In the field of industrial fluid transportation,medium viscosity is one of the core parameters that determine the operating status of pump equipment.Media with different viscosities have significantly different flow characteristics in the pump cavity,which will directly change various operating indicators of the equipment and even affect the stability and service life of the system.

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When the rotational speed remains constant,an increase in medium viscosity will generally reduce the flow rate,head and efficiency of the pump,but the shut-off head always remains unchanged.This is because the increase in viscosity will aggravate the internal friction losses inside the pump,and the actual output head will decrease at the same flow rate.Moreover,the larger the flow rate,the more obvious the drop in head.The shut-off point corresponds to the working condition with zero flow rate.At this time,the impeller head calculation formula is H_shut−off=u₂²/g(1+p),which is independent of the medium viscosity.Therefore,the head curve after viscosity correction will coincide with the clean water working condition curve at zero flow rate.For some closed impeller low specific speed pumps,when the viscosity increases slightly,the influence of impeller ring leakage will be reduced,and the head may be slightly higher than that under clean water conditions.Only when the viscosity increases further will the head start to decrease.

When the viscosity increases,although both the flow rate and head decrease,the rate of efficiency decline is much faster than the reduction rate of the product of flow rate and head,which will eventually lead to an overall increase in the shaft power of the rotary pump.The shaft power of a rotary pump can be divided into three parts,and the calculation formula is  P_shaft=ρgQH/ηVηh+P_B+P_A are the volumetric efficiency and hydraulic efficiency respectively,P_B is the disc friction loss,and P_A is the mechanical loss.The first two terms are significantly affected by viscosity,while the third term is independent of viscosity.The increase in viscosity will not only increase friction and hydraulic losses to push up the shaft power,but also reduce leakage losses to improve efficiency.At the same time,the heat generated by friction will reduce the medium viscosity and weaken its influence.In general,the increase in viscosity will increase the shaft power,and the increase may exceed the calculated value of the conventional correction coefficient.Therefore,for motor power selection,you must verify the actual value with the pump manufacturer.

The influence of viscosity on the required net positive suction head(NPSHr)has a dual nature:on the one hand,the increase in viscosity will increase the pressure drop from the pump inlet to the lowest point of the blade,leading to an increase in NPSHr;on the other hand,viscosity will inhibit the expansion of bubbles in the pump and reduce the impact of cavitation on the external characteristics of the pump.

The increase in medium viscosity will also significantly increase the starting static torque,thereby increasing the starting torque and starting current required by the motor.Especially for equipment such as hot oil pumps,the medium viscosity during cold start is much higher than that at normal operating temperature.At this time,it is necessary to verify whether the starting torque and current multiple of the motor meet the requirements,and a soft start device should be configured if necessary.

Therefore,medium viscosity has an extensive and complex impact on the operating performance of pumps.In equipment selection,system design and daily operation and maintenance,the viscosity factor must be fully considered,and accurate calculation must be carried out in combination with actual working condition parameters to ensure the safe and efficient operation of the conveying system.

Bonve pump 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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