Buy the pump need to pay attention to what

The first step: to understand the pump selection principle 1, the type and performance of the selected pump should be consistent with the device flow, head (or pressure), temperature, NPSH, suction process parameters such as the request.

2. The characteristics of the conveying medium must be met.

For the physical properties of the transport medium similar to water, clean water pumps (single-stage, multi-stage, and mid-open pumps) can be used.

For pumps conveying flammable, explosive, toxic, or valuable media, shaft seals are required or leak-free pumps are used, such as magnetic drive pumps, diaphragm pumps, canned pumps, gear pumps, etc. Pumps for conveying corrosive media require convection parts Corrosion resistant materials are used, and the materials used are different for different media. Such as chemical pumps, stainless steel gear pumps.

For the transport of pumps containing solid particles, it is required to adopt wear-resistant materials for the flow-through parts and adopt special designs. If necessary, double-end mechanical seals are used and flushing and cooling with external cleaning liquids, such as slurry pumps and open pumps.

For conveying medium containing solid small particles, which has corrosiveness and a wide range of viscosity, a screw pump can be used.

3, mechanical reliability, low noise, vibration.

4. Comprehensively consider economically, so that the total cost is the lowest, such as equipment costs, operating costs, maintenance and management costs.

5, centrifugal pumps generally have high speed, small size, light weight, high efficiency, large flow, simple structure, no pulse, stable performance, easy operation and easy maintenance and so on. Therefore, centrifugal pumps should be used as much as possible except in the following cases:

When there are metering requirements, use a metering pump;

High head requirements, small flow rate and no suitable small flow high-lift centrifugal pump can be used, optional cavitation requirements can also be used when the vortex pump is not high;

When the lift is very low and the flow rate is large, axial and mixed-flow pumps can be used.

When the viscosity of the medium is larger (greater than 650~1000mm2/s), the rotor pump or reciprocating pump (gear pump, screw pump) may be considered;

When the medium gas content is 75%, the flow rate is small and the viscosity is less than 37.4mm2/s, the vortex pump can be selected;

For occasions with frequent startup or inconvenient filling, pumps with self-priming properties, such as self-priming centrifugal pumps, self-priming vortex pumps, and pneumatic (electric) diaphragm pumps, should be used.

The second step: Know the basic conditions of pump selection The basic conditions of pump selection should be based on the process flow, water supply and drainage requirements, considering from five aspects, namely the liquid delivery volume, device lift, liquid properties, piping layout and operation Operating conditions, etc. 1. Flow rate is one of the important performance parameters for pump selection. It is directly related to the production capacity and conveying capacity of the entire device. For example, in the process design of the design institute, the normal, minimum and maximum flow rates of the pump can be calculated. When the pump is selected, the maximum flow rate is taken as the basis and the normal flow rate is taken into consideration. When there is no maximum flow rate, it is usually possible to take 1.1 times of the normal flow rate as the maximum flow rate.

2. The required head of the device system is another important performance data of the pump selection. Generally, the head is selected after amplification with 5%-10% margin.

3, liquid properties, including the name of the liquid medium, physical properties, chemical properties and other properties, physical properties of temperature, density and viscosity, the diameter of solid particles in the medium and the gas content, etc., which relates to the system's lift, effective cavitation Quantity calculation and type of suitable pump; Chemical property, mainly refers to the chemical corrosivity and toxicity of liquid medium, is an important basis for selecting pump material and selecting shaft seal type.

4. Pipeline layout conditions of the installation system refer to the height of the transmission medium, the distance of the transmission medium and the direction of the transmission medium, the minimum liquid level on the suction side, the maximum liquid level on the discharge side, and some data and pipe specifications, lengths, materials, and pipe fittings specifications. , quantity, etc., in order to carry out system head calculation and NPSH check.

5, the operating conditions of many content, such as the liquid saturation vapor pressure, suction side pressure (absolute), the discharge side of the container pressure, altitude, ambient temperature, operation is a gap or continuous operation, the pump position is fixed or Removable and so on.

The third step: Select the specific operation of the pump According to the pump selection principle and basic conditions for selection, the specific operation is as follows:

1, according to the device layout, terrain conditions, water level conditions, operating conditions, determine the choice of horizontal, vertical and other types (pipeline, submersible, submerged, non-blocking, self-priming, gear, etc.) Pump.

2, according to the nature of the liquid medium, determine the clean water pump, hot water pump or oil pump, chemical pump or corrosion-resistant pump or impurity pump, or use non-clogging pump.

Pumps installed in explosive areas should be equipped with explosion-proof motors according to the level of the explosion zone.

3, according to the flow size, determine the menu suction pump or double suction pump; according to the level of lift, single-stage pump or multi-stage pump, high-speed pump or low-speed pump (air-conditioning pump), multi-stage pump efficiency lower than single-stage pump, such as When a single-stage pump and a multi-stage pump can be used, the single-stage pump is used first.

4, determine the specific model of the pump to determine the use of what series of pumps, you can press the maximum flow, (in the absence of maximum flow, you can usually take the normal flow of 1.1 times as the maximum flow), take 5% -10% after amplification The head of these two main parameters of the performance, in the spectrum or series of characteristics to determine the specific model. The operation is as follows:

Using the pump characteristic curve, find the desired flow value on the abscissa and find the required head value on the ordinate, and draw the vertical or horizontal line from the two values ​​up and to the right. The intersection of the two lines falls exactly on the characteristic curve. The pump is the pump to be selected, but this ideal situation is generally very small, usually encounter the following two conditions:

The first kind: the intersection point is above the characteristic curve. This shows that the flow rate meets the requirements, but the lift is not enough. At this time, if the heads are almost the same, or the difference is about 5%, they can still be used. If there is a lot of difference in the lift, the pump with a larger lift is selected. . Or try to reduce pipeline resistance loss.

The second type: the intersection point is below the characteristic curve. Within the range of the fan-shaped trapezoid of the pump characteristic curve, this model is preliminarily set, and then according to how much the head difference, to decide whether to cut the impeller diameter, if the head difference is very small, it will not be cut. The heads are quite different. According to their ns and cutting formulas, the diameter of the impeller is cut. If the intersection does not fall within the range of the fan-shaped trapezoid, the pump with a smaller lift should be selected.

When selecting a pump, sometimes the production process requirements must be taken into account, and different QH characteristic curves should be selected.

5, after the pump model is determined, the pump of the physical and chemical medium similar to the water pump or the transmission medium, need to go to the relevant product catalog or sample, according to the model performance table or performance curve correction, to see whether the normal working point falls in the Pump priority work area? Whether the effective NPSH is greater than (NPSH). Can also be reversed to NPSH correction geometry installation height?

6, for the delivery of liquid viscosity greater than 20mm2 / s liquid pump (or density greater than 1000kg/m3), must be the water test pump characteristic curve is converted to the viscosity (or the density) of the performance curve, especially for the suction performance and The input power is carefully calculated or compared.

7, determine the number of pumps and standby rate:

Normally only one pump is used for normal operation, because one large pump is equivalent to two small pumps working in parallel (refers to the head and the same flow rate). The efficiency of the large pump is higher than that of the small pump. Taiwan Tai pump, instead of two small pumps, but in the following cases, consider two pumps in parallel:

The flow rate is very high and one pump cannot reach this flow.

For large pumps that require a 50% standby rate, two smaller pumps can be changed and two spares (three in total)

For some large pumps, a 70% flow rate pump can be used in parallel to operate without a backup pump. When one pump is inspected, the other pump still takes 70% of the production.

For pumps that require 24 hours of continuous operation, spare three pumps, one for operation, one for standby, and one for maintenance.