in Diaphragm Pumps

How Viscosity affects pump performance

Fluimac logo air diaphragm pumps

Many customers use pneumatic diaphragm pumps for general pumping applications.

The pumps are often mounted onto a base plate and carried in the back of a truck or trailer to be used to dewater trenches or to extract oils from oil traps etc.

Every once in awhile we will have a very confused customer who normally pumps a water effluent from a sump at 100 litres per minute with a 1″ pump.

However, when his pump unit needs to pump a thicker fluid like a heavy gear oil this same unit will only produce a flow of 60 litres per minute?

Viscosity reduces the capability of the air diaphragm pump’s performance. 

The diaphragm pump will deliver progressively less of a % of its low viscosity rated flow, normally based on water in the performance curve.

As the viscosity elevates the % of flow the pump is capable of delivering reduces as per the indicated curve above.

While the curve we have generated is not conclusive it is a fair estimation of the degree of losses in terms of pump flow capability as the viscosity increases.

For more accurate assistance with your application please do not hesitate to call +27 31 777 1629 or email