Definition of water pump
Usually, machines that lift liquid, transport liquid or increase the pressure of liquid, that is, machines that convert the mechanical energy of the prime mover into liquid energy to achieve the purpose of pumping liquid are collectively called pumps.
2 Working principle of water pump
1 Positive displacement pump: uses the periodic change of the working chamber volume to transport liquid.
2 Vane pump: uses the interaction between vanes and liquid to transport liquid.
3 Specific uses of the pump
Pumps have different uses, different liquid media, different flow rates and lift ranges. Therefore, their structures and materials are also different. In summary, they can be roughly divided into:
1. Urban water supply 2. Sewage system 3. Civil engineering and construction system 4. Agricultural water conservancy system 5. Power station system 6. Chemical industry system 7. Petroleum industry system 8. Mining and metallurgy system 9. Light industry system 10. Ship system
4 Pump Type Classification
1. Classification according to the working principle of the pump:
1. Centrifugal pump 2. Vortex pump 3. Mixed flow pump 4. Axial flow pump 5. Electric pump 6. Steam pump 7. Gear pump 8. Screw pump 9. Roots pump 10. Vane pump 11. Jet pump 12. Lifting pump 13. Electromagnetic pump 14. Submersible pump, etc.
(II) Classification by purpose:
1. Clean water pump, 2. Slurry pump, 3. Sewage pump, 4. Chemical pump, 5. Oil pump, etc.
(III) Other division methods:
There are many other ways to classify water pumps: according to whether the impellers are connected in series, they are divided into single-stage and multi-stage pumps; according to whether the water pump has one or two suction inlets, they are divided into single-suction pumps and double-suction pumps, and so on.
Six common faults of water pumps and their solutions
1 Unable to start
First, check the power supply: whether the joint connection is reliable; whether the switch contact is tight; whether the fuse is blown; whether the three-phase power supply is missing a phase. If there is a circuit break, poor contact, fuse blown, or missing phase, the cause should be found out and repaired in time. Secondly, check whether it is a mechanical failure of the water pump itself. Common reasons include: the packing is too tight or the impeller and the pump body are stuck and blocked by debris; the pump shaft, bearings, and leakage rings are rusted; the pump shaft is severely bent, etc. Troubleshooting methods: loosen the packing, dredge the water diversion trough; disassemble the pump body to remove debris and rust; remove the pump shaft for correction or replace a new pump shaft.
2. The matching power motor is overheated
There are four reasons. The first is the power supply: the voltage is too high or too low. Under a specific load, if the voltage fluctuation range is outside the rated value of +10% to -5%, it will cause the motor to overheat; the three-phase voltage of the power supply is asymmetrical, and the phase imbalance of the three-phase voltage of the power supply exceeds 5%, which will cause the winding to overheat; the lack of phase operation, experience shows that more than 85% of agricultural motors are burned due to lack of phase operation, and the motor should be installed with a lack of phase protection device. The second is the reason for the water pump: the power is not matched, the small horse pulls the big cart, the motor is overloaded for a long time, and the motor temperature is too high; the start is too frequent, and the motor with a short-term or intermittent working system is continuously working. The number of starts should be limited, the thermal protection should be selected correctly, and the motor should be used according to the rated value marked on the motor. The third is the cause of the motor itself: the connection method is wrong, the △ shape is mistakenly connected to the Y shape, which causes the temperature of the motor to rise rapidly; the stator winding has phase-to-phase short circuit, turn-to-turn short circuit or local grounding, the motor is partially overheated in mild cases, and the insulation is burned in severe cases; the squirrel cage rotor is broken or defective, the motor runs for 1 to 2 hours, and the core temperature rises rapidly; the ventilation system fails, and the fan should be checked for damage, the direction of rotation is correct, and the ventilation duct is blocked; the bearing wear and the eccentric sweeping of the rotor cause the stator and rotor cores to rub against each other and make a metal collision sound, and the core temperature rises rapidly. In severe cases, the motor smokes and even the coil burns. The fourth is the cause of the working environment: the motor winding is damp or dust, oil, etc. are attached to the winding, resulting in reduced insulation. The insulation resistance of the motor should be measured and cleaned and dried; the ambient temperature is too high. When the ambient temperature exceeds 35°C, the high inlet temperature will cause the temperature of the motor to be too high, and efforts should be made to improve its working environment. Such as building a shed for sunshade. Note: If a failure occurs due to electrical reasons, you should ask an electrician with a professional qualification certificate to repair it. People with only a limited knowledge should not repair it blindly to prevent personal injury accidents.
3. Water pump heating
Causes: bearing damage; too small clearance between rolling bearing or bracket cover; bent pump shaft or misalignment of two shafts; too tight tape; lack of oil or poor oil quality; blockage of balance hole on impeller, causing impeller to lose balance and increase thrust to one side. Troubleshooting methods: replace bearing; remove rear cover, add gasket between bracket and bearing seat; check pump shaft or adjust concentricity of two shafts; loosen tape tightness appropriately; add clean butter, butter accounts for about 60% of the gap in bearing; clear blockage in balance hole.
4 Insufficient flow
This is because: the power speed is not matched or the belt slips, causing the speed to be low; the axial flow pump blade installation angle is too small; the head is insufficient, the pipeline is too long or the pipeline has a right-angle bend; the suction distance is too high; the bottom valve, pipeline and impeller are partially blocked or the impeller is defective; the outlet pipe leaks seriously. Troubleshooting method: restore the rated speed, remove the belt grease, adjust the belt tightness; adjust the blade angle, lower the installation position of the water pump, shorten the pipeline or change the curvature of the pipeline; seal the leaking part of the water pump and compress the packing; remove the blockage and replace the impeller; replace the leakage reduction ring and block the leaking part.
5. Cannot absorb water
The reason is that there is air in the pump body or air is accumulated in the water inlet pipe, or the bottom valve is not closed tightly and the water is not fully filled, the vacuum pump packing is seriously leaking, and the gate valve or flap valve is not closed tightly. Troubleshooting method: First press the water up, then fill the pump body with water, and then start the machine. At the same time, check whether the check valve is tight, whether there is air leakage in the pipeline and joints. If air leakage is found, apply lubricating oil or mixed paint on the joints after disassembly, and tighten the screws. Check the oil seal ring of the water pump shaft. If it is severely worn, replace it with a new one. The pipeline is leaking water or air. The nut may not be tightened during installation. If the leakage is not serious, you can apply cement or cement slurry mixed with asphalt oil to the leaking place. Temporary repairs can be applied with some wet mud or soft soap. If there is water leakage at the joint, you can tighten the nut with a wrench. If the leakage is serious, you must disassemble and reassemble it and replace the cracked pipe; reduce the head and press the pipe mouth of the water pump into the water 0.5m.
6 Severe vibration
There are mainly the following reasons: unbalanced electric rotor; poor coupling; worn and bent bearings; loose and broken parts of rotating parts; weak pipe brackets, etc. These can be dealt with by adjustment, repair, reinforcement, straightening, replacement, etc.
The above situations are common causes of water pump failure, but not all the causes. When dealing with faults in practice, we should follow the principle of outside first and inside later based on actual analysis, and never operate blindly.
Cavitation phenomenon of water pump
The cavitation of water pump is caused by the vaporization of water. The so-called vaporization is the process of water changing from liquid to gas. The vaporization of water has a certain relationship with temperature and pressure. Under a certain pressure, when the temperature rises to a certain value, water begins to vaporize; if the pressure drops to a certain value at a certain temperature, water will also vaporize. This pressure is called the vaporization pressure of water at that temperature. If the pressure in a certain local area is equal to or lower than the vaporization pressure corresponding to the water temperature during the flow process, water will vaporize at that location. After vaporization occurs, many small bubbles of steam and gas will be formed. When the bubbles flow from the low-pressure area to the high-pressure area along with the water flow, the bubbles burst under the action of high pressure, and the high-pressure water flows to the space occupied by these original bubbles at a very high speed, forming an impact force. Under the action of water hammer pressure, the metal surface forms fatigue and is severely damaged. Therefore, we call the entire process of bubble formation, development and rupture, which leads to material damage, the cavitation phenomenon.
Causes of water pump vibration
Analysis of the causes of water pump vibration There are many reasons for the vibration of the unit and pump room building. Some factors are both related and interact with each other. In summary, there are mainly four reasons.
1 Electrical aspects
The motor is the main equipment of the unit. The imbalance of magnetic force inside the motor and the imbalance of other electrical systems often cause vibration and noise. For example, when an asynchronous motor is running, the radial alternating magnetic pull between the stator and rotor generated by the interaction of the harmonic magnetic flux of the stator and rotor teeth, or when a large synchronous motor is running, the magnetic center of the stator and rotor is inconsistent or the air gap difference in each direction exceeds the allowable deviation value, etc., which may cause the motor to vibrate periodically and make noise.
2 Mechanical aspects
Unbalanced mass of the rotating parts of the motor and pump, shoddy workmanship, poor installation quality, asymmetric axis of the unit, swing exceeding the allowable value, poor mechanical strength and rigidity of the components, wear and damage of bearings and sealing components, and resonance caused by the critical speed of the pump and the natural frequency of the unit will all cause strong vibration and noise.
3 Hydraulic aspects
Uneven distribution of flow velocity and pressure at the pump inlet, pressure pulsation of the working liquid at the pump inlet and outlet, liquid bypass, deviation and separation, non-rated working conditions and cavitation of the pump caused by various reasons are all common causes of vibration of the pump unit. Rapid changes in pressure and water hammer in the water pipeline caused by dynamic transition processes such as pump startup and shutdown, valve opening and closing, working condition changes and emergency shutdown due to accidents also often cause vibration in the pump room and unit.
4 Water conservancy and other aspects
The unreasonable design of the unit’s water inlet flow channel or the incompatibility with the unit, the improper immersion depth of the water pump, and the unreasonable start-up and shutdown sequence of the unit will deteriorate the water inlet conditions, generate vortices, induce cavitation, or increase the vibration of the unit and pump room. When starting a unit that uses a siphon-breaking vacuum interrupter, if the hump section has difficulty entraining air, the siphon formation time is too long; the unit’s flap door design is unreasonable, it opens and closes from time to time, and constantly hits the flap door seat; the foundation supporting the water pump and motor sinks unevenly or the foundation has poor rigidity, etc., which will also cause the unit to vibrate.
Pump selection
When users choose water pumps, it is best to go to sales outlets approved by the agricultural machinery department and be sure to identify the manufacturer. It is recommended to give priority to buying water-filled submersible electric pumps and to check the brand and product quality certificate. Do not buy “three-no” products (i.e. no manufacturer, no production date, no production license), otherwise if problems arise, users will be helpless.
As a user, it is difficult to make a decision due to the limitation of professional knowledge. The best way is to consult experts in water pumps, and also consult some old water pump users, especially those who use similar conditions to yourself. It is a wise choice to buy products that these users trust, have reliable quality and are relatively mature. At the same time, the decision to use a single-phase pump or a three-phase pump should be made based on the local power supply conditions.
Select a pump that meets the head requirements
The so-called head refers to the required head, not the water lifting height. It is particularly important to clarify this point when choosing a water pump. The water pump head is about 1.15 to 1.20 times the water lifting height. For example, if the vertical height from a water source to the water use point is 20 meters, the required head is about 23 to 24 meters.
When choosing a water pump, the head on the pump nameplate should be close to the required head, and the general deviation should not exceed 20%. In this case, the water pump has the highest efficiency, is more energy-saving, and is more economical to use. If the head on the nameplate is much smaller than the required head, the water pump often cannot meet the needs of the user. Even if it can pump water, the amount of water is pitifully small. But on the other hand, when a high-head water pump is used for a low head, the flow rate will be too large, causing the motor to overload. If it runs for a long time, the motor temperature will rise, the winding insulation layer will gradually age, and even burn the motor.
Choose a pump with the right flow rate
The flow rate of the water pump, that is, the water output, should not be too large, otherwise it will increase the cost of purchasing the water pump. It should be selected according to the needs. For example, if the user uses a self-priming water pump for home use, the flow rate should be as small as possible; if the user uses a submersible pump for irrigation, a larger flow rate can be appropriately selected.
Key points for choosing agricultural water pumps
1. Choose water pumps according to local conditions. There are three types of commonly used agricultural water pumps, namely centrifugal pumps, axial flow pumps and mixed flow pumps. Centrifugal pumps have a higher head but a small water output, and are suitable for mountainous areas and well irrigation areas; axial flow pumps have a larger water output but a lower head, and are suitable for use in plain areas; the water output and head of mixed flow pumps are between centrifugal pumps and axial flow pumps, and are suitable for use in plain and hilly areas. Users should choose according to local terrain conditions, water sources and water lifting height.
2. It is necessary to select a water pump that exceeds the standard appropriately. After determining the type of water pump, its economic performance should be considered, and special attention should be paid to the selection of the head and flow rate of the water pump and its supporting power. It must be noted that the head (total head) indicated on the water pump label is different from the water discharge head (actual head) during use. This is because there will be a certain resistance loss when the water flows through the water pipe and the vicinity of the pipeline. Therefore, the actual head is generally 10%-20% lower than the total head, and the water output is also reduced accordingly. Therefore, in actual use, it can only be estimated according to 80% to 90% of the head and flow rate indicated on the label. The selection of supporting power for the water pump can be selected according to the power indicated on the label. In order to make the water pump start quickly and use it safely, the power of the power machine can also be slightly greater than the power required by the water pump, generally about 10% higher; if there is already power, when purchasing a water pump, you can choose a matching water pump according to the power of the power machine.
3. Strict procedures must be followed when purchasing water pumps. When purchasing, the “three certificates” must be checked, namely the agricultural machinery promotion license, production license and product inspection certificate. Only when the three certificates are complete can we avoid purchasing obsolete products and inferior products.
Pump parameters
1. Traffic Q
Flow rate is the amount of liquid (volume or mass) delivered by the pump per unit time.
The volume flow rate is represented by Q, and the unit is: m3/s, m3/h, l/s, etc.
Mass flow is represented by Qm, and its unit is: t/h, kg/s, etc.
The relationship between mass flow rate and volume flow rate is:
Qm=ρQ
Where ρ is the density of the liquid (kg/m3, t/m3), and the normal temperature water ρ=1000kg/m3.
2. Lift H
The head is the energy increment of the unit weight of liquid pumped by the water pump from the pump inlet (pump inlet flange) to the pump outlet (pump outlet flange). That is, the effective energy obtained by one Newton of liquid passing through the pump. Its unit is Nm/N=m, that is, the height of the liquid column pumped by the pump, usually referred to as meter.
3. Speed n
The speed is the number of revolutions of the pump shaft per unit time, represented by the symbol n, and the unit is r/min.
4. NPSH
NPSH, also known as net positive suction head, is the main parameter to indicate cavitation performance. NPSH was once expressed as Δh in China.
5. Power and efficiency
The power of a water pump usually refers to the input power, that is, the power transmitted from the prime mover to the pump shaft, so it is also called shaft power, represented by P;
The effective power of the pump is also called the output power, which is represented by Pe. It is the effective energy obtained by the liquid transported from the pump in the pump per unit time.
Because the head refers to the effective energy obtained from the pump per unit weight of liquid output by the pump, the product of the head, mass flow rate and gravitational acceleration is the effective energy obtained from the liquid output from the pump per unit time – that is, the effective power of the pump:
Pe = ρgQH(W) = γQH(W)
Where ρ is the density of the liquid pumped by the pump (kg/m3);
γ–weight of the liquid delivered by the pump (N/m3);
Q–pump flow rate (m3/s);
H–pump head (m);
g–acceleration due to gravity (m/s2).
The difference between shaft power P and effective power Pe is the power loss in the pump, and its magnitude is measured by the pump efficiency. The pump efficiency is the ratio of effective power to shaft power, represented by η.
What is flow? What letters are used to represent it? How to convert it?
The volume of liquid discharged by the pump per unit time is called flow rate, which is represented by Q. The measurement unit is: cubic meter per hour (m3/h), liter per second (l/s), L/s=3.6 m3/h=0.06 m3/min=60L/min
G=Qρ G is weight ρ is liquid specific gravity
Example: A pump has a flow rate of 50 m3/h. What is the weight of water pumped per hour? The specific gravity of water is ρ 1000 kg/m3.
Solution: G=Qρ=50×1000(m3/h.kg/ m3)=50000kg/h=50t/h
What is head? What letter is used to represent it? What unit of measurement is used? How to convert it to pressure and what formula is used?
The energy obtained by a unit weight of liquid passing through a pump is called head. The head of a pump includes the suction head, which is approximately the pressure difference between the pump outlet and the pump inlet. The head is represented by H, and the unit is meter (m). The pressure of a pump is represented by P, and the unit is MPa (megapascal), H=P/ρ. If P is 1kg/cm2, then H=(lkg/cm2)/(1000kg/m3) H=(1kg/cm2)/(1000kg/m3)=(10000kg/m2)/1000kg/m3=10m 1Mpa=10kg/c m2,H=(P2-P1)/ρ (P2=outlet pressure P1=inlet pressure)
What is NPSH? What is suction lift? What are the letters representing their respective units of measurement?
When the water pump is working, the liquid will produce gas at the inlet of the impeller due to a certain vacuum pressure. The vaporized bubbles will erode the metal surface of the impeller and other metals under the impact movement of the liquid particles, thereby destroying the impeller and other metals. At this time, the vacuum pressure is called the vaporization pressure. The NPSH refers to the surplus energy of the unit weight of liquid at the pump suction port that exceeds the vaporization pressure. The unit is marked in meters, using (NPSH) r. The suction distance is the required NPSH Δh: that is, the vacuum degree that the pump allows to absorb liquid, that is, the allowable installation height of the pump, in meters.
Suction head = standard atmospheric pressure (10.33 meters) – cavitation margin – safety margin (0.5 meters)
Standard atmospheric pressure can create a pipeline vacuum height of 10.33 meters.
For example: The required NPSH of a pump is 4.0 meters. What is the suction head Δh?
Solution: Δh = 10.33-4.0-0.5 = 5.83 meters
Standard for Multi-function Pump Control Valve
The standard technical requirements are introduced as follows:
Pressure-temperature level
The pressure-temperature rating of the multifunctional water pump control valve is determined by the pressure-temperature rating of the shell, internal parts and control pipe system materials. The maximum allowable working pressure of the multifunctional water pump control valve at a certain temperature is the smaller value of the maximum allowable working pressure values of the shell, internal parts and control pipe system materials at that temperature.
1. The pressure-temperature rating of the iron shell shall comply with the requirements of GB/T17241.7.
2. The pressure-temperature grade of the steel shell shall comply with the requirements of GB/T9124.
3. For materials whose pressure-temperature grades are not specified in GB/T17241.7 and GB/T9124, the relevant standards or design requirements may apply.
Valve body
1 Valve body flange
The flange should be cast as a whole with the valve body. The type and size of the iron flange should comply with the provisions of GB/T17241.6, and the technical conditions should comply with the provisions of GB/T17241.7; the type and size of the steel flange should comply with the provisions of GB/T9113.1, and the technical conditions should comply with the provisions of GB/T9124.
2. Minimum wall thickness of valve body
The minimum wall thickness of cast iron valve body shall comply with the provisions of Table 3 in GB/T13932-1992, and the minimum wall thickness of cast steel valve body shall comply with the provisions of Table 1 in JB/T8937-1999.
Valve cover diaphragm seat
1. The connection between the valve cover and the diaphragm seat, and between the diaphragm seat and the valve body should be flange type.
2. The number of connecting bolts between the diaphragm seat and the valve body shall not be less than 4.
3. The minimum wall thickness of the valve cover and diaphragm seat shall comply with the requirements of 2.3.
4. The flanges between the valve cover and the diaphragm seat should be circular. The flange sealing surface can be flat, raised or concave-convex.
Valve stem, slow closing valve plate, main valve plate
1 The slow closing valve plate and valve stem should be connected tightly and reliably.
2. The sealing type between the slow closing valve plate and the main valve plate should be metal sealing type.
3. The main valve plate and valve stem must slide flexibly and reliably.
4. The seal between the main valve plate and the main valve plate seat can be of two types: metal seal and non-metal seal.
Diaphragm
1.The appearance quality of the diaphragm shall comply with the requirements of HG/T3090.
2. When used for drinking water, the safety of the diaphragm material shall comply with the requirements of GB/T17219.
Control pipe system
Each component of the control pipe system should be able to withstand the maximum working pressure of the valve, and no leakage should occur in any part.
Materials
1. The selection of materials for main components should comply with the requirements of JB/T5300.
2. Copper alloy castings shall comply with the provisions of GB/T12225; grey cast iron castings shall comply with the provisions of GB/T12226, and their tensile strength shall not be less than 200MPa; ductile iron castings shall comply with the provisions of GB/T12227; carbon steel castings shall comply with the provisions of GB/T12229; austenitic steel castings shall comply with the provisions of GB/T12230.
3. The appearance quality of steel multi-function water pump control valve castings shall comply with the provisions of JB/T7927, and the appearance quality of iron multi-function water pump control valve castings shall refer to the provisions of JB/T7927.
Shell strength
The shell strength of the multi-function water pump control valve shall comply with the requirements of GB/T13927.
Sealing performance
The sealing performance of the multi-function water pump control valve shall comply with the requirements of GB/T13927.
Cleanliness
The cleanliness of the multi-function water pump control valve shall comply with the requirements of JB/T7748.
Painting
When used for drinking water, the safety of the coating material of the inner cavity of the multi-function pump control valve shall comply with the provisions of GB/T17219. There is no regulation for the coating of the outer surface, and special requirements shall be indicated in the order contract.
