Centrifugal pumps are widely used in petrochemical, coal chemical and other chemical industries, the transmission of different nature of the liquid to provide the chemical reaction pressure, flow. Centrifugal pump of a wide range, according to the nature of the transmission medium can be divided into acid pump, alkali pump, water pump, mud pump. Transmission medium temperature and working pressure of different, therefore, effectively extend the life cycle of centrifugal pumps and reduce the amount of maintenance, to improve the economic efficiency of the plant has a significant role.
1, centrifugal pump selection and installation
Centrifugal pumps should be selected according to the liquid being conveyed and to check the required performance, analyze the suction, discharge conditions, intermittent operation or continuous operation. Centrifugal pumps should normally be operated at or near the pressure and flow rates specified by the manufacturer's design. The pump should be installed for the following review:
â‘ The basic size, location and elevation should meet the design requirements. The anchor bolts must be properly and correctly fixed on the concrete foundation. The machine should not be missing, damaged or corroded.
â‘¡ According to the characteristics of the pump transmission medium, if necessary, check the main parts, shaft seals and gasket material;
â‘¢ Pump leveling, find work should be consistent with the provisions of technical documents, if there is no provision, should be consistent with the existing national standards, "Machinery and Equipment Installation Engineering Construction and Acceptance of Common Specifications" requirement;
â‘£ All connected with the pump pipe, pipe fittings and oil pipe cleaning requirements should be consistent with the relevant national standards.
2, the use of centrifugal pumps
Pump running test should meet the following requirements:
â‘ drive the steering should be the same with the pump steering;
â‘¡ identify the pipeline pump and coaxial pump steering;
 '¢ the fixed connection should be no loose parts, the lubricating parts filling lubricant specifications and quantity should be consistent with the provisions of technical documents;
â‘£ pre-lubrication requirements of the site should be pre-lubricated;
⑤ all indicating instruments, safety devices should be sensitive, accurate and reliable;
â‘¥ crank should be flexible, no abnormalities;
⑦ high temperature pump should be carried out before commissioning pump body preheating, the temperature should rise evenly, the temperature rise per hour should not exceed 500 ℃; pump the surface of the working medium with a working medium inlet temperature difference should not exceed 4090;
⑧ set to eliminate the impact of temperature rise of the connection device, set the bypass connection device to provide cooling water.
Centrifugal pump operation should note the following:
â‘ prohibit anhydrous operation, do not adjust the suction port to reduce emissions, prohibit the operation of low flow;
â‘¡ monitor the operation of the process, completely prevent packing box leakage, replace the packing box with a new filler;
â‘¢ to ensure that mechanical seals have a full flush of water, water-cooled bearings prohibit the use of excessive water flow;
â‘£ lubricant do not use too much;
⑤ according to the recommended cycle of inspection. Establish operating records including operating hours, packing adjustments and replacements, adding lubricants and other maintenance measures and times. Centrifugal pump suction and discharge pressure, flow, power input, lotion and bearing temperature and vibration conditions should be measured regularly recorded.
3, centrifugal pump maintenance
3.1, centrifugal pump mechanical seal failure analysis
Centrifugal pump downtime is mainly caused by the failure of the mechanical seal. The failure of the performance of most of the leaks, leaks for the following reasons:
â‘ static and dynamic ring seal surface leakage, mainly due to: face flatness, roughness does not meet the requirements, or scratches the surface; between the end of the particulate matter, resulting in both ends can not be the same run; installation is not in place, the way is not correct.
â‘¡ compensation ring seal leakage, mainly due to: gland deformation, uneven pre-tightening; installation is not correct; seal quality does not meet the standards; seal selection wrong.
The actual use of the results show that the seal failure of the most parts of the dynamic and static end of the ring, the centrifugal pump seal, static ring end face cracking is a common failure phenomenon, the main reasons are:
â‘ installation seal surface clearance is too large, too late to take away the flushing liquid generated by friction heat; flushing fluid leak from the gap in the sealing surface, resulting in overheating and damage to the end.
â‘¡ vaporization of liquid medium expansion, so that the two ends by the expansion of vaporization and separation, when the two sealing surface force fit, the destruction of the lubricating film resulting in the end surface overheating.
â‘¢ liquid medium lubrication is poor, combined with the operating pressure overload, two sealing surface tracking rotation is not synchronized. For example, high-speed pump speed of 20445r / min, the center of the sealing surface diameter of 7cm, pump speed after the line up to 75m / s, when there is a sealing surface can not track the hysteresis rotation, instantaneous sealing surface damage caused by high temperature.
â‘£ seal flushing fluid orifice or filter blockage, resulting in insufficient water, so that machine seal failure.
In addition, the sealing surface of the surface of the sliding groove, the end face of the gap caused by seal failure, mainly due to:
â‘ liquid medium is not clean, there are tiny hard particles, with a very high speed sliding sealing surface, the end surface scratches and failure.
â‘¡ poor coaxial pump drive parts, the pump is turned on each revolution after a week was shaking the friction end, moving the ring trajectory is not the same heart, resulting in end vaporization, overheating wear.
â‘¢ frequent occurrence of hydraulic properties of liquid medium caused pump vibration, resulting in seal surface dislocation and failure.
Liquid medium on the sealing element corrosion, stress concentration, with hard and soft materials, erosion, auxiliary seal 0-ring, V-ring, concave ring and the liquid medium is not compatible, deformation and so will cause mechanical seal surface damage failure, so Damage to the form of a comprehensive analysis to identify the root causes, to ensure long-term mechanical seal operation.
3.2, centrifugal pump stop running after the request
â‘ Centrifugal pump should be shut down after stopping the pump population valve, to be cooled and then turn off the auxiliary system valves.
② high-temperature pump should be stopped according to the provisions of technical documents, after parking should be partial 20 -30 30min half a turn until the pump temperature dropped to 50 ℃ so far.
â‘¢ cryogenic pump parking, when no special requirements, the pump should always be filled with liquid; suction valve and the discharge valve should be kept normally open state; the use of double-end mechanical seal of the cryogenic pump, liquid level controller and seal the liquid seal chamber The pump grouting pressure should be maintained.
④ transport easy to crystallize, easy to coagulate, easy precipitation and other media pump, stop the pump should be blocked, and timely flush with water or other media pumps and pipes. ⑤ discharge liquid stored in the pump to prevent corrosion and cracking.
3.3, centrifugal pump custody
â‘ not yet installed on the unpainted pump surface should be coated with a suitable rust inhibitor, lubricated bearings should be filled with the appropriate oil, grease-lubricated bearings should be filled with only a grease, do not Use mixed grease.
â‘¡ a short time pump clean liquid, flushing, suction lines, discharge lines, pump housing and impeller, side by side net pump housing, suction lines and discharge lines in the flushing fluid.
â‘¢ drain the oil bearing box, then add clean oil, thoroughly clean the grease and then fill the new grease.
â‘£ The suction port and exhaust port sealed up, the pump stored in a clean, dry place, to protect the motor windings from damp, with anti-rust liquid and anti-cavitation spray pump housing inside.
⑤ pump shaft rotation once a month to avoid freezing, and lubrication of bearings.
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