A rotary lobe pump is a positive displacement pump that uses two or more cams to move liquids by rotating them around parallel shafts in the pump body. They are widely used in hygienic processing industries, including food and beverage processing and biopharmaceutical manufacturing.

Below I will describe the rotary lobe pump in detail:

Their uses:

How they work

How to make the most of their performance

Unlike gear pumps, the lobes used in these pumps do not physically contact each other, a feature that provides some distinct advantages when pumping certain types of materials. During operation, the shaft connected to the impeller rotates in the opposite direction, repeatedly creating low pressure within the pump body, and the suction product moves from the inlet port of the pump around the outside of the impeller of the pump to the outlet port.

Since the movement of the pump blades causes the pump to discharge a specific amount of fluid with each rotation, the output of the pump can be easily controlled by mechanically changing the speed of the pump motor, typically using a variable frequency drive (VFD).

Advantages of rotary lobe pumps:

Since the leaflets of the pump do not touch each other, the leaflet pump can move solids suspended in the slurry, such as cherries or olives in food processing applications, without damaging the product.

Gentle pump action further reduces product damage.

Larger size particles can be handled than pumped by other types of positive displacement pumps.

It can be easily cleaned using clean-in-place (CIP) or steam-in-place (SIP) methods, making it ideal for hygienic processing applications.

Very efficient pumping of very viscous liquids.

Sufficient fluid viscosity is assumed to provide accurate and consistent fluid output that is not affected by changes in head pressure.

The fluid flow can be increased or decreased by controlling the drive speed.

If wetted, the rotary lobe pump is also self-priming and can run dry for long periods of time (assuming the pump's seals are lubricated).

Generally easy to maintain.

Disadvantages of rotary lobe pumps

The purchase price of a lobe pump is usually higher than that of other positive displacement pumps, taking into account the specific application

Since they are driven by a motor and gear reducer (which affects the speed and output of the pump), the rotary lobe pumps have a relatively large footprint, which may have been a factor in the installation.

The two sets of mechanical seals used in lobe pumps increase maintenance and total cost of ownership.

The design of lobe pumps requires the use of pressure relief valves and safety bypass valves, which adds to their complexity.

When pumping low-viscosity fluids, the efficiency of the lobe pump suffers.

Get the most out of your rotary lobe pump

The rotary lobe pump delivers a limited volume of fluid for each operating cycle, i.e., each revolution of the cam. Aside from slippage, the only factor that determines the amount of fluid pumped is the speed at which the blades rotate (i.e., the speed at which the pump is running, not the RPM of the motor). Most lobe pumps use a gearbox to increase or decrease the operating speed.

To calculate the amount of fluid pumped at a given speed, pump engineers generally use what is known as a pump curve. These engineering calculations are often used to determine the performance of positive displacement pumps with different types of fluids and different operating parameters.

Two variables are typically plotted on the pump curve: pump speed in RPM s and pump output in GPM. In the example illustration, multiple lines are drawn. This is to explain the so-called slippage, a phenomenon that occurs in positive displacement pumps under different operating parameters. Slip is the amount of fluid flowing from the discharge side of the pump back to the suction side of the pump during normal operation. In other words, slip is the amount of fluid that recirculates through the pump body while the pump is running, not the amount of fluid that is pumped out of the pump outlet. The amount of slippage of a rotary lobe pump is determined by two factors, the viscosity of the pumped fluid and the differential pressure of the pump. For the first point, as the viscosity of the fluid increases, the amount of slippage decreases because the more viscous fluid cannot slide back into the gap in the pump blade flap as easily as the diluted fluid. Then, as the discharge pressure of the pump increases, so does the slip as the pump works harder to move the fluid from the suction side of the pump to the discharge side and out. It's kind of intuitive, because the pressure increases, so it slips. Due to slippage, most rotary lobe pump manufacturers draw multiple lines on the pump curve to show the effect of slip on fluids of various viscosities and under different pump operating conditions. In simple terms, pump curves are used to determine the output of a rotary lobe pump. They help determine the size of the pump required to achieve a specific output. There is a saying in the pump world that "displacement determines the pump, and pressure determines the motor." "This curve can be used to determine the required power (i.e., required horsepower), taking into account the viscosity of the fluid being pumped, the slip factor, and the discharge pressure of the pump.