Design Institute equipment in the design, to determine the purpose and performance of the pump and choose the collapse type. This choice must start with the choice of pump type and form, then what is the principle to choose gear pump? What is the basis? First, understand the principle of gear pump selection 1, the type and performance of the selected pump in line with the device flow, head, pressure, temperature, cavitation flow, suction stroke and other process parameters. 2, must meet the characteristics of the media requirements. Pumps that deliver flammable, explosive toxic or valuable media require dependable shaft seals or leak-free pumps such as gear pumps, magnetically driven pumps, diaphragm pumps, shielded pumps. Conveying medium for the pump, convection parts require corrosion-resistant materials, such as fluorine plastic corrosion-resistant pump, CQF engineering plastic magnetic drive pump. Pumps containing solid particulate media are required to have a wear-resistant material for the convection components and flush with a cleaning fluid if necessary. 3, high mechanical reliability, low noise, small vibration. 4, the economic should take into account the equipment costs, operating costs, maintenance costs and management fees the lowest total cost. 5, centrifugal pump with high speed, small size, light weight, high efficiency, large flow, simple structure, infusion without pulsation, stable performance, easy operation and maintenance features such as convenience. Therefore, in addition to the following circumstances, the centrifugal pump should be used as far as possible: a, a metering requirements, the selection of metering pumps b, high lift requirements, flow is small and not suitable for small high-flow centrifugal pump can be used when optional reciprocating pump , Such as cavitation requirements can also be used less whirlpool pump. C, low lift, flow is large, the choice of axial flow pump and mixed flow pump. d, medium viscosity (greater than 650 ~ 1000mm2 / s), consider the choice of rotor pump or reciprocating pump (gear pump, screw pump) e, medium gas content of 75%, the flow rate is smaller and the viscosity is less than 37.4mm2 / s When, can choose vortex pump. f, on the occasion of frequent start or pump inconvenience occasion, should use self-priming pump performance, such as self-priming centrifugal pump, self-priming vortex pump, pneumatic (electric) diaphragm pump. Second, we know that the basic selection of gear pump Gear pump selection basis, should be based on process, water supply and drainage requirements, to be considered from five aspects, both liquid delivery capacity, the device lift, liquid properties, piping layout and operating conditions Wait. 1, the flow rate is one of the important performance of the election pump data, which is directly related to the entire plant's production capacity and delivery capacity. Such as the design process can be calculated in the pump normal, minimum, maximum three kinds of flow. Select the pump, based on the maximum flow, take into account the normal flow, in the absence of the maximum flow, it is usually desirable 1.1 times the normal flow as the maximum flow. 2, the lift system required for installation of the pump is another important performance data, generally to enlarge the 5% -10% head lift to choose. 3, the liquid properties, including the name of the liquid medium, physical properties, chemical properties and other properties, the physical properties of the temperature c density d, viscosity u, medium particle diameter and gas content, etc., which involves the system lift, effective gas Erosion margin calculation and the type of suitable pump: Chemical nature, mainly refers to the liquid medium chemical corrosion and toxicity, is the selection of pump materials and choose an important basis for the type of shaft seal. 4, the installation of piping system conditions refers to the liquid from the height of the liquid into the liquid distance to the suction side such as the lowest level, the highest level of the discharge side of some data and pipe specifications and length, material, pipe specifications, the number , Etc., in order to carry out the Department of combing head calculation and NPSH check. 5, the operating conditions are many, such as the operation of the liquid T saturated steam P, suction side pressure PS (absolute), the discharge side of the tank pressure PZ, altitude, ambient temperature operation is gap or continuous, the pump position is fixed Or removable three, the specific operation of the selection of gear pump pump selection principles and selection of 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, submersible, non-clogging, self-priming, gear-type, etc.) pump. 2, according to the nature of the liquid medium to determine the water pump, hot water pump or pump, chemical pump or corrosion-resistant pump or impurity pump, or non-clogging pump. Pumps installed in the explosive area should be based on the explosion area level, using the appropriate explosion-proof motor. 3, according to the size of the flow, to determine the menu suction pump or double suction pump; according to the level of the head, single-stage pump or multi-stage pump, high speed pump or low speed pump (air conditioning pump) Single-stage pump and multi-stage pump can also be used when the first choice of single-stage pump. 4, Determine the specific type of gear pump to determine the choice of what series of pumps, you can press the maximum flow, (in the absence of maximum flow, it is usually desirable to 1.1 times the normal flow as the maximum flow), take 5% -10% margin After the lift of the two main parameters of performance, in the spectrum or series of characteristic curve to determine the specific model. 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). Can also be reversed in order to NPSH geometric installation height? 6, for the delivery of liquid viscosity greater than 20mm2 / s (or density greater than 10