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# Flow control of centrifugal water pump

How to economically and effectively control the pump output flow once triggered a major discussion, once popular all use frequency control to control the output flow, the elimination of all control valves to control the flow of the type, from the current point of view alone, there are four widely used methods on the market: export valve opening adjustment, bypass valve adjustment, adjust the impeller diameter, speed control. Now let’s analyze and discuss the characteristics of each method one by one.
Common control methods for centrifugal water pump flow.

In this method, the pump is connected in series with the export pipeline regulating valve, its actual effect is like using a new pump system, the maximum output pressure head of the pump has not changed, but the flow curve has decayed.

In this method, the valve and the pump are connected in parallel, and its actual effect is like the adoption of a new pump system, the maximum output head of the pump has changed, while the flow curve characteristics have also changed, the flow curve is closer to the line.

This method does not use any external components, the flow characteristics curve changes with the diameter.

## Speed control

Impeller speed change directly changes the flow curve of the pump, the characteristics of the curve does not change, when the speed is reduced, the curve becomes flat, the pressure head and the maximum flow rate are reduced.
1) The overall efficiency of the pump system
Outlet valve adjustment and bypass adjustment methods both increase the pipeline pressure loss, and the pump system efficiency are significantly reduced. Impeller diameter adjustment has less effect on the overall pump system efficiency, and the speed control method basically does not affect the system efficiency, as long as the speed is not less than 50% of the normal speed.
2) Energy consumption level
Assuming that the output flow rate of the pump is adjusted from 60m3/h to 50m3/h by the above four methods, and the power consumption is 100% when the output is 60m3/h (at this time the pressure head is 70m), how do several methods of controlling the flow rate affect the power consumed by the pump?

• (1) Outlet valve opening adjustment, energy consumption is 94%, the power consumption is larger when the flow rate is lower.
• (2) Bypass adjustment, the bypass valve reduces the pump pressure head to 55M, which can only be achieved by increasing the flow rate of the pump, resulting in a 10% increase in energy consumption.
• (3) Adjust the impeller diameter, reduce the diameter of the impeller pump output flow and pressure are reduced, energy consumption shrunk to 67%.
• (4) Speed control, speed reduction, pump flow and pressure head are reduced, energy consumption shrunk to 65%.
• Summary of centrifugal pump flow control methods.

The following table summarizes the various methods of flow regulation, each method has its own advantages and disadvantages, and should be selected according to the actual situation.

 Flow regulation method Continuous regulation Change of flow characteristic curve of pump Efficiency change of pump system When the flow decreases by 20%, the power consumption of the pump Outlet valve opening adjustment Ok The maximum flow decreases, the total head remains unchanged, and the flow characteristics change slightly Significantly reduced 94% Bypass valve regulation Ok When the total head decreases, the curve characteristics change Significantly reduced 110% Adjust impeller diameter No The maximum flow rate and head decrease, and the flow characteristics remain unchanged Slight decrease 67% Speed control Ok The maximum flow rate and head decrease, and the flow characteristics remain unchanged Slight decrease 65

Source: Network Arrangement –  – Yaang Pipe Industry (www.epowermetals.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)