Does your rotary lobe pump stop you pumping solids or abrasives?

Rotary lobe pumps are common in the manufacturing industry as a gentile, self-priming pump solution to handle a wide range of viscosities. These pumps, however, have limited compatibility with fluids and are extremely vulnerable because of their complex design, which can lead to hazardous situations and unusually high maintenance costs. Graco’s QUANTM electric operated double diaphragm (EODD) pumps address these common issues.

Rotary lobe pumps

Rotary lobe pumps are used in a wide variety of industries and applications, because of their relatively small footprint and their ability to withstand high temperature. However, they suffer from some significant disadvantages that can lead to frustrating downtime, expensive repairs, and even product replacement.

• Reduced lift with thin liquids
  Extra care is needed when selecting a rotary lobe pump for pumping thin non-lubricating liquids. All pumps have a small amount of liquid that goes from discharge back to suction. This is called slip, and it varies with liquid viscosity and differential pressure. Some rotary lobe pumps can be used with thin liquids, and most manufacturers offer several options to handle the low lubricity and viscosity typically associated with thin liquids, but it adds more complexity to the pump selection procedure and maintenance processes after installation compared to using EODD pumps.

• High maintenance cost
  Rotary lobe pumps are comprised of a number of rotating parts that need precision tolerances, which makes them more expensive to manufacture and maintain. Additionally, the rotating parts utilize expensive and sensitive seals that can easily lead to leaks if the pump is pushed beyond its performance and not properly cleaned or maintained over the service intervals.

• Investment costs
  Rotary lobe pumps are designed with rotors, which are synced by a separate gear in the back of the pump. This increases manufacturing cost. Add to this the two relatively expensive mechanical seals and, not surprisingly, investment costs are relatively high in comparison with other pump technologies on the market. This high cost is on the front end and over the life of the pump, especially if they are not monitored in their applications. 

• Unsatisfactory solution for abrasives
  The rotary lobe pump’s intricate and sensitive design is not ideal for abrasives, which are bound to damage the system and its expensive parts. The pump’s lifecycle can be slightly extended by reducing pump speed and using hard parts in key wear areas, but EODD pumps are clearly a better fit when you need higher flow and long lasting durability.

• Unable to run dry for extended periods of time
  A rotary lobe pump cannot run dry indefinitely without destroying its expensive stators and rotors. The pumped fluid acts as a lubricator between rotor and stator.