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, Make the type and performance of the selected pump meet the requirements of process parameters such as device flow, head, pressure, temperature, cavitation flow, suction and so on.
　　
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 measurement requirements, the selection of metering pumps
　　
b, high lift, small flow and no suitable small flow high lift centrifugal pump can be used, you can choose reciprocating pump, such as cavitation less demanding can also use the vortex pump.
　　
c, low lift, large flow, 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, 75% gas content of the medium, the flow is smaller and the viscosity is less than 37.4mm2 / s, the optional 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 the basic basis for gear pump selection
　　
Gear pump selection basis, should be based on process, water supply and drainage requirements, to be considered from five aspects, namely liquid delivery capacity, device lift, liquid properties, piping layout and operating conditions.
　　
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
　　
Third, select the specific operation of gear pump
　　
According to pump selection principle and selection of basic conditions, the specific operation is as follows:
　　
1. According to the layout of equipment, topography, water level conditions and operating conditions, the choice of horizontal, vertical and other types (pipeline type, submersible type, submerged type, non-clogging type, self-priming type, 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
　　
After determining which pump to use, you can press the maximum flow, (in the absence of maximum flow, usually desirable 1.1 times the normal flow rate as the maximum flow), take up 5% -10% head lift capacity of these two The main parameters, in the spectrum or series of curves to determine the specific model. Operation is as follows:
　　
Use the pump characteristic curve to find the desired flow value on the abscissa and the desired lift value on the ordinate. Draw the vertical or horizontal line from the two values, respectively, right and left, and the intersection point of the two lines falls exactly on the characteristic curve. The pump is the pump of choice, but the ideal situation is usually very 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 the lift is not enough, this time, if the lift is about the same, or a difference of about 5%, can still be used, if the lift a lot of difference, . Or try to reduce the pipeline resistance loss.
　　
The second: the intersection point below the characteristic curve, in the fan characteristic trapezoidal trapezoidal range, it is initially set under this model, and then according to how much head difference, to decide whether to cut the impeller diameter,
　　
If the head difference is small, do not cut, if the head is a big difference, according to the required Q, H, according to its ns and cutting formula, cut the impeller diameter, if the intersection does not fall within the range of fan-shaped trapezoidal, Small pump. 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 1000kg / m3), be sure to test the pump characteristics of the water into the viscosity (or the density) of the performance curve, especially for the inhalation performance and Input power carefully calculated or more nuclear.
　　
7, determine the number of gear pump and spare rate:
　　
The 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 point of view of energy-saving options rather Ning Taiwan big pump, rather than two small pumps, but in the case of the following circumstances, consider the two pumps in parallel cooperation:
　　
A lot of traffic, a pump can not reach this traffic.
　　
For large pumps that require a 50% standby rate, two smaller pumps can be changed to work, two for backup (three in total)
　　
For some large pumps, pumps with a 70% flow rate can be used in parallel without a backup pump. When one pump is undergoing overhaul, the other pump still takes over 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:
　　
The 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 point of view of energy-saving options rather Ning Taiwan big pump, rather than two small pumps, but in the case of the following circumstances, consider the two pumps in parallel cooperation:
　　
A lot of traffic, a gear pump can not reach this flow.
　　
For large pumps requiring a 50% standby rate, two smaller pumps can be changed to work, with two spares (total of three)
　　
For some large pumps, the pump with 70% of the flow rate can be selected for operation in parallel without a spare pump. When one pump is undergoing maintenance, the other pump still takes 70% of the production.
　　
On the need for 24 hours of continuous operation of the pump, spare pump should be three, running, a spare, a maintenance.
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