Repair of pumping equipment
Reliable and trouble-free operation of pumping equipment is ensured only through proper supervision and timely repair.
The current repair of horizontal centrifugal pumps includes: changing gaskets, stuffing glands, changing sealing rings, eliminating the run-up of the rotor, changing bearings, centering the pump, oil painting of the pump unit and pipelines. The duration of the period between current repairs is no more than three months or as needed.
Overhaul includes: a complete revision of the pump with disassembly, cleaning, adjustment and replacement of parts; impeller balancing; shaft change; shaft straightening by turning; grinding of shaft necks and sealing rings; replacement of impellers and seals; refilling or changing the bearing shells: cutting or building up the pump impellers. The frequency of work on the overhaul of centrifugal pumps of pumping stations is 1.5 ... 3 years.
Stuffing boxes of horizontal centrifugal pumps are filled with stuffing box packings (GOST 5152-84) of round or square section. The cross-sectional dimensions of the packings are checked with a caliper or thickness gauge. Their appearance is checked visually: the surface of the packings should not have local thickenings, irregularities, damage to the braid, protruding broken threads.
Before use, the HBS stuffing is pre-boiled in technical fat.
The gland packing must be changed to a new one every 300-500 hours of operation, depending on the water temperature, the presence of mechanical impurities, etc.
The Institute of Ukrkommunproekt MZhKH of the Ukrainian SSR developed technical documentation for the reconstruction of stuffing box seals of pumps operating with excess pressure (0.7-4 m) when water is supplied to stuffing box seals from an external source or pump head cavity. The pressure drop, for example, in the pump D 4000-95 (22 VAT) is 0.95 MPa. This leads to increased wear of the stuffing box rings and protective bushings. Friction power losses for pumps of this brand are up to 26 kWh.
The reconstruction of stuffing box seals consists in the fact that the water supply to them is dismantled. Hole B is plugged. The three inner rings of the packing and the hydraulic locking ring are removed, and in their place a manufactured steel bushing and three rings of stuffing box packing are installed, between which fluoroplastic or paronite gaskets 2-3 mm thick are placed.
With proper assembly of the stuffing box seal, the rotor rotates freely on the shaft, and the amount of water leakage is in the range of 5 ... 10 l / h. The economic effect on MZHKH of the Ukrainian SSR amounted to 340 thousand rubles per year.
Rice. 1. Reconstruction of stuffing box seals of pumps of type "D" operating under pressure:
1 - remote bushing (cast iron, steel, bronze, fluoroplast); 2 - cork (steel, cast iron, plastic); 3 - gasket (fluoroplast sheet 6-2 ... 3 mm); 4 - stuffing box; 5 - protective sleeve (cast iron sch20, steel 45 or 20X13 HRC
40…30); 6 - axle box (pressure bushing); 7 - round nut.
The nature of the repair of the pump is determined during its disassembly, and at the same time a fault card is drawn up for the components and parts of the pump.
The pump is disassembled as follows: first, the coupling guard is removed, and then the fingers of the elastic coupling and the gland boxes; disconnect the end caps of the bearings; release the studs along the housing connector, undermine the pump cover with forcing screws and remove it, remove the rotor and lay it on the goats; remove coupling halves, sealing rings, ball bearings and impeller.
When disassembling the components and parts of the pump, the condition of the seating and sealing surfaces is monitored.
The pump is assembled in the reverse order.
Before assembly, the seating surfaces are lubricated with oil.
In horizontal centrifugal pumps, to reduce volume losses, a seal is rigidly installed on the impeller, and a fixed seal is pressed into the pump casing. As the seal on the impeller wears out, replace it with a new one.
In case of wear of babbitt bearings, their liners are refilled, for which B-16 or B-83 babbit is used. The degree of wear of the bearings is determined by measurements between the pump shaft and the bearing shell. For the timely replacement of worn-out rolling bearings that have become unusable, the enterprise must have the necessary reserve of them.
Long-term and trouble-free operation of the pumping unit depends on the quality of the lubrication of the bearings.
In domestic production, liquid and grease lubricants are used. Liquid must be changed every 300-500 hours worked, consistent - after 3-5 months of pump operation.
Preparation for repair of a centrifugal pump.
Pumping equipment, after the expiration of the periods between overhauls determined by the norms, stops for current, medium or major repairs.
Any repair begins with the disassembly of the entire machine or individual components to be repaired. The disassembly is carried out by the repair team of the workshop together with the maintenance personnel of the installation.
Current repairs include:
cleaning and washing
in the middle repair: except for the work performed during the current repair - checking the condition of the foundation, checking the drive
in the capital: a complete disassembly of the machine is required, the foundation, shaft, impeller, attachment to the foundation will be checked, all defective parts will be replaced.
Disturbances in the operation of a centrifugal pump associated with malfunctions of its piping (omissions in flanged connections, clogging of pipes, poor fixing)
too much run-out of the shaft, leading to the end of the impeller touching the casing, is eliminated by adjusting the set nuts, installing thicker seals between the casing and the back cover.
The friction of the wheel groove against the O-ring with a horizontal body split can be eliminated by scraping the ring or by installing adjusting shims.
The cause of many problems is the contamination of the internal parts of the pump with a thickened liquid, corrosion products. Therefore, cleaning and washing parts is one of the main repair operations. As a rule, the parts are washed twice: first, a deep flush, then with clean kerosene, the final one.
Parts should not come into contact with the bottom of the rack (during washing), from which they should be separated with a sheet of plywood or cardboard. For washing, use hair brushes, and for wiping, clean, dense rags, free of fibers and nets. Instead of wiping, you can use compressed air to dry.
If during repair it is necessary to replace a worn unit, it is removed from the box and cleaned of preservative grease. Then the assembly is disassembled, all parts are marked and carefully inspected. Next, the assembly is assembled and installed on the site.
After the repair, the pumping equipment is assembled, its hydraulic test, and running.
The assembly of the repaired pump must be carried out by monitoring compliance with the allowable clearances between rotating and stationary parts. The gap between the sealing ring and the impeller groove (depending on the size of the pump) is in the range of 0.2-0.5 mm. The check is carried out with probes of the appropriate thickness. The gap between the gland bushings and the shaft should be 0.2-1 mm
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A few rules for the operation of centrifugal pumps
Both types of centrifugal equipment require a conscious approach to their operation. Namely, compliance with several important rules that will extend the life of your unit.
The most important thing to remember and strictly observe is that a centrifugal pump should only start if there is water in its chamber. Running dry can damage the pump in the very near future
And if everything is clear with the submersible unit (it is always in the working environment), then the surface mechanism can be saved by pouring water into its working chamber before starting and installing a check valve on the water pipe. For a submersible pump, it is important to have a float switch that will work in the event of a drop in the water level in the source.
In addition, no centrifugal pump likes the presence of impurities in the water in the form of sand, clay or other small debris. Therefore, for a surface device, it is important to have a high-quality mesh filter at the end of the intake pipe. And for a submersible pump, it is important to equip the bottom filter of a well or well with high quality. Or do not install the centrifugal pump in a well/well with a sandy or quicksand bottom. For such sources, it is better to choose a vibration or screw pump.
And don't forget to regularly inspect your pumping equipment. This is especially true of the submersible unit, which needs to be raised and listened to at least twice a year in operating mode for the presence of extraneous noise in the chamber.
It is important to buy and install a centrifugal pump designed for the debit of your particular source. If the performance of the unit is higher than the flow rate of the well / well, then there is a risk of the pump running dry. In this case, special impellers can save the situation, which will regulate the pressure in the outlet chamber for a stable flow of water into the pump itself and into the water supply system.
If you operate the centrifugal pump not constantly, but periodically, then you must turn on the pump at least once a month for 15 minutes to avoid oxidation of all working elements of the pump.
It is also worth paying attention to the volume of water that the centrifugal unit is capable of pumping within its technical specifications. If the recommended and actual power do not match, then there is a risk of damaging the pump. Remember that a unit designed to process 3m3 / h and at the same time transport water in a volume of 2 or 4 m3 / h will wear out its working units.
How to properly operate
In order for malfunctions to begin to occur as late as possible, you should follow the rules for operating the equipment:
- Before turning on the unit, it is necessary to fill its entire working tank with liquid.
- Do not allow the suction pipe, protective meshes and pump impeller to become clogged. For this purpose, a coarse filter is installed in front of the device.
- Avoid overloading the engine by limiting the fluid supply with a special valve that is placed on the outgoing pipe.
- Make sure that the water pump shafts rotate in the correct direction.
- Do not allow the suction lift to exceed the permitted level.
- The suction pipe should have as few inserts and bends as possible, its internal diameter should be as large as possible, and its length as short as possible.
- If the length of the suction pipeline is long, then it should be laid with an inclination towards the place where the liquid is pumped. If it is impossible to provide a slope, the pump is installed at the highest point of the territory.
- In the case of pumping any gas mixtures, the system must also include a vacuum pump.
Repair
Centrifugal pump device. (click to enlarge) A unit such as a centrifugal pump, even in its simplest version, has a rather complex device.
Therefore, its repair will require knowledge, experience and certain skills.
Here are the main steps for repairing pumps:
- disassembly and inspection of the unit;
- measurement of gaps of seals and control of the state of the rotor;
- installation of new bearings to replace the old ones;
- control of the geometry of the shaft journals. In case of detection of their defects, the shaft is machined and polished;
- correction of detected defects;
- hull geometry measurement.
This is a scheduled maintenance that is worth doing every 4,500 hours of use.
But every 26,000 hours of using the unit, it needs a more complex repair, during which the following are carried out:
- replacement of the working shaft and wheel;
- change of body seal rings, bushings, both expansion and clamping;
- sometimes the replacement of sections completely, for sectional units;
- surfacing and boring of landing places in the body;
- hydraulic testing of the unit.
When doing repairs with your own hands, it should be noted that the most difficult thing will be:
- disassemble bearings;
- remove the liners;
- remove the clutch half. To do this, you will need to use a special puller that comes with the pump;
- dismantle the unloading disk of the hydro-heel;
- remove the pressure flange.
When removing the impellers, it is important not to bring them to jamming, the removal is carried out in turn with each section. If there is difficulty with this operation, but the wheel should be slightly warmed up
It is advisable not to remove the guides from the sections.
You may also be interested in an article about the features of installation and testing of centrifugal pumps.
Comparison of vortex and centrifugal pumps is covered in this article.
After identifying all the parts that have become unusable, you can proceed to another difficult task - assembling the pump.
During its implementation, you will have to perform quite delicate work:
- check the compliance of new parts with those that stood before and the drawings available in the instructions;
- adjust spare parts to their installation sites;
- grind and grind the surfaces on which the parts are planted;
- evenly tighten all screw fasteners using a torque wrench, exactly observing the tightening force;
- assemble the impeller with exact observance of the axial clearance, directly on the shaft;
- when installing the unloading disk, observe the perpendicularity of its end side, avoiding an error of more than 0.02 mm.
It should be noted that, if the impeller or casing is destroyed, they should not be welded, since this is unreliable and this is not done even in the factory.
Most often at home they perform such work:
- check and change bearings;
- wash and clean the crankcase;
- change the lubricant;
- check the condition of the seals;
- wash the oil lines;
- check the centering of the unit.
Sometimes repairing the pump can cost such a significant amount that it will be easier to purchase a new one.
Watch the video in which an experienced user shows in detail the steps for repairing a centrifugal water pump with his own hands:
Common breakdowns
If no external factors have a harmful effect on the pump, and it does not work correctly, or does not work at all, you should proceed to a thorough check of it.
Most often, the problems are caused by wear of the seals.
There are a number of reasons that speed up this process:
- Uneven movement of the shaft, especially with frequent beating.
- Unit cover bolts too tight. The stuffing boxes do their best job of sealing if they are sufficiently moist, as can be judged by the infiltration of liquid droplets through the packing.
- Engine overheating.
- The repair technology is violated, for example, not all sealing rings are replaced.
In addition to problems with seals, pump failures occur due to insufficient accurate centering of the housing and power unit. In this case, both seals and bearings are destroyed, leading to the failure of the unit, and only a major overhaul solves such problems.
Also, the lack of proper care for bearings (their regular lubrication) can be a threat.
You may be interested in the article on the classification of centrifugal pumps.
Read the article on centrifugal self-priming water pumps.
