end surface to overheat and be damaged.
2 The liquid medium vaporizes and expands, so that the two end faces are separated by the vaporization expansion force. When the two sealing faces are pressed together, the lubricating film is broken and the surface of the end face is overheated.
3 The liquid medium has poor lubricity, and the operating pressure is overloaded, and the tracking surfaces of the two sealing surfaces are not synchronized. For example, the high speed pump speed is 20445r/min, the sealing surface center diameter is 7cm, and the line speed is up to 75m/s after the pump is running. When there is a sealing surface lag, the rotation cannot be tracked, and the sealing surface is damaged by the instantaneous high temperature.
4 The seal flushing liquid orifice plate or filter is clogged, resulting in insufficient water and invalidation of the machine seal.
In addition, the sealing surface surface of the sliding groove, the gap when the end surface is attached, the sealing element fails, the main reasons are:
1 The liquid medium is not clean, and there are tiny hard particles, which slide the sealing surface at a high speed and scratch the surface of the end surface and fail.
The pumping parts of the 2 pump are poor in coaxiality. After the pump is turned on, the end face is shaken once every revolution, and the running track of the moving ring is not concentric, causing the end face to vaporize and overheat and wear.
3 The frequent occurrence of hydraulic characteristics of the liquid medium causes the pump unit to vibrate, causing the sealing surface to be misaligned and fail.
The liquid medium corrodes the sealing element, stress concentration, soft and hard material coordination, erosion, auxiliary sealing 0-ring, V-ring, concave ring is incompatible with liquid medium, deformation, etc. will cause mechanical seal surface damage failure, so The damage form should be comprehensively analyzed to find out the root cause and ensure that the mechanical seal runs for a long time.
3.2. Requirements after the centrifugal pump stops running 1 After the centrifugal pump stops running, the pump's population valve should be closed. After the pump is cooled, the valve of the auxiliary system is closed.
2 High-temperature pump parking should be carried out according to the provisions of the equipment technical documents. After parking, it should be half-turned every 20 to 30 minutes until the pump temperature drops to 50 °C.
3 When the cryopump is parked, when there is no special requirement, the pump should always be filled with liquid; the suction valve and the discharge valve should be kept normally open; the cryopump with double mechanical seal, the liquid level controller and the sealing liquid in the pump seal chamber The pumping pressure of the pump should be maintained.
4 Pumps that are easy to crystallize, easy to solidify, and easy to precipitate, should be blocked after stopping the pump, and flush the pump and pipeline with water or other medium in time. 5 Discharge the liquid accumulated in the pump to prevent rust and cracking.
3.3. Storage of centrifugal pump 1 The pump that has not been installed should be coated with a suitable rust inhibitor on the unpainted surface. The oil-lubricated bearing should be filled with the appropriate oil. The grease-lubricated bearing should only be filled. A grease, do not use mixed grease.
2 pumping clean liquid, flushing, suction line, discharge line, pump casing and impeller for a short time, and draining the pump casing, the suction line and the flushing liquid in the discharge line.
3 rows of net bearing housing oil, add clean oil, thoroughly clean the grease and refill with new grease.
4 Seal the suction and discharge ports, store the pump in a clean, dry place, protect the motor windings from moisture, and spray the inside of the pump casing with anti-rust liquid and anti-corrosion liquid.
5 The pump shaft rotates once a month to avoid freezing and lubricate the bearings.
1. Selection and installation of centrifugal pump The centrifugal pump should be selected according to the liquid to be transported, and the required performance should be checked. The suction and discharge conditions are analyzed, whether it is intermittent operation or continuous operation. Centrifugal pumps should normally be operated at or near the pressure and flow conditions specified by the manufacturer. The following review should be performed when installing the pump:
1 The basic dimensions, position and elevation should meet the design requirements. The anchor bolts must be properly and correctly fixed in the concrete foundation. The machine should not have missing parts, damage or rust;
2 According to the characteristics of the medium to be transported by the pump, the material of the main parts, shaft seals and gaskets should be checked if necessary;
3 The leveling of the pump shall be in accordance with the provisions of the technical documents of the equipment. If there is no regulation, it shall comply with the provisions of the current national standard “General Specification for Construction and Acceptance of Mechanical Equipment Installation Engineeringâ€;
4 All pipes connected to the pump body, installation of pipe fittings and cleaning requirements of lubricating oil pipes shall comply with the relevant national standards.
2. The trial operation of the pump using the centrifugal pump should meet the following requirements:
1 The steering of the drive should be the same as the steering of the pump;
2 Identify the steering of the pipeline pump and the coaxial pump;
3 The fixed joints should be free from looseness. The specifications and quantity of lubricants for each lubrication part should meet the requirements of the equipment technical documents;
4 The parts with pre-lubrication requirements shall be pre-lubricated as required;
5 All indicating instruments and safety protection devices should be sensitive, accurate and reliable;
6-disc should be flexible and free of abnormalities;
7 The high temperature pump should be preheated before the test run, the temperature should rise evenly, the temperature rise per hour should not exceed 500 °C; the temperature difference between the surface of the pump body and the process pipe with the working medium inlet should not exceed 4090;
8 Set the connection device to eliminate the influence of temperature rise, and set the bypass connection device to provide cooling water source.
Pay attention to the following points when operating the centrifugal pump:
1 It is forbidden to run without water, do not adjust the population to reduce the displacement, and prohibit running under too low flow rate;
2 Monitor the operation process, completely prevent the stuffing box from leaking, and use new packing when replacing the stuffing box;
3 to ensure that the mechanical seal has a fully flushed water flow, water-cooled bearings are prohibited from using excessive water flow;
4 Do not use too much lubricant;
5 Check according to the recommended cycle. Establish operational records including hours of operation, adjustment and replacement of packing, addition of lubricants and other maintenance measures and time. Pumping and discharge pressures, flow rates, input power, wash and bearing temperatures, and vibration conditions should be measured periodically.
3. Maintenance of centrifugal pump 3.1 Analysis of mechanical seal failure of centrifugal pump Centrifugal pump shutdown is mainly caused by the failure of mechanical seal. The performance of failure is mostly leakage, and the reasons for leakage are as follows:
1 Leakage of the static sealing surface of the static ring, the main reasons are: the flatness of the end face, the roughness does not meet the requirements, or the surface is scratched; there are particulate matter between the end faces, causing the two end faces not to operate in the same way; the installation is not in place, the way is not correct.
2 compensation ring seal leakage, the main reasons are: gland deformation, pre-tightening force is uneven; installation is not correct; the quality of the seal ring does not meet the standard; the seal ring selection is wrong.
The actual use effect shows that the part of the sealing element that is ineffective is the moving, the end face of the static ring, the centrifugal pump is sealed, and the crack on the end face of the static ring is a common failure phenomenon. The main reasons are:
1 When the sealing surface is too large, the flushing fluid can't take away the heat generated by the friction pair; the flushing liquid leaks away from the gap of the sealing surface, causing the end surface to overheat and be damaged.
2 The liquid medium vaporizes and expands, so that the two end faces are separated by the vaporization expansion force. When the two sealing faces are pressed together, the lubricating film is broken and the surface of the end face is overheated.
3 The liquid medium has poor lubricity, and the operating pressure is overloaded, and the tracking surfaces of the two sealing surfaces are not synchronized. For example, the high speed pump speed is 20445r/min, the sealing surface center diameter is 7cm, and the line speed is up to 75m/s after the pump is running. When there is a sealing surface lag, the rotation cannot be tracked, and the sealing surface is damaged by the instantaneous high temperature.
4 The seal flushing liquid orifice plate or filter is clogged, resulting in insufficient water and invalidation of the machine seal.
In addition, the sealing surface surface of the sliding groove, the gap when the end surface is attached, the sealing element fails, the main reasons are:
1 The liquid medium is not clean, and there are tiny hard particles, which slide the sealing surface at a high speed and scratch the surface of the end surface and fail.
The pumping parts of the 2 pump are poor in coaxiality. After the pump is turned on, the end face is shaken once every revolution, and the running track of the moving ring is not concentric, causing the end face to vaporize and overheat and wear.
3 The frequent occurrence of hydraulic characteristics of the liquid medium causes the pump unit to vibrate, causing the sealing surface to be misaligned and fail.
The liquid medium corrodes the sealing element, stress concentration, soft and hard material coordination, erosion, auxiliary sealing 0-ring, V-ring, concave ring is incompatible with liquid medium, deformation, etc. will cause mechanical seal surface damage failure, so The damage form should be comprehensively analyzed to find out the root cause and ensure that the mechanical seal runs for a long time.
3.2. Requirements after the centrifugal pump stops running 1 After the centrifugal pump stops running, the pump's population valve should be closed. After the pump is cooled, the valve of the auxiliary system is closed.
2 High-temperature pump parking should be carried out according to the provisions of the equipment technical documents. After parking, it should be half-turned every 20 to 30 minutes until the pump temperature drops to 50 °C.
3 When the cryopump is parked, when there is no special requirement, the pump should always be filled with liquid; the suction valve and the discharge valve should be kept normally open; the cryopump with double mechanical seal, the liquid level controller and the sealing liquid in the pump seal chamber The pumping pressure of the pump should be maintained.
4 Pumps that are easy to crystallize, easy to solidify, and easy to precipitate, should be blocked after stopping the pump, and flush the pump and pipeline with water or other medium in time. 5 Discharge the liquid accumulated in the pump to prevent rust and cracking.
3.3. Storage of centrifugal pump 1 The pump that has not been installed should be coated with a suitable rust inhibitor on the unpainted surface. The oil-lubricated bearing should be filled with the appropriate oil. The grease-lubricated bearing should only be filled. A grease, do not use mixed grease.
2 pumping clean liquid, flushing, suction line, discharge line, pump casing and impeller for a short time, and draining the pump casing, the suction line and the flushing liquid in the discharge line.
3 rows of net bearing housing oil, add clean oil, thoroughly clean the grease and refill with new grease.
4 Seal the suction and discharge ports, store the pump in a clean, dry place, protect the motor windings from moisture, and spray the inside of the pump casing with anti-rust liquid and anti-corrosion liquid.
5 The pump shaft rotates once a month to avoid freezing and lubricate the bearings.
Xi'an Jmlai Bio-Tech Co., Ltd. , https://www.jmlaisarms.com