First, understand the principles of pump selection

     1 , so that the selected pump type and performance in line with unit flow, head, pressure, temperature , cavitation flow , suction process parameters such requirements.

     2, must meet the requirements of dielectric characteristics .

     For transportation of flammable , explosive toxic or valuable medium pumps require reliable seal with no leakage pump , such as magnetic drive pumps, diaphragm pumps , shielding pumps.

     A pump for conveying corrosive media , requiring convective parts are corrosion-resistant materials, such as stainless steel corrosion resistant AFB , CQF plastic magnetic drive pumps.

     Medium for conveying solid particles containing a pump , requiring convective parts are wear-resistant materials , if necessary, with the adoption of cleaner liquid seal flush .

     3, the mechanical aspects of high reliability, low noise , small vibration .

     4 , the economy and comprehensive consideration to the equipment costs , operating costs, maintenance costs and the lowest total cost of management fees

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     Therefore, the following exceptions should be used wherever possible centrifugal pumps :

a, a measurement requirements , the selection of metering pumps

b, head demanding, traffic is very small and not suitable for low flow high head pumps can be used , the choice of reciprocating pump , such as less demanding when cavitation vortex pump can also be used .

c, head low, traffic is heavy , the choice of axial and mixed flow pumps.

d, medium viscosity ( greater than 650 ~ 1000mm2 / s) , can be considered optional rotor pump or reciprocating pump ( gear pump , screw pump )

e, medium containing 75% of gas , flow is small and the viscosity of less than 37.4mm2 / s , the choice of vortex pump .

f, frequent or irrigation pump for start inconvenience occasions , should be used with self- priming pump , such as self- priming centrifugal pumps , self-priming vortex pump , pneumatic ( electric ) diaphragm pumps.

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Second, know the fundamental basis for pump selection

     Pump selection basis , should be based on process , drainage requirements, from five aspects to be considered , not only the amount of liquid delivery , installation head , the liquid nature of the piping and the operating conditions , etc.

     1 , the pump flow was selected one of the important performance data , which is directly related to the production capacity of the entire device and transmission capacity . Such as process design institute is able to calculate the pump is normal, minimum, maximum, three kinds of traffic. Select the pump at maximum flow rate as the basis, taking into account the normal flow , in the absence of maximum flow , it is usually desirable to 1.1 times the normal traffic flow as the maximum .

     2, the device system required pump head is selected another important performance data , the general use of amplification after 5% -10% margin to lift selection .

     3 , the liquid nature of the liquid medium including name, physical properties , chemical properties and other properties , physical properties with temperature c density d, viscosity u, medium diameter of solid particles and gas content, etc. , which relate to the lift system , the effective gas NPSH calculations and suitable pump types: chemical properties , mainly referring to the liquid medium corrosive and toxic chemicals , is the choice of materials and choice of what kind of pump shaft seal type of important basis.

     4 , the device piping system refers to a condition highly liquid feeding liquid from the liquid feed to send , such as suction side of the minimum level , the discharge side of the highest level and some data and pipe specifications and lengths , materials , fittings, specifications, quantity , in order to carry out the Department comb head NPSH calculations and checking .

     5, the operating conditions of many things, such as liquid saturated steam power operation T P, suction-side pressure PS ( absolute ) , the discharge side of the vessel pressure PZ, altitude , ambient temperature operation is a gap or continuous pump position is fixed thing can shift .

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Third, the specific operation of pump selection

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

     1, according to the device layout, terrain conditions , water conditions , operating conditions , determine the selection horizontal, vertical , and other types ( pipeline , diving , liquid-type , non-clogging , self -priming , gear , etc. ) of pumps.

     2, according to the nature of the liquid medium to determine the water pump, heat pump or pumps , chemical pumps or Naifushibeng or trash pump , or the use of non-clogging pumps.

      Pump installed in the blast area , regional level should be based on the explosion , with the corresponding proof motors.

     3 , according to the size of the flow , determine the menu or double suction pump suction pump ; according to lift the level , menu -stage pump or multistage pumps, high speed pump or low speed pump ( air pump ) , multistage pump more efficient than single-stage pump is low, such as menu pump and can use the same multi-stage pumps , the first choice of a single-stage pumps.

     4 to determine the specific type of pump

      Determine the selection of what the series after the pump , you can press the maximum flow ( in the absence of maximum flow , it is usually desirable to 1.1 times the normal traffic flow as the largest ) , whichever is magnified up to 5 % -10 % margin lift after the performance of these two the main parameters in the model spectrum or series of characteristic curves to determine the specific model . Operation is as follows:

      The pump characteristic curve, find the flow rate value on the horizontal axis , the vertical axis to find the required lift value , values from both up and right vertical or horizontal line arguments , intersection of two lines on the right on the curve , the the pump is to choose a pump , but this ideal situation rarely , usually run into the following two situations:

       The first: the top intersections in the characteristic curve , which shows traffic to meet the requirements , but the head is not enough, at this time , if the head similar, or a difference of about 5% , you can still choose from, a lot of difference if the head , then select larger pump head . Or try to reduce the pipeline pressure losses.

       The second: the intersection of the characteristic curves below the characteristic curve of the pump within the fan ladder , it initially set for this model, and then based on the difference in head , to decide whether to cut the impeller diameter ,

       If the head difference is small , do not cut, if the head big difference , just press the desired Q, H,, according to its formula ns and cutting , cutting impeller diameter , if the intersection does not fall within the scope of trapezoidal fan , to be elected head over small pumps. When selecting a pump , and sometimes have to consider the production process requirements , use of different shapes QH curve .

     5, the pump model is confirmed , the pump or the transmission medium of physical and chemical medium approximation water pump , the need for product catalogs or samples and then , on the basis of the performance curve model performance tables or corrections to see whether the normal operating point falls within the pump priority area ? Is greater than the effective NPSH (NPSH). NPSH can also turn to the geometric corrections to mounting height ?

     6, for liquids with a viscosity greater than 20mm2 / s liquid pump ( or density greater than 1000kg/m3), must take to the water pump characteristic curve experiment converted to the viscosity ( or the density ) of the performance curve , in particular, on the suction performance and input power for serious computing or representing nucleus.

     7 to determine the number of units and standby pump rate:

       On the normal operation of the pump , usually only one, because a large pump and two pumps working in parallel equivalent ( refer to head, flow the same ) , a large pump more efficient than small pump , so from an energy perspective rather Optional NTU pump instead of two small pumps , but any of the following situations , consider two pumps in parallel cooperation :

       Flows, a pump can not reach this traffic .

       50% of the need for large pumps standby rate , can be changed in two smaller pump , two spare ( of three )

       For some large pumps , the choice of 70% of the flow requirements of pumps in parallel operation , do not spare pump in a pump overhaul, another pump still bear 70% of the production of transport .

       On the need for 24 hours non-stop operation of the pump , you should spare three pumps , one running , one standby , one maintenance.

     8 , under normal circumstances , customers can submit their " basic condition for selecting a pump ," given by the Division I or recommend a better selection of pumps . If the institute in the design of plant equipment , the right pump model has been determined, according to institute requires configuration.

     9 , determine the number of units and standby pump rate: for the normal operation of the pump , usually only one, because a large pump and two pumps working in parallel equivalent ( refer to head, flow the same ) , a large pump more efficient than small pump , so from the perspective of saving a large pump rather optional , instead of two small pumps , but any of the following situations , consider two pumps in parallel cooperation : flows, a pump can not reach this traffic . 50% of the need for large pumps standby rate , can be changed in two smaller pump , two on standby ( a total of three lifting ) for some large pumps , the choice of 70% of the flow requirements of the pump parallel operation , not the standby pump , in a pump maintenance, the other lift pump still bear 70% of the production of transport . On the need for 24 hours non-stop operation of the pump , you should spare three pumps , running , a spare , a station maintenance.