In fluid transport systems,the rotary pump serves as the power source for the entire system.Head,being one of the core parameters for pump selection,directly relates to the stability and economy of system operation.In practice,many engineers misunderstand head,simply equating it to the delivery height,which leads to selection errors and a series of problems.

Comprehensive Understanding of Head Components

A complete head calculation should systematically consider the following five aspects:

Total pipeline system resistance loss,including frictional losses along the pipe and local resistance from fittings;

Pressure drop loss through process equipment,such as the pressure consumed by specialized equipment like heat exchangers and filters;

The vertical lift height of the material delivery,i.e.,the potential energy difference between the inlet and outlet;

The minimum inlet pressure required by the operation of the end-user equipment,ensuring the normal operation of subsequent processes;

A safety margin in the engineering design to cope with system fluctuations and performance degradation over long-term operation.

These five elements are indispensable and together form the foundation for accurate selection.

Calculation Methodology for Hydraulic Losses

The Hazen-Williams formula is recommended for calculating the frictional head loss.This formula adapts to various pipe materials by adjusting the pipe roughness coefficient.For example,plastic pipes use a coefficient of 150,new stainless steel pipes use 130,while old cast iron pipes decrease gradually to 75-90 with years of use,fully considering the impact of pipe wall roughness on flow.

The local head loss is calculated using the resistance coefficient method.This involves summing the resistance coefficients of valves,elbows,reducers,and other fittings,and combining them with the pipeline flow velocity for calculation.Engineering practice requires consulting authoritative design manuals to obtain the precise resistance characteristics of different pipe fittings.

Case Study Analysis

A chemical process uses a rotary pump to transport process liquid.The design flow rate is 40 m³/h,the delivery pipeline is DN100 new carbon steel pipe with a length of 80 meters.The system includes a heat exchanger(pressure drop 3 m),a vertical lift of 6 meters,and the end reactor requires an inlet pressure of 0.15 MPa.The pipeline configuration includes 1 concentric reducer,1 check valve,2 gate valves,and 6 90°elbows.

Calculation Process:

1.Pipeline frictional head loss:Substituting into the Hazen-Williams formula,using Ch=120 for carbon steel pipe,calculates hy=3.2 m.

2.Summary of local resistances:The sum of the resistance coefficients for various pipe fittings∑ε=9.8,calculates hj=1.4 m.

3.Total system required head=3.2+1.4+3+6+15=28.6 m.(Note:0.15 MPa≈15 m head)

4.Considering a 10%safety margin,the final selected head is 31.5 m.

Practical Suggestions

Head calculation must be closely integrated with process characteristics,fully considering performance changes after long-term system operation.It is recommended to reserve an 8%–12%margin based on the calculated value.This can both cope with unexpected conditions and avoid energy waste caused by over-design.For complex systems,it is advisable to use professional hydraulic calculation software for verification.

Bonve always adheres to the philosophy of "Wholeheartedly Making Good Rotor Pumps," committed to providing global customers with customized conveying and mixing solutions. If you have technical inquiries, selection needs, case references, or other cooperation intentions related to Bonve rotor pumps, please feel free to contact us.  

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