A good way to prolong the service cycle of centrifugal pump

Centrifugal pumps are widely used in petrochemical, coal chemical and other chemical industries to transport liquids of different properties and provide 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. according to the nature of the conveying medium. The working temperature and working pressure of the conveying medium are different. Therefore, it is effective to extend the service life of the centrifugal pump and reduce the maintenance amount, which has a great effect on improving the economic efficiency of the factory.

1. Centrifugal pump selection and installation

The centrifugal pump should be selected according to the liquid to be transported, and the required performance should be checked, and the suction and discharge conditions should be analyzed, whether it is intermittent operation or continuous operation, etc. Centrifugal pumps should usually be operated at or close to the pressure and flow conditions specified by the manufacturer. The following rechecks should be made during pump installation:

• ①The size, location and elevation of the foundation should meet the design requirements, the anchor bolts must be properly and correctly fixed in the concrete foundation, and the machine should not be missing, damaged or rusted;
• ②According to The characteristics of the medium conveyed by the pump should be checked if necessary, the materials of the main parts, shaft seals and gaskets;
• ③The leveling and alignment of the pump should comply with the requirements of the equipment technical documents, and if there are no regulations, it should comply with the current national standards. The requirements of the General Specification for Construction and Acceptance of Mechanical Equipment Installation Engineering;
• ④All the pipes connected to the pump body, the installation of pipe fittings and the cleaning requirements of the lubricating oil pipes shall comply with the relevant national standards.

2, the use of centrifugal

pumps commissioning shall meet the following requirements:

• ① same steering driver should turn the pump;
• ② pumps and coaxial pipelines to identify a steering pump;
• ③ respective fixed should be no loose joints, lubrication The specification and quantity of lubricants added to the parts should meet the requirements of the equipment technical documents;
• ④The parts with pre-lubrication requirements should be pre-lubricated according to the regulations;
• ⑤All indicating instruments and safety protection devices should be sensitive, accurate and reliable;
• ⑥Cranking Should be flexible, no abnormal phenomena;
• ⑦The high temperature pump should be preheated before trial operation, the temperature should rise uniformly, and the hourly temperature rise should not be greater than 500℃; the temperature difference between the surface of the pump body and the process pipeline with the working medium inlet should not be greater than 4090;
• ⑧Set to eliminate For connecting devices affected by temperature rise, a bypass connecting device is provided to provide a source of cooling water.

Pay attention to the following points when operating the centrifugal pump:

• ①It is forbidden to run without water, do not adjust the suction to reduce the displacement, and it is forbidden to run under too low flow;
• ②Monitor the operation process to completely prevent the stuffing box from leaking, and when replacing the stuffing box Use new packing;
• ③Ensure that the mechanical seal has sufficient flushing water flow, and excessive water flow is prohibited for water-cooled bearings;
• ④Do not use too much lubricant;
• ⑤Check according to the recommended cycle. Establish operating records, including operating hours, adjustment and replacement of fillers, adding lubricants and other maintenance measures and time. The centrifugal pump suction and discharge pressure, flow rate, input power, temperature of washing liquid and bearing, and vibration should be measured and recorded regularly.

3. Maintenance of the centrifugal pump

3.1 Analysis of the failure of the mechanical seal of the centrifugal pump The downtime of the centrifugal pump is mainly caused by the failure of the mechanical seal. Most of the failure manifestations are leakage, and the reasons for leakage are as follows:

• ①Leakage of the sealing surface of the dynamic and static ring, the main reasons are: the flatness of the end surface, the roughness does not meet the requirements, or the surface is scratched; there is particulate matter between the end surfaces, causing two The end face cannot be operated in the same way; the installation is not in place and the way is incorrect.
• ② The sealing ring of the compensation ring leaks. The main reasons are: the gland is deformed and the pre-tightening force is uneven; the installation is not correct; the quality of the sealing ring does not meet the standard; the type of the sealing ring is incorrect.

The actual use results show that the most failure of the sealing element is the end face of the dynamic and static ring, the centrifugal pump machine seals the dynamic, the end face of the static ring is a common failure phenomenon, the main reasons are:

• ①The sealing surface gap is too large during installation. The flushing fluid is too late to take away the heat generated by the friction pair; the flushing fluid leaks from the gap of the sealing surface, causing the end surface to overheat and damage.
• ② The liquid medium vaporizes and expands, so that the two ends are separated by the vaporization and expansion force. When the two sealing surfaces are firmly attached, the lubricating film is destroyed and the end surface is overheated.
• ③The liquid medium has poor lubricity, and the operating pressure is overloaded, and the tracking and rotation of the two sealing surfaces are not synchronized. For example, the high-speed pump speed is 20445r/min, the center diameter of the sealing surface is 7cm, and the linear speed of the pump is as high as 75 m/s after the pump is running. When a sealing surface lags behind and cannot track the rotation, the instantaneous high temperature causes the sealing surface to be damaged.
• ④ The orifice plate or filter screen of the sealing flushing fluid is blocked, resulting in insufficient water volume and failure of the mechanical seal.

In addition, slip grooves on the surface of the sealing surface and gaps in the end surface will cause the sealing element to fail. The main reasons are:

• ①The liquid medium is not clean, and there are tiny hard particles. Injury and fail.
• ②The coaxiality of the transmission parts of the machine and pump is poor. After the pump is turned on, the end face is swayed and rubbed once per revolution, and the moving trajectory of the moving ring is not concentric, causing the end face to vaporize, overheating and abrasion.
• 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 corrosion of the sealing element by the liquid medium, stress concentration, soft and hard material coordination, erosion, auxiliary seal 0-ring, V-ring, concave ring and liquid medium incompatibility, deformation, etc. will cause damage and failure of the mechanical seal surface, so The damage form must be analyzed comprehensively to find the root cause to ensure the long-term operation of the mechanical seal.

3.2 Requirements after the centrifugal pump stops running

• ① After the centrifugal pump stops running, the inlet valve of the pump should be closed, and the valves of the auxiliary system should be closed in turn after the pump has cooled down.
• ②The shutdown of the high-temperature pump should be carried out in accordance with the provisions of the equipment technical documents. After parking, the car should be cranked every 20 to 30 minutes until the temperature of the pump body drops to 50°C.
• ③When the cryopump is stopped, 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 seals, the liquid level controller and the sealing liquid in the pump seal cavity The grout pressure of the pump should be maintained.
• ④ Pumps that transport media that are easy to crystallize, solidify, and precipitate, etc., should be prevented from being blocked after the pump is stopped, and the pump and pipeline should be flushed with water or other media in time. ⑤Drain the liquid accumulated in the pump to prevent rust and frost cracking.

3.3. Storage of the centrifugal pump

• ① The un-installed pump should be coated with a suitable anti-rust agent on the unpainted surface, the bearing lubricated with oil should be filled with proper oil, and the bearing lubricated with grease should only be filled A kind of grease, do not use mixed grease.
• ②Pump clean liquid for a short time, flush, suction pipeline, discharge pipeline, pump casing and impeller, and drain the flushing liquid in pump casing, suction pipeline and discharge pipeline side by side.
• ③Drain the oil in the bearing box, add clean oil, thoroughly clean the grease and then fill with new grease.
• ④ Seal the suction port and discharge port, 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 and anti-corrosion liquid.