The choice of a pump, the user chooses the pump, it is best to the agricultural machinery department approved point of sale, we must recognize the manufacturer. It is recommended to give priority to the purchase of water-filled submersible pumps, and to see the grades and product quality certification. Do not buy three no (that is, no manufacturer, no production date, no production license) products, otherwise there is a problem, the user will be at a loss what to do. As a user, due to the limitations of professional knowledge, it is difficult to decide, the best way is to consult the pump experts, may wish to consult some of the older pump users, especially those who are close to their own conditions, to buy these users trust, Reliable quality and more mature products, after all, a wise choice. At the same time, should be based on local power supply situation to decide with single-phase pump or three-phase pump. 2. Choose pump to meet the head lift The so-called head lift is the required lift, rather than lifting the water level, it is clear that the choice of pump is particularly important. Pump lift about 1.15 to 1.20 times the height of the lift. If a water source to the water vertical height of 20 meters, its required lift is about 23 to 24 meters. The pump should be selected on the pump nameplate lift the best and the desired head close to the general deviation of not more than 20%, in such cases, the highest efficiency of the pump, but also more energy-efficient, the use of more economical. If the nameplate lift is far less than the required head, the pump often can not meet the needs of users, even if the pumping water, the water is also small pitiful. However, when the pump with high head is used for low lift, the flow will be too large, causing the motor to over load. If the motor is running for a long time and the motor temperature rises, the winding insulation will gradually age and even burn the motor. 3. Select the appropriate flow rate of the pump flow, that is, the amount of water out of the general election should not be too large, otherwise it will increase the cost of purchasing a pump. Should be selected according to need, such as self-suction pumps used by the user's home, the flow should be selected as small as possible; such as user irrigation submersible pumps, you can choose the appropriate flow larger. 4. The key to the purchase of agricultural water pump 1) to local conditions to buy water pump. Commonly used agricultural pumps have three types, namely centrifugal pumps, axial pumps and Francis pumps. Centrifugal pump higher head, but the water is not large, suitable for mountain and well irrigation area; axial pump large amount of water, but the lift is not too high, suitable for use in plain areas; Francis pump water and head lift between the centrifugal pump And axial flow pump, suitable for plain and hilly areas. Users should according to the local conditions, water and water to buy height. 2) to be properly exceeded the election pump. After determining the type of pump, to consider its economic performance, with particular attention to the pump head and flow and the choice of supporting power. It must be noted that there is a difference between the head (total head) indicated on the pump label and the head of water (actual head) when it is used, as there is a certain loss of resistance when the water flows through the pipe and the pipe. Therefore, the actual head is generally 10% -20% lower than the total head, the amount of water is also reduced accordingly. Therefore, the actual use, only by the signs of the head and flow rate of 80% to 90% estimated that the pump supporting the power of choice, according to the signs indicated on the power of choice, in order to make the pump start quickly and use safety, power machine Power can be slightly larger than the pump power required, generally higher than about 10% is appropriate; if there is power, when purchasing a pump, you can press the power of the power machine to buy matching pump. 3) To strictly purchase water pump. When purchasing the three certificates to be tested, that is, agricultural machinery to promote permits, production licenses and product inspection certificate, only three cards all can avoid the purchase of obsolete products and inferior products. Second, the selection process According to the selection principle and selection of pump basic conditions, the specific operation is as follows: 1, according to the layout of the device, topography, water conditions, operating conditions, to determine the choice of horizontal, vertical and other types (pipeline, Submersible, submerged, non-clogging, self-priming, gear-type, etc.) pumps. 2, according to the nature of the liquid medium, to determine installed in the explosive area of ​​the pump, explosion area should be based on the level of the corresponding explosion-proof motor. 3, according to the size of the flow, to determine whether the suction pump menu or double suction pump; according to the level of the pump, single-stage pump or multi-stage pump, the same can be used, the first choice of single-stage pump. 4, to determine the specific type of pump to determine what series of pumps to choose, you can press the maximum flow, (in the absence of maximum flow, usually desirable 1.1 times the normal flow as the maximum flow), take 5% -10% margin Lift the main parameters of these two properties, to determine the specific model in the spectrum or series of characteristic curves. The operation is as follows: Use the pump characteristic curve, find the required flow value on the abscissa, find the required lift value on the ordinate, from the two values ​​were drawn up and down, respectively, vertical or horizontal line, intersection of two lines just fall in the characteristic curve , Then the pump is the pump to be selected, but this ideal situation is generally small, usually encounter the following two situations: The first: the intersection point in the characteristic curve above, indicating that the flow to meet the requirements, but not enough head, this When the lift is almost the same, or a difference of about 5%, can still be used, if a lot of head difference, then choose a larger head pump. Or try to reduce the pipeline resistance loss. The second: the intersection of the curve below the characteristic curve, in the fan characteristic trapezoidal trapezoidal range, initially set this model, and then according to head difference between how much to decide whether to cut the impeller diameter, if the head difference is small, do not cut, if According to the required Q and H, according to its ns and cutting formula, cut the impeller diameter, if the intersection does not fall within the range of fan-shaped trapezoid, should choose a pump with smaller head. Pump selection, and sometimes have to consider the production process requirements, choose different shape QH characteristic curve. 5, the pump model is determined, the pump or transport medium near the water of the physical and chemical pump, need to go to the relevant product catalogs or samples, according to the model performance chart or performance curve correction to see whether the normal working point falls on the Pump priority work area? The effective NPSH is greater than (NPSH). You can also reverse the geometric installation height by NPSH 6. For liquid pumps with a viscosity greater than 20mm2 / s (or more than 1000kg / m3), you must convert the water test pump characteristic curve to that viscosity (or at this density) Performance curve, in particular, on inhalation performance and input power should be carefully calculated or more nuclear. 7, to determine the number of pumps and spare rate: For normal operation of the pump, generally only one, because a large pump and parallel work of two small pumps, (referring to the head, the same flow), the pump efficiency is higher than the small Pump, so from the perspective of energy-saving rather choose a large pump, rather than two small pumps, but in the following cases, consider the two pumps in parallel cooperation: a large flow, a pump can not reach this flow. For large pumps requiring a 50% standby rate, two smaller pumps can be changed and two spares (totaling three) can operate in parallel for some large pumps with a choice of 70% flow rate, without a backup pump, When one pump is undergoing maintenance, the other pump still carries 70% of the production. On the need for 24 hours of continuous operation of the pump, spare pump should be three, one running, a spare, a maintenance. 8, under normal circumstances, the customer can submit the basic conditions of its election pump, given by the Division I choose or recommend better pump products. If the design institute in the design of equipment, the pump model has been determined, according to the design institute requirements configuration. 9, to determine the number of pumps and spare rate: For normal operation of the pump, generally only one, because a large pump and parallel work of two small pumps, (referring to the head, the same flow), the pump efficiency is higher than the small Pump, so from the perspective of energy-saving rather choose a large pump, rather than two small pumps, but in the following cases, consider the two pumps in parallel cooperation: a large flow, a pump can not reach this flow. For large pumps requiring a 50% back-up rate, two smaller pumps can be changed to work with two spares (for a total of three). For some large pumps, a pump with a 70% flow rate can be used in parallel without a backup pump, When one pump is undergoing maintenance, the other pump lift still assumes 70% of the delivery on production. On the need for 24 hours of continuous operation of the pump, spare pump should be three, running, a spare, a maintenance.