How a 4 Lobe in 5 Lobe Pump Functions

By: Matt Hunt

Date: October 6, 2005

Definitions:• Discharge/exhaust: Exit point of fluid from the pump.• Prime: To prime a pump is to maintain or replace fluid in the pump

when the pump is not functioning.• Pump: Device used to impart energy to a fluid in order to move it

from one point to another.• Rotary Pump: Pumps which consist of a closed casing in which

gears, lobes, vanes, or screws rotate with a minimum of clearance. These rotating parts trap the liquid and push it around the casing from suction to discharge.

• Suction: Entry point of fluid into the pump.• Vanes: Are a mechanism used to optimize the seal of the pump.

They are mechanically held in their slots, and to some extent, free to move outward. Centrifugal force keeps the vanes snug against the chamber and the other rotating members

How it works• The four lobe in five lobe pump has a central rotor with 4 lobes.

These four lobes act as gear teeth that are form fitting to an outer rotor with five inner lobes. These two rotors are offset yet form fitting. The offset is to trap fluid and force it from the suction (or entry) and push it to the discharge (or exhaust). The lobes are form fitting to ensure that there is no back feed (no fluid comes out the suction or in through the discharge).

• Most rotary pumps must be primed. If they do not have the fluid that is to be pumped in them they will be full of air. This results in the pump not working as the air flow will not create enough pressure to move the less viscous fluid. This can easily be avoided with the use of valves. The type of valve is dependent on operating pressure (high or low) and the properties of the fluid being handled such as viscosity, temperature, clear or containing suspended solids.

Advantages:

• Consistent flow of fluid resulting in continuous pressure versus surges of pressure

• Pass medium solids

• -Easy to maintain and clean, good for the food industry

• Less friction (than reciprocating pump) resulting in longer lifespan

Disadvantages:

• Reduced lift on low viscosity liquids

• Cannot handle high pressure

• Must have a relief valve on the discharge side of the pump

• Must be primed to function

References

• http://www.tpub.com/content/engine/14105/css/14105_53.htm

• http://www.pumpschool.com/principles/lobe.htm

• South Alberta Institute of Technology. Correspondence Courses Power Engineering, Section 3 Third Class Lecture six. Pumps. Calgary Alberta.