How to select pump type, series and model for Ultrasonic Machine

Selection condition

(1) Physical and chemical properties of the conveying medium

The physical and chemical properties of the conveying medium directly affect the performance, material and structure of the pump, which is an important factor to be considered when selecting. The physical and chemical properties of the medium include: medium name, medium characteristics (such as corrosion, abrasive, toxicity, etc.), solid particle content and particle size, density, viscosity, vaporization pressure, etc. If necessary, the gas content in the medium should also be listed, indicating whether the medium is easy to crystallize.

(2) Process parameters

Process parameters are the most important basis for pump selection, and should be carefully determined according to the process flow and operating range.

a) Flow Q flow refers to the quality of the pump required in the production of the process plant, and the workers should generally give the normal, minimum and maximum flow.

Only normal and rated flow rates are often given on the pump data sheet. When selecting a pump, the rated flow rate is required to be no less than the maximum flow rate of the device, or 1.1 to 1.15 times the normal flow rate.

b) Head H refers to the head value required by the process device, also known as the calculated head. Generally, the rated lift of the pump is 1.05 to 1.1 times the lift required by the device.

c) Inlet pressure Ps and outlet pressure Pd Inlet and outlet pressure refers to the pressure at the inlet and outlet nozzle flange of the pump, and the size of the inlet and outlet pressure affects the pressure resistance of the shell and the requirements of the shaft seal.

d) Temperature T refers to the temperature of the inlet medium of the pump, and the normal, minimum and maximum temperature of the inlet medium of the pump should generally be given during the process.

e) Device cavitation allowance NPSHa is also known as effective cavitation allowance.

f) Operation state The operation state is divided into continuous operation and intermittent operation.

(3) Site conditions

Site conditions include the installation location of the pump (indoor and outdoor), ambient temperature, relative humidity, atmospheric pressure, atmospheric corrosion status and classification of dangerous areas.

Selection of Pump type

The type of pump should be reasonably selected according to the process parameters of the device, the physical and chemical properties of the conveying medium, the operating cycle and the structural characteristics of the pump. Figure L-2 is the block diagram of pump type selection, which can be used for reference when selecting. According to the block diagram, the pump type that meets the requirements of device parameters and medium characteristics can be preliminarily determined. Centrifugal pump has the advantages of simple structure, no pulsation in infusion, simple flow regulation, etc., so in addition to the following circumstances, centrifugal pump should be selected as far as possible.

(1) When there are metering requirements, choose metering pump.

(2) When the head requirements are very high, the flow is very small and there is no suitable small flow high head centrifugal pump available, the reciprocating pump can be selected; If the cavitation requirement is not high, the vortex pump can also be selected.

(3) When the head is very low and the flow is very large, axial flow pumps and mixed flow pumps can be selected.

(4) When the medium viscosity is large (greater than 650 ~ 1000mm2 / s), you can consider choosing a rotor pump or reciprocating pump; When the viscosity is particularly large, specially designed high-viscosity rotor pump and high-viscosity reciprocating pump can be used.

(5) Gas content of medium > When the flow rate is small and the viscosity is less than 37.4mm2 / s, the vortex pump can be used. If the flow rate is allowed to pulsate, a reciprocating pump can be used.

(6) For frequent start-up or inconvenient irrigation pumps, pumps with self-priming performance should be selected, such as self-priming centrifugal pumps, self-priming vortex pumps, positive displacement pumps, etc.

Selection of series and materials of Pump

Pump series refers to pump factory production of the same type of structure and purpose of the pump, such as Is type clean pump, Y type oil pump, ZA type chemical process pump, SJA type chemical process pump and so on. When the type of pump is determined, the pump series and materials can be selected according to the process parameters and medium characteristics. If the centrifugal pump is selected, the following items can be further considered:

(1) According to the characteristics of the medium to decide which characteristics of the pump, such as clean pumps, corrosion resistant pumps, or chemical process pumps and impurity pumps and so on. When the medium is highly toxic, valuable or radioactive substances that are not allowed to leak, it should be considered to use non-leakage pumps (such as shield pumps, magnetic pumps) or double-end mechanical seals with leakage liquid collection and leakage alarm devices. If the medium is volatile liquid such as liquefied hydrocarbons, low cavitation margin pumps should be selected, such as barrel pumps.

(2) Choose horizontal pump, vertical pump (liquid pump, pipeline pump) according to the site installation conditions.

(3) According to the flow size, choose single suction pump, double suction pump, or small flow centrifugal pump.

(4) Select single-stage pump, multistage pump, or high-speed centrifugal pump according to the height of the head.

After the above is determined, the appropriate pump series and production plant can be selected according to the characteristics of different series of pumps in various types of pumps and the conditions of the production plant. If you decide to choose a single-stage horizontal chemical process pump, you can consider the SJA type of Shenyang pump factory, CZ type, ZA type of Dalian acid pump factory, and IH type of domestic general design chemical process pump and so on. Finally, according to the characteristics of the device and the technical parameters of the pump, decide which kind of manufacturing and inspection standards to choose. If the requirements are high, the API610 standard can be selected, and if the requirements are general, the GB5656(1SO5199) or ANSI 73.1m standard can be selected.

If the metering pump is selected, the following items can be further considered:

(1) When the medium is flammable, explosive, highly toxic and valuable liquid, diaphragm metering pump is often used. In order to prevent accidents caused by mixing of medium and hydraulic oil when diaphragm breaks, double diaphragm metering pump with diaphragm break alarm device can be selected.

(2) Flow regulation is generally manual, if automatic regulation is required, electric or pneumatic regulation can be selected.

Determination of pump type

After the type, series and material of the pump are selected, the pump model (that is, the specification) can be determined according to the sample and relevant information provided by the pump factory.

(1) Determination of positive displacement pump model

a) Determination of rated flow rate Q and rated outlet pressure resin required by the process

Rated flow Q generally adopts the maximum flow rate directly. If the maximum flow rate is missing, take 1.1 to 1.15 times of the normal flow rate. Rated outlet pressure P refers to the maximum possible pressure value at the pump outlet.

b) Check the flow rate [Q] and pressure [P] given by the positive displacement pump sample or technical data

Flow [Q] refers to the maximum flow output of a positive displacement pump. The flow rate required by the process can be achieved by bypass regulation and change of stroke. Pressure [P] refers to the maximum outlet pressure allowed by the positive displacement pump.

c) Selection criteria

If the following conditions are met, the pump model is preliminarily determined.

Flow Q≤[Q], and the closer Q is to [Q], the more reasonable it is. The pressure P≤ [P], and the closer P is to [P], the more reasonable.

e) Check the cavitation allowance of pump

The required NPSHr of the pump is less than the NPSHa of the device. If it does not meet this requirement, the installation height of the pump should be lowered to increase the NPSHa value. Or request the pump factory to reduce the NPSHr value; Or adopt the above two methods at the same time, and finally make NPSHr< (NPSHa- Safety Margin S).

When more than one type of pump meets the above conditions, a pump with high efficiency, low price and high reliability should be considered comprehensively.

(2) Determination of centrifugal pump model

a) Determination of rated flow and head

The rated flow is generally directly used the maximum flow, such as the lack of maximum flow value, usually take 1.1 to 1.15 times of the normal flow.

The rated lift is generally 1.05 ~ 1.1 times the lift required by the device. For media with viscosity > 20mm2 / s or containing solid particles, it is necessary to convert the rated flow rate and head when transporting water, and then perform the following work.

b) Look up the series spectrum

According to the rated flow and head to find the initial selection of pump model, may be 1, may also be more than 2,

c) Check

Check whether the rated working point of the pump falls within the high efficiency working area of the pump according to the performance curve; Check that the pump's device cavitation allowance NPSHa and the required cavitation allowance NPSHr meet the requirements. When it cannot be met, effective measures should be taken to achieve it.

When there are more than 2 specifications that meet the above conditions, the pump model with the highest comprehensive index should be selected as the final selection. Specifically, the following parameters can be compared: efficiency (high pump efficiency is best), weight (light pump weight is best) and price (low pump price is best).