When designing the plant and equipment, the design institute shall determine the purpose and performance of the pump and select the collapse type. This choice must first choose the type and form of the pump, then what principle to choose the pump? What is the basis?

1. understanding of pump selection principles

1. Make the type and performance of the selected pump meet the requirements of process parameters such as flow rate, head, pressure, temperature, cavitation flow rate, suction stroke, etc.

2, must meet the requirements of media characteristics.

For pumps conveying flammable, explosive, toxic or valuable media, reliable shaft seals or non-leakage pumps are required, such as magnetic drive pumps, diaphragm pumps and shielding pumps.

For pumps that transport corrosive media, it is required to use corrosion-resistant materials for convection components, such as AFB stainless steel corrosion-resistant pumps and CQF engineering plastics magnetic drive pumps.

Conveying of solid particle medium pump, requires the use of wear-resistant materials convection parts, if necessary, the shaft seal with clean liquid flushing.

3, high mechanical reliability, low noise, small vibration.

4, the economy to take into account the equipment costs, operating costs, maintenance costs and management costs of the lowest total cost.

5. The centrifugal pump has the characteristics of high speed, small size, light weight, high efficiency, large flow, simple structure, no pulsation in infusion, stable performance, easy operation and convenient maintenance.

Therefore, in addition to the following circumstances, the centrifugal pump should be selected as far as possible：

A, there are metering requirements, the selection of metering pump

B, head requirements are very high, the flow is very small and there is no suitable small flow high head centrifugal pump can be selected, reciprocating pump can be selected, such as cavitation requirements are not high, vortex pump can also be selected.

C, head is very low, large flow, can choose the axial flow pump and mixed flow pump.

D, medium viscosity is larger (greater than 650~1000 mm2/s), can consider the use of rotor pump or reciprocating pump (gear pump, screw pump)

E, medium air content 75%, flow and viscosity is less than 37.4 mm2/s, can choose vortex pump.

F, to start frequently or filling the pump inconvenient occasions, should be selected with self-priming performance of the pump, such as self-priming centrifugal pump, self-priming vortex pump, pneumatic (electric) diaphragm pump.

Second, know the basic basis for pump selection

Pump selection basis, should be based on the process, water supply and drainage requirements, from five aspects to be considered, both liquid delivery, device head, liquid properties, pipeline layout and operating conditions, etc.

1. The flow rate is one of the important performance data of the pump, which is directly related to the production capacity and conveying capacity of the whole device. For example, the design institute can calculate the normal, minimum and maximum flow rates of the pump in the process design. Select the pump, based on the maximum flow, taking into account the normal flow, in the absence of maximum flow, usually desirable 1.1 times the normal flow as the maximum flow.

2. The lift required by the device system is another important performance data for selecting pumps. Generally, the lift is selected after enlarging the margin by 5%-10%.

3. Liquid properties, including the name of liquid medium, physical properties, chemical properties and other properties. Physical properties include temperature c, density d, viscosity u, diameter of solid particles in medium and content of gas, etc. This involves the head of the system, calculation of effective cavitation allowance and type of suitable pump: chemical properties, mainly refers to the chemical corrosiveness and toxicity of liquid medium, it is an important basis for selecting pump materials and selecting shaft seal types.

4. The pipeline layout conditions of the device system refer to some data such as the lowest liquid level on the suction side and the highest liquid level on the discharge side, as well as pipeline specifications and their length, materials, pipe fittings specifications, quantity, etc., so as to calculate the head of the tie comb and check the NPSH.

5. There are many contents of operating conditions, such as the operation of liquid T saturated steam force P, suction side pressure PS (absolute), discharge side container pressure PZ, altitude, ambient temperature operation is gap or continuous, and the position of the pump is fixed or movable.

Specific operation of 3. selection pump

According to the pump selection principle and selection of basic conditions, the specific operation is as follows:

1, according to the layout of the device, terrain conditions, water level conditions, operating conditions, determine the choice of horizontal, vertical and other types (pipeline, submersible, submerged, non-clogging, 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.

For pumps installed in explosive areas, corresponding explosion-proof motors shall be used according to the grade of explosive areas.

3. According to the flow rate, determine whether to select a single suction pump or a double suction pump; according to the head, select a single-stage pump or a multi-stage pump, a high-speed pump or a low-speed pump (air conditioning pump), and the efficiency of a multi-stage pump is lower than that of a single-stage pump. If both single-stage pumps and multi-stage pumps can be used, first select a single-stage pump.

4. Determine the specific model of the pump

After determining which series of pumps to choose, the specific model can be determined on the type spectrum chart or series characteristic curve according to the maximum flow rate (when there is no maximum flow rate, 1.1 times of the normal flow rate is usually taken as the maximum flow rate) and the two main performance parameters of the lift after enlarging the margin of 5%-10%. The operation is as follows:

Using the pump characteristic curve, find the required flow value on the abscissa, find the required lift value on the ordinate, lead the vertical or horizontal line upward and rightward from the two values respectively, and the intersection of the two lines falls on the characteristic curve, then the pump is the pump to be selected, but this ideal situation is generally rare, and the following two situations are usually encountered:

The first is that the intersection point is above the characteristic curve, which indicates that the flow meets the requirements, but the lift is not enough. At this time, if the lift is similar, or the difference is about 5%, it can still be selected. If the lift is much different, the pump with larger lift is selected. Or try to reduce the pipeline resistance loss.

The second type: the intersection point is below the characteristic curve, and within the fan-shaped trapezoidal range of the pump characteristic curve, this model is initially determined, and then whether to cut the impeller diameter is determined according to the difference in lift,

If the lift difference is very small, it will not be cut. If the lift difference is very large, the impeller diameter will be cut according to the required Q, H, and ns and cutting formula. If the intersection point does not fall within the fan-shaped trapezoid range, the pump with smaller lift should be selected. When selecting a pump, it is sometimes necessary to consider the requirements of the production process and choose different shapes to Q-H the characteristic curve.

5. After the pump model is determined, the pump or the pump whose physical and chemical medium of the transmission medium is similar to water shall be corrected on the relevant product catalog or sample according to the performance table or performance curve of the model to see whether the normal working point falls in the priority working area of the pump and whether the effective NPSH is greater than (NPSH). Can NPSH be used in turn to correct the geometric installation height?

6. For liquid pumps with conveying viscosity greater than 20mm 2/s (or density greater than 1000kg/m3), it is necessary to convert the characteristic curve of water experimental pump into the performance curve of the viscosity (or under the density), especially to carefully calculate or compare the suction performance and input power.

7. Determine the number of pumps and standby rate:

Generally, only one pump is used for normal operation, because one large pump is equivalent to two small pumps working in parallel (referring to the same head and flow rate), and the efficiency of the large pump is higher than that of the small pump. Therefore, from the perspective of energy saving, it is better to choose one large pump instead of two small pumps. However, in case of the following situations, parallel cooperation of the two pumps can be considered:

The flow rate is very large, and a pump cannot reach this flow rate.

For some large pumps, pumps with 70% flow requirements can be selected for parallel operation without standby pumps. When one pump is overhauled, the other pump still undertakes 70% of the transportation in production.

For pumps that need to run continuously for 24 hours, three pumps should be standby, one for operation, one for standby and one for maintenance.

8. Under normal circumstances, customers can submit their "basic conditions for pump selection", and our company will select or recommend better pump products. If the design institute in the design of the device equipment, the pump model has been determined, according to the requirements of the design institute configuration.

9. Determine the number of pumps and standby rate:

Generally, only one pump is used for normal operation, because one large pump is equivalent to two small pumps working in parallel (referring to the same head and flow rate), and the efficiency of the large pump is higher than that of the small pump. Therefore, from the perspective of energy saving, it is better to choose one large pump instead of two small pumps. However, in case of the following situations, parallel cooperation of the two pumps can be considered:

The flow rate is very large, and a pump cannot reach this flow rate.

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

For some large pumps, pumps with 70% flow requirements can be selected for parallel operation without standby pumps. When one pump is overhauled, the other pump still bears 70% of the transportation in production.

For pumps that need to run continuously for 24 hours, three pumps should be standby, running, one standby and one maintenance.