Preparing to start the centrifugal pump. Centrifugal cantilever and submersible chemical pumps. Steam direct acting pumps
All work on preparation for start-up, start-up and shutdown of the centrifugal pump is carried out by order of the shift supervisor or shift supervisor.
Launch preparation. When preparing a centrifugal pump for start-up, after reviewing the entries in the shift log, it is necessary to check the connection of instrumentation, the presence of lubrication in the bearings, the technical condition of the clutch with the engine, the presence and serviceability of the protective shield on it, the grounding of the electric motor and starter.
If a centrifugal pump sucks liquid, then before starting the pump and the suction pipe are filled with the pumped liquid. If the pump is flooded or the liquid is supplied under pressure, then it is filled with liquid by opening the valve on the suction pipeline.
When the pumped liquid is installed above the level, the pump can be filled in one of the following ways:
open the valve on the bypass line from the discharge pipeline, while turning off the vacuum gauge to avoid damage;
suck air and vapors from the pump and the suction pipeline, for which the pump is connected to a vacuum pump or ejector;
pour liquid through a funnel; before filling the pump, open the taps to release air or vapors from the casing.
In the case of water-cooled bearings and seals, before starting the pump, fill in water by opening the taps on the corresponding pipelines. Before starting low-performance pumps, manually rotate the shaft by removing the guard on the engine coupling.
Pump start. Carried out with a closed valve on the pressure pipeline. When starting the pump, fully open the valve on the suction pipe, the pressure gauge valve and start the engine. When the pump reaches full speed and the pressure gauge shows the correct pressure, open the vacuum gauge cock and gradually open the valve on the pressure pipe. In order to avoid heating the liquid, the operation of the pump with the discharge valve closed (idling) should last no more than 2-3 minutes.
For normal operation of the pump, its almost silent stroke is characteristic.
Stop pump. It is necessary to stop the pump in the following sequence: slowly close the valve on the pressure pipeline; close the valve of the vacuum gauge (pressure gauge); stop the engine; close the valve on the suction pipeline; close the pressure gauge valve; release the pump from the pumped liquid, if it is provided by the instruction.
Maintenance of a running pump. Bearings must be lubricated while the pump is running. With ring lubrication of bearings, the rings must rotate freely with the shaft, maintain a normal level of lubricant in the crankcase. It is also necessary to maintain the normal temperature of the bearings. Every 800-1000 hours of pump operation, the used oil should be drained from the bearing housings, washed and filled with fresh oil. The driver must monitor the technical condition of the seals. Hydraulic sealing glands must be tightened so that the liquid leaks out continuously in separate drops. During the operation of the pump, it is necessary to maintain the specified mode, to record the readings of instrumentation in a replaceable log. The pump must not operate during cavitation. If it occurs, turn off the pump and check the suction line.
The driver is obliged to strictly comply with the rules of safety and labor protection.
When operating hermetically sealed electric pumps, it is categorically forbidden to: put the electric pump into operation if there is no certainty that it is completely filled with liquid and all air, gas or steam has been removed from it; break the flow of the pumped liquid to write suction; to carry out the initial start-up of the electric pump during installation or repair without first checking the insulation resistance of the stator winding relative to the housing; start the electric pump with the valve on the suction line closed; operate the electric pump without installing control and blocking devices specified in the operational documents; leave pumped liquid and coolant in the switched off electric pump, if they can change their state of aggregation at a temperature environment; operate the electric pump without cooling it.
In progress centrifugal pumps there may be malfunctions that the driver must eliminate. The pump "may fail to operate after start-up due to: leaks in the suction line - inspect the pipeline and eliminate leaks; presence of air or liquid vapor in the pump housing - refill the pump; clogging of pipes and vessels - inspect, clean pipes and vessels.
Feed during operation may decrease for the following reasons:
the rotational speed has decreased - check the mains voltage and the engine, eliminate the detected defects;
air seeps into the suction line or into the pump housing through the stuffing boxes - check the pipeline, tighten or change the packing of the stuffing box;
resistance has increased in the discharge and suction pipelines - check all valves and places of possible blockages in pipelines, clean them;
the impeller is clogged - inspect and clean it.
The pressure during operation may decrease due to:
decrease in speed - check the engine and, if faults are found, eliminate them;
air entering the pumped liquid - check the suction pipe;
fluid leaks - tighten or replace the gland packing;
damage to the pressure pipeline - close the valve on the pressure pipeline, inspect it and repair the damage;
worn sealing rings or damaged impeller - replace damaged parts.
Engine overload occurs: if the shaft run-up is too large, when the wheel rubs against the stationary parts of the pump, reduce the shaft run-up; with a large axial pressure - check the serviceability of the unloading devices and eliminate the detected defects; in case of clogging of internal parts, stop the pump, clean and flush the casing and impellers; when the pump flow increases above the allowable rate and the pressure is less than the calculated one, close the valve on the discharge pipeline.
Vibration and noise of the pump are caused by: weakening of the fundamental bolts - tighten the bolts; installation of the pump shaft and the electric motor is not on the same straight line - to make the correct alignment; partial clogging of the impellers - inspect and clean the pump; shaft deflection, sticking of rotating parts, wear of bearings - replace damaged parts; cavitation - stop the pump and take measures to reduce the suction head.
Occupational safety when working on pumping units. At the operator's workplace, safe working conditions must be created: the distances between the pumping units must provide free access and the ability to monitor the operation of the pump; stairs and ladders should be comfortable, lighting should be good, ventilation and heating should be sufficient.
The driver must comply with the following rules: to be at the workplace in special clothing; have at the workplace and, if necessary, use rubber gloves, goggles, a gas mask of a certain type and brand; make sure that moving and rotating parts of the machine are protected; when the pump is running, do not tighten bolts and studs on moving parts and do not replace seals and valves; avoid leakage of flammable and poisonous liquids; do not scatter oiled cleaning materials, but store them in metal closed boxes; always have a rubber mat near the starting electrical equipment; as portable lighting, use a portable lamp with a voltage of 12 V, and in some workshops only an explosion-proof one; know where fire extinguishers are stored and be able to use them; be able to call the fire brigade and gas rescuers; know and accurately follow the driver's job instructions.
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Hydraulics. Thermodynamics
Hydraulics is one of the areas of the unified science of fluid mechanics, called technical hydromechanics, which studies the issues of equilibrium and movement of various fluids. The laws of hydraulics are widely used in many areas of technology.
This material includes sections:
Properties of liquids
Information from hydrostatics and hydrodynamics
Practical use of the laws of hydrostatics and hydrodynamics
Fluid flow through holes and nozzles
Gas condition parameters
Ideal and real gases
Heat capacity of gases
First law of thermodynamics
Thermodynamic processes
Second law of thermodynamics
Water vapor properties
Moist air properties
Expiration and throttling
Fundamentals of heat transfer
The main assembly units of pipelines
The principle of operation and the device of pipeline fittings
Repair and testing of pipelines and fittings
Rules for the safe operation of pipelines and fittings
Drawing and reading piping diagrams
Volumetric pumps. General information
Reciprocating pumps
The main assembly units of the pump
Suction and discharge processes
gas caps
Piston pump indicator chart
Dosing and synchrodosing electric pump units
Steam direct acting pumps
Examples of drawing up and reading diagrams of pumping units
dynamic pumps. General information
Scheme of installation of centrifugal pumps
Main Parameters of Centrifugal Pump
Euler equation for determining the theoretical and actual heads of a centrifugal pump
Characteristics of centrifugal pump and pipeline
Collaboration of centrifugal pumps
Axial force and ways to unload it
The main assembly units of centrifugal pumps
Horizontal single wheel and multistage centrifugal pumps
Centrifugal cantilever and submersible chemical pumps
Centrifugal sealed electric pumps. Pumps made of non-metallic materials
Typical schemes of pumping units
General provisions for the operation of pumps
Regulation and lubrication of pumps
Automatic control of pumping units
Before launch the pump should be inspected (make sure that nothing interferes with the start-up), check the fastening, turn the impeller shaft by hand, open the air cock on the pump housing, open the suction valve. If the pump non-self-priming and works with suction, prime the suction pipe if the pump self-priming- fill in the vacuum attachment.
Pump start produce with the discharge valve closed; close the air valve as soon as water appears from it; slowly open the discharge valve.
Pump Maintenance during operation is to monitor the readings of instruments: pressure gauge, vacuum gauge, ammeter.
o Fluctuations of the manometer needle indicate the presence of air in the discharge pipeline, and a sharp increase in the ammeter reading indicates mechanical malfunctions inside the pump (if the manometer reading remains unchanged);
o monitor the condition of the glands, check the flow of fluid to the hydraulic seals (if any);
o Periodically open the air cocks on the pump body.
If a malfunction occurs in the operation of the pump, it should be stopped, the malfunctions identified and eliminated.
Pump stop produce in sequence:
Ä stop the engine;
Ä close the discharge and suction valves,
Ä Close the water cooling taps for the bearings (if any).
Faults that occur in centrifugal pumps are detected by a decrease or interruption in the supply of liquid, abnormal noise and vibration, excessive heating of individual parts, an increase in power consumption.
If at work innings pump decreases or stops, the reason for this may be:
¨ air leakage through the intake pipe or stuffing box,
¨ clogging of the receiving grid or kingston,
¨ increase in the gap between the impeller and the pump housing,
¨ reduction in the speed of the impeller,
¨ an increase in the temperature of the pumped liquid.
Vibration and knocking in the pump is usually caused by improper assembly or poor alignment with the drive motor.
Heating of individual parts or the entire pump can occur due to excessive or uneven compression of the stuffing box, insufficient lubrication or contaminated oil, prolonged operation with a closed discharge valve, or improper operation of the unloader disc (where present). Incorrect operation of the unloading disc is usually associated with contamination of the outlet tube from the unloading chamber to the inlet pipe - this tube should be cleaned.
The reasons for the increase in the power consumed by the pump (as indicated by the ammeter) may be:
¨ start the pump with the discharge valve open,
¨ high viscosity of pumped liquid,
¨ the thrust pressure is not balanced due to incorrect operation of the unloader,
¨ mechanical damage to bearings or shaft.
When comparing centrifugal and piston pumps it can be concluded that the former have a smaller mass and dimensions, because directly driven by high-speed electric or turbo motor, and uniform feeding. Due to the small number of parts in the device, a centrifugal pump is easier to maintain; it is less sensitive to the purity of the pumped liquid, since there are no working valves, it has lower hydraulic losses during suction.
but centrifugal pumps do not have dry suction, so they must be equipped with special vacuum attachments to ensure self-priming. For this, apply water ring or vortex auxiliary pumps. In centrifugal pumps, it is impossible to regulate the flow regardless of the generated pressure; therefore, they are not used in conditions of operation with variable flow at constant, high pressure especially if the feeds are small.
Features of operation of centrifugal pumps.
1 feature - centrifugal pumps, unlike piston ones, are not self-priming. To ensure the supply of liquid, it is necessary to install a suction apparatus (vortex pump) or manually fill the flowing part of the pump and the suction pipeline with the pumped liquid.
Feature 2 - centrifugal pumps, unlike piston pumps, supply liquid continuously and evenly. The pump is started with the suction valve open and the discharge valve slightly open.
Feature 3 - centrifugal pumps without suction units are always installed below the liquid level (with back pressure).
4 feature - because Since these pumps are mainly rotary type, they are dynamically balanced.
VORTEX PUMPS
Peripheral pumps are a type of vane pumps. The wheel disk has 1 milled radial blades. The cylindrical body has suction 2 and discharge 8 nozzles (Fig. 37, but), which are separated by a partition 4. When the wheel rotates, the liquid moves with the blades along the annular channel 5. The gaps between the ends of the wheel and the walls of the housing, as well as the partition and the wheel rim, are 0.2-0.5 mm.
Under the influence centrifugal force and rotation of the blades, a particle of liquid occupies successively positions BUT, IN And D, moving in a spiral (Fig. 37, b). She participates in relative motion with speed ω
, portable jointly with wheel rim with speed u and gains absolute speed from, equal to the geometric sum of the components, velocities.
Fig.37. vortex pump: but- scheme of the device; in- flow diagram of the fluid in the pump
When used in marine systems, peripheral pumps are often coupled with centrifugal pumps; they have a common housing and drive shaft for impellers.
Centrifugal vortex pump type ESN(Fig. 38) has wheel 1, which is connected by channel 2 to the volute of the centrifugal pump housing 3. When the wheel of the vortex pump rotates, a vacuum is created, which ensures the suction of air from the cavity of the suction pipeline of the centrifugal pump and its operation without preliminary filling of the intake pipeline.
Fig.38. Scheme of a centrifugal vortex pump type ESN
The ESN-1/1 pump (Fig. 39) is a unit that combines a horizontal two-stage centrifugal vortex pump with flange drive motor. The housing 2 at the top is made in the form of a hollow cap, to which the discharge pipeline is attached. Inserts 13 are located in the body, forming working chambers. A suction pipe 16 with a flange 1 is attached to the body. The impeller 15 is mounted on an extension 4 of the shaft 3 of the electric motor. The stuffing box seal consists of a bronze thrust bearing 6, a steel heel 7, a spring 10, a bronze bushing 9, a rubber sealing ring 8, a thrust ring 11 against which the spring abuts. Pin 17 fixes the position of the inserts. Plugs 12 and 14 are used to drain water. The extension is attached to the shaft with pin 5.
Fig.39. Centrifugal vortex pump ESN-1/1
Rules for the maintenance of vortex pumps the same as for centrifugal. The initial start-up is carried out after filling the body with liquid. This is not required for subsequent starts.
Vortex pump flow, m³/s,
Q = 0,5Fu ,
where F- cross-sectional area of the annular channel, m 2 ;
u- circumferential velocity of the liquid at the outer edge of the blade, m/s.
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Preparation of pumps for repair must be carried out in accordance with the conditions of work specified in the work order. At the same time, the unit must be stopped, its shut-off valves (gate valves and gates) must be set to a position that ensures safe work. Valve actuators must be locked with chains or other devices that exclude erroneous actions of personnel.
Preparation of pumps and a pumping unit for operation consists in checking the technical condition of the pumps and the pumping unit, the availability of the necessary equipment and its fastening, the presence of lubricant, the condition of the seals, and the condition of the shut-off and control valves.
The preparation of the pump for repair using hot work is carried out in the following sequence: the pump is stopped, the valves on the intake and pressure lines are closed, the excess pressure in the pump cavity is reduced to atmospheric, the pump is released from the flammable liquid, it is disconnected from the active lines with plugs, the pump is washed and steamed , open it.
The procedure for preparing pumps for start-up, shutdown and operation are detailed in job descriptions for jobs. It must be remembered that the start-up of a piston pump with a closed valve on the discharge pipeline and the operation of a centrifugal pump in an unstable, so-called cavitation mode, are not allowed. During cavitation, shocks appear in the pump, which create specific noise, crackling and vibration. At the same time, productivity and pressure decrease, impeller blades are destroyed, accidents and fires at installations are inevitable.
When preparing the pump for start-up, it is necessary to check the presence and connection of instrumentation, the presence of grease on the bearings, the condition of the coupling connection with the motor, the presence and serviceability of the protective shield on it, the grounding of the electric motor and the starter.
When preparing the pump for start-up, it is necessary to close the valves at the pressure gauge and vacuum gauge. The pump is started with the valve on the discharge pipeline closed. When the pump is started, the valve at the pressure gauge is opened. When the pump develops total number revolutions, and the pressure gauge will show the corresponding pressure, open the valve at the vacuum gauge, and then the valves on the pipelines that supply water to the glands. If there is a supply of cooling water to the bearings, open the corresponding taps. After that, the valve on the pressure pipeline is gradually opened. During operation, make sure that the oil rings rotate freely with the shaft and that the temperature of the bearings does not exceed the temperature in the machine room by more than 40 - 50 ° C; maintain the oil level in the bearings at the required height and change it after 800 - 1000 hours of pump operation; tighten the seals in a timely manner, comply with safety regulations.
When preparing the pump for start-up, it is necessary to check the presence and connection of instrumentation, the presence of grease on the bearings, the condition of the coupling connection with the motor, the presence and serviceability of the protective shield on it, and the grounding of the electric motor and starter.
When preparing the pump for start-up, the tightening of all fasteners is checked, dust and dirt are removed from their surface, and the pipeline lubrication systems are blown with compressed air. Then, through the grid, oil is poured into the pump crankcase, gearbox and gear couplings, and the tightness of the seals is checked. The clutch is manually driven, while the rotation of the rotor or crankshaft and the stroke of the pistons or plungers of the pump must be smooth and without jerks. Pumps intended for pumping hot liquids are heated with steam before starting, the temperature of which can be 40 ° C lower than the temperature of the pumped liquid.
During the preparation of the pump for start-up, the operator, who monitors the relevant part of the technological scheme of the installation, prepares the starting circuit for piping the unit. Simultaneously with the preparatory work, the electrician on duty must check the connection diagram of the electric motor. When using a steam turbine as a drive, preparation for launch depends on its type and brand and is carried out in accordance with the instructions: t; manufacturer's water.
During the preparation of the pump for start-up, the operator, who monitors the relevant part of the technological scheme of the installation, prepares the starting circuit for piping the unit. Simultaneously with the preparatory work, the electrician on duty must check the connection diagram of the electric motor. When used as a drive for a steam turbine, preparation for start-up depends on its type and brand and is carried out in accordance with the manufacturer's instructions.
During the preparation of the pump for start-up, the operator, who monitors the relevant part of the technological scheme of the installation, prepares the unit piping scheme. Simultaneously with the preparatory work, the electrician on duty must check the connection diagram of the electric motor.
Simultaneously with the preparation of the pump for start-up, preparations are made for starting the engine. Check the grounding of the motor and starter, as well as lubrication. In large electric motors, cables and windings are also checked.
Simultaneously with the preparation of the pump for start-up, preparations are made for starting the engine.