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How to use the pump correctly & how to choose a pump?

How to use the pump correctly & how to choose a pump?

A water pump is a machine that transports liquids or pressurizes liquids. It transfers the mechanical energy of the prime mover or other external energy to the liquid to increase the energy of the liquid. It is mainly used to transport liquids including water, oil, acid and alkali liquids, emulsions, suspension emulsions and liquid metals.
It can also transport liquids, gas mixtures and liquids containing suspended solids. The technical parameters of pump performance include flow, suction, head, shaft power, water power, efficiency, etc.; according to different working principles, it can be divided into volumetric pumps, vane pumps and other types. Positive displacement pumps use changes in the volume of their working chambers to transfer energy; vane pumps use the interaction between rotating blades and water to transfer energy. There are centrifugal pumps, axial flow pumps and mixed flow pumps.

When choosing a water pump, many factors should be considered comprehensively.
1) Choose water pumps according to local conditions: There are 3 types of commonly used agricultural water pumps, namely centrifugal pumps, axial flow pumps and mixed flow pumps. The centrifugal pump has a high head, but the water output is not large, which is suitable for mountainous areas and well irrigation areas; the axial flow pump has a large water output, but the head is not too high, and is suitable for use in plain areas; the mixed flow pump has a water output and a head between the centrifugal pump Between the axial flow pump and the axial flow pump, it is suitable for plain and hilly areas. Users should choose according to the land conditions, water source and lifting height.
2) Select water pumps that exceed the standard appropriately. After determining the type of water pump, its economic performance should be considered, and special attention should be paid to the pump’s lift and flow rate and the selection of its supporting power. It must be noted that the head (total head) indicated on the pump label is different from the discharge head (actual head) when in 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 by 80% to 90% of the head and flow stated on the label. The power selection of the pump can be selected according to the power indicated on the label. In order to make the pump start quickly and use safe, the power machine is The power can also be slightly larger than the power required by the pump, generally about 10% higher; if you have power, you can choose a matching pump according to the power of the power machine when you buy a pump.

However, how to use the pump correctly?

According to the actual needs of irrigation and drainage, choose and determine the type and quantity of pumps that are compatible with the rated flow and rated head to ensure that the irrigation and drainage tasks can be completed efficiently and economically. The general method of selecting drainage and irrigation pumps is as follows:
① Determine the design flow of the pump.
②Determine the design head of the pump.
③ Determine the diameter of the pump.
④Determine the type of water pump.
⑤ Use “pump performance table” and “pump performance comprehensive spectrum” to select the pump model.
⑥Determine the number of pumps.

The power machine mainly adopts two categories: electric motor and diesel engine.
The main characteristics of the electric motor are: when the power is the same, the electric motor is smaller in size, lighter in weight, stable in operation, less vibration, simple in structure, the civil construction investment of the pump house is less, and the operation is simple, the maintenance is convenient, the work is reliable, and the operating cost is relatively low. Low, easy to realize automatic control. However, including power transmission and transformation equipment, the equipment investment is high, there must be power supply, and it is greatly affected by the grid voltage.
The main characteristics of the diesel engine are: it is not restricted by the power supply, easy to run at variable speeds, and is relatively mobile and flexible. However, its structure is more complicated, it is prone to malfunction, operation and maintenance are more troublesome, the requirements are higher, and the cost and operating cost are higher than those of the motor.
It can be seen that the two have their own advantages and disadvantages in comparison. Which type of power engine should be used should consider the conditions and characteristics of different regions, and choose the appropriate type according to local conditions.

In order to ensure the safe operation of the water pump, the water pump should be thoroughly and carefully inspected before the start of the unit, especially for the newly installed water pump or the pump that has not been used for a long time, pay more attention to the inspection work before the start, so as to find the problem and deal with it in time. The main inspection contents are as follows:
①Check whether the anchor bolts of the water pump and the power machine and the connecting bolts of various parts are loose or fall off, if any, they should be tightened or repaired.
② Rotate the coupling or pulley, check whether the impeller rotates flexibly, whether there is any abnormal sound in the pump, and judge whether the steering is correct. For a newly installed water pump, it is essential to check its steering when it is first started. For centrifugal pumps that are directly connected to the motor, check whether the direction of the pump is consistent with the direction sign arrow on the pump. If they are inconsistent, just exchange any two wires of the motor. If there is no sign arrow on the pump body, the pump casing is of volute type, which can be judged according to the shape of the pump, that is, the direction of rotation of the pump is consistent with the direction in which the volute increases; It can only be judged from the shape of the blade, that is, the pump should rotate along the direction of the blade’s curvature. For a centrifugal pump driven by a diesel engine, it can be judged directly based on the mutual position between the diesel engine and the water pump and the rotation mode used. Because the steering of the diesel engine is fixed counterclockwise from the power output end. If the steering is wrong, the transmission mode or the installation position of the diesel engine must be changed.
③Check whether the tightness of the packing gland is appropriate.
④Check the bearing lubrication, whether the lubricating oil is sufficient and clean, and whether the oil quantity meets the specified requirements.
⑤Clear the debris (blockages and floating objects) at the water inlet of the centrifugal pump to prevent the debris from being sucked into the pump after starting the machine and destroying the impeller.
⑥Check protection and safety work. Tools and other objects on the unit should be removed before starting to avoid being shaken off or causing unnecessary losses after starting.
⑦ Fill the centrifugal pump with water until the bleed plug on the pump body emits water.
⑧ Before starting the centrifugal pump, close the gate valve on the outlet pipe. Because the shaft power of the centrifugal pump is the smallest when the flow is zero, this will greatly reduce the load and resistance torque of the unit, which is convenient for a smooth start. Otherwise, it may be difficult to start the unit and even cause an accident.

When the water pump and the water inlet pipe are all filled with water, close the valve of the suction hole or the water filling device, and then start the power engine (electric motor or diesel engine). The outlet pipe of the centrifugal pump is generally equipped with a closed valve. After the unit is started up to the rated speed, the gate valve should be opened immediately to discharge the water, otherwise the water flow in the pump will continue to circulate in the pump casing and generate heat, which will cause certain zero of the pump. The component is damaged.
If the outlet of the centrifugal pump is equipped with a pressure gauge, it should be closed before starting. After the start, the water output is normal and then connected for measurement, so as to avoid that the pressure in the pump may exceed the range of the gauge when the gate valve is closed. damage.

① Pay attention to whether the unit has abnormal noise and vibration. When the centrifugal pump is in normal operation, the unit should be stable and the sound should be normal and continuous. If the unit has excessive vibration or noise, it indicates that the unit is malfunctioning. At this time, the unit should be stopped for inspection to eliminate hidden dangers.
②Pay attention to the inspection of bearing temperature and oil volume. During the operation of the centrifugal pump, a thermometer or a semiconductor point thermometer should be used to measure the temperature of the bearing and check whether the lubricating oil is sufficient. Generally, the maximum allowable temperature of sliding bearings can reach 85℃, and the maximum allowable temperature of rolling bearings can reach 90℃. In actual work, if there is no thermometer or semiconductor point thermometer, you can also touch the bearing housing with your hands. If you feel hot, it means the temperature is too high and you must stop the machine for inspection. Generally, too much or too little oil, too thick oil or mixed with other impurities can cause the bearing to heat up. The lubricating oil in the bearing should be moderate. For bearings lubricated with an oil ring, the oil ring is generally immersed for about 15mm. The ball bearings are lubricated with grease, and the grease should be added to about 1/3 of the capacity of the bearing box. The oil change time is generally 500h once, and the new water pump changes the oil in advance. The amount of oil refueling and the time of oil change can be carried out according to the regulations of the manufacturer.
③Check the temperature of the power machine. During the operation of the power machine, always pay attention to checking the temperature of the power machine. If the temperature is too high, it must be shut down immediately for inspection.
④Pay attention to whether the pump packing seal is normal. The packing should not be too tight or too loose. Water must drip out one after another during operation. According to experience, the water dripping from the packing culvert should be about 60 drops per minute. In addition, pay attention to whether the joints of the inlet pipe section are tight, and whether the inlet of the water pump is leaking.
⑤ Pay attention to the change of the indicator pointer. The instrument can best reflect the operation of the pumping device. Often the pump fails and there are signs on the instrument. Therefore, we should always pay attention to the conditions of various instruments. Generally, rural electric drainage and irrigation systems are equipped with ammeters, voltmeters and power meters, and some centrifugal pumps and mixed-flow pumps are also equipped with vacuum gauges and pressure gauges. If the operation is normal, the position of the indicator pointer is always stable at one position. If an abnormal situation occurs during operation, the meter will change and jump drastically, and the cause should be investigated immediately. For example, if the reading of the vacuum gauge rises, it may be that the water inlet pipe is blocked or the water level of the water source drops; the reading of the pressure gauge rises, it may be that the outlet pipe is blocked; the reading of the pressure gauge drops, it may be that the speed of the water pump is reduced due to belt slippage, or The water inlet pipe is leaking and air is sucked in, or the impeller is blocked. For the motor, when running under the required line voltage, the reading of the ammeter increases or decreases, which means the shaft power of the water pump increases or decreases. Therefore, attention should be paid to whether the reading of the ammeter exceeds the rated value, and long-term overload operation of the motor is generally not allowed.
⑥Pay attention to the changes in the water level of the inlet tank. If the water level of the inlet tank is lower than the specified minimum water level, the pump should be stopped to avoid cavitation and damage the pump impeller. If there is debris blocking the water inlet of the pump or in front of the trash rack in the pool, it should be removed immediately.