Principles and steps of pump selection: list the basic data and determine the flow head

Design Institute in the design of the device equipment, to determine the use and performance of the pump and select the pump type. This kind of choice must first choose the type and form of the pump, then what is the principle to choose the pump? What is the basis? We will analyze the principle for you below:

1. pump selection principle

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 medium characteristics:

For pumps that transport flammable, explosive, toxic or valuable media, shaft seals are required to be reliable or leak-free pumps, 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 IH stainless steel corrosion-resistant pumps, IHF fluorine plastic centrifugal pumps, and CQB fluorine plastic magnetic pumps.

For the pump conveying corrosive solid particle medium, it is required that the convection parts adopt wear-resistant and corrosion-resistant materials, and the shaft seal should be flushed with clean liquid when necessary. Optional UHB-ZK corrosion-resistant wear-resistant mortar pump

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 used as much as possible:

A., magnetic pump is selected for flammable, explosive, toxic or valuable medium and strong corrosive medium

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

C. When the head is very low and the flow is very large, axial flow pump and mixed flow pump can be selected.

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

E when the air content of the medium is 75%, the flow rate is small and the viscosity is less than 37.4 mm2/s, a vortex pump can be selected.

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 magnetic pump, pneumatic (electric) diaphragm pump

Selection basis of 2. pump

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.

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.

Basic data is listed 3:

1. Characteristics of medium: medium name, specific gravity, viscosity, corrosiveness, toxicity, etc.

2. The particle diameter and content of the body contained in the medium.

3. Medium temperature:(℃)

4. The required flow

General industrial pumps can ignore the leakage in the pipeline system in the process, but the impact on the flow rate must be considered when the process changes. If agricultural pumps use open channels for water delivery, leakage and evaporation must also be considered.

5, pressure: suction tank pressure, drain tank pressure, pressure drop in the pipeline system (head loss).

6. Pipeline system data (pipe diameter, length, type and number of pipe accessories, geometric elevation from suction tank to pressure tank, etc.).

If necessary, the device characteristic curve should also be made.

When designing and arranging pipelines, the following items shall be noted:

A, reasonable choice of pipe diameter, pipe diameter, in the same flow rate, the flow rate is small, the resistance loss is small, but the price is high, the pipe diameter is small, will lead to a sharp increase in resistance loss, so that the selected pump head increases, with increased power, costs and operating costs are increased. Therefore, it should be considered from a technical and economic point of view.

B. The discharge pipe and its pipe joints should consider the maximum pressure that can be withstood.

C, the pipeline layout should be arranged as straight pipe as far as possible, as far as possible to reduce the accessories in the pipeline and minimize the length of the pipeline, when it is necessary to turn, the bending radius of the elbow should be 3 to 5 times the diameter of the pipeline, the angle as far as possible greater than 90 ℃.

D. The discharge side of the pump must be equipped with valves (ball valves or globe valves, etc.) and check valves. The valve is used to adjust the operating point of the pump. The check valve can prevent the pump from reversing when the liquid flows back, and make the pump avoid the blow of water hammer. (When the liquid flows backwards, huge reverse pressure will be generated, which will damage the pump)

4. to determine the flow head, flow

A, if the production process has given the minimum, normal and maximum flow, should be considered according to the maximum flow.

If only the normal flow is given in the production process, a certain margin should be considered.

For large flow and low unintended lift pumps with ns>100, the flow margin shall be 5%, for small flow and high lift pumps with ns<50, the flow margin shall be 10%, for pumps with 50 ≤ns ≤ 100, the flow margin shall also be 5%, and for pumps with poor quality and bad operating conditions, the flow margin shall be 10%.

If the basic data is only given to the weight flow rate, it should be converted into the volume flow rate.