1. Selection and installation of centrifugal pump

Centrifugal pump should be selected according to the liquid delivered, and check the required performance, analyze the suction and discharge conditions, whether intermittent or continuous operation, etc. The centrifugal pump shall normally operate at or close to the pressure and flow conditions specified by the manufacturer. The following rechecks shall be carried out during pump installation:

① The size, position and elevation of the foundation shall meet the design requirements. The anchor bolts must be properly and correctly fixed in the concrete foundation. The machine shall not be missing, damaged or corroded;

② According to the characteristics of the medium delivered by the pump, the material of main parts, shaft seals and gaskets should be checked when necessary;

③ The leveling and alignment of the pump shall comply 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 code for construction and acceptance of mechanical equipment installation engineering";

④ All pipes connected with pump body, installation of pipe fittings and cleaning requirements of lubricating oil pipeline shall comply with relevant national standards.

2. Use of centrifugal pump

The test run of the pump shall meet the following requirements:

① The steering of the driving machine should be the same as that of the pump;

② Find out the steering direction of pipeline pump and coaxial pump;

③ Each fixed connection part shall be free from looseness, and the specification and quantity of lubricant applied to each lubricating part shall comply with the provisions of technical documents of the equipment;

④ Parts with pre lubrication requirements shall be pre lubricated according to regulations;

⑤ All indicating instruments and safety protection devices shall be sensitive, accurate and reliable;

⑥ The turning gear shall be flexible without abnormal phenomenon;

⑦ Before the commissioning of high temperature pump, the pump body should be preheated, the temperature should rise evenly, and the temperature rise per hour should not be greater than 500 ℃; the temperature difference between the pump surface and the process pipeline with working medium inlet should not be greater than 4090;

⑧ The connection device to eliminate the influence of temperature rise is set, and the bypass connection device is set to provide cooling water source.

Centrifugal pump operation should pay attention to the following points:

① It is forbidden to operate without water, do not adjust the suction population to reduce the displacement, and it is forbidden to operate under low flow rate;

② Monitor the operation process, completely prevent the leakage of the stuffing box, and use new packing when replacing the stuffing box;

③ Ensure that the mechanical seal has sufficient water flow for flushing, and excessive water flow is prohibited for water-cooled bearings;

④ Do not use too much lubricant;

⑤ Check according to the recommended period. Establish operation records, including operating hours, packing adjustment and replacement, lubricant addition and other maintenance measures and time. The suction and discharge pressure, flow rate, input power, temperature of washing liquid and bearing and vibration of centrifugal pump should be measured and recorded regularly.

3. Maintenance of centrifugal pump

3.1 failure analysis of centrifugal pump mechanical seal

The shutdown of centrifugal pump is mainly caused by the failure of mechanical seal. The performance of failure is mostly leakage, and the leakage causes are as follows:

① The main reasons for the leakage of dynamic and static ring sealing surfaces are: the flatness and roughness of the end face do not meet the requirements, or there are scratches on the surface; there are particles between the end faces, resulting in the two ends can not run the same way; the installation is not in place, and the way is not correct.

② The main reasons for the leakage of compensation ring seal ring are: gland deformation, uneven pre tightening force, incorrect installation, unqualified sealing ring quality and incorrect selection of sealing ring.

The practical application results show that the most failure parts of the sealing elements are the end faces of the dynamic and static rings. The cracking of the end faces of the static rings is a common failure phenomenon when the centrifugal pumps are sealed

① During installation, the clearance between the sealing faces is too large, and the flushing fluid has no time to take away the heat generated by the friction pair; the flushing fluid leaks out from the seal face gap, causing the end face to be overheated and 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 surfaces are forced to fit together, the lubricating film will be destroyed and the end surface will be overheated.

③ Due to poor lubricity of liquid medium and overload of operating pressure, the tracking rotation of two sealing faces is not synchronous. For example, the rotating speed of high-speed pump is 20445r / min, and the center diameter of sealing surface is 7cm. After the pump is running, its linear speed is as high as 75 m / s. when one sealing surface lags behind and cannot track the rotation, the instantaneous high temperature will damage the sealing surface.

④ Sealing flushing fluid orifice plate or filter screen is blocked, resulting in insufficient water and mechanical seal failure.

In addition, the sliding groove on the surface of the sealing surface and the gap during the end face fitting lead to the failure of the sealing element

① The liquid medium is not clean, there are tiny hard particles, which slide into the sealing surface at a high speed, scratch the surface of the end face and lose efficacy.

② The coaxiality of the transmission parts of the pump is poor. After the pump is started, the end face is shaken and rubbed once every revolution. The moving ring running track is not concentric, resulting in vaporization of the end face, overheating and wear.

③ The frequent occurrence of hydraulic characteristics of liquid medium causes the vibration of pump set, resulting in dislocation of sealing surface and failure.

The corrosion of liquid medium to sealing elements, stress concentration, matching of soft and hard materials, erosion, auxiliary seal 0-ring, V-ring, concave ring and liquid medium incompatibility, deformation and so on, will cause mechanical seal surface damage and failure, so the damage form should be comprehensively analyzed to find out the root cause to ensure the long-term operation of mechanical seal.

3.2 requirements after the centrifugal pump stops running

① After the centrifugal pump stops running, close the population valve of the pump, and then close the valve of the auxiliary system successively after the pump cools down.

② The shutdown of the high temperature pump shall be carried out according to the provisions of the technical documents of the equipment. After the shutdown, the turning gear shall be turned for half a circle every 20-30 minutes until the temperature of the pump body drops to 50 ℃.

③ When the cryogenic pump is shut down, when there is no special requirement, the pump