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November 17, 2021

An Overview of Rotary Pumps

By claresnape

Large Water pumps with electric motors

Rotary pumps are vital pieces of equipment for many industrial plants, especially those working with high viscosity fluids such as motor oil. Understanding how rotary pumps work is important when selecting the correct type of pump for your plant’s needs and ensuring it functions correctly.

What is a rotary pump?

A rotary pump is a versatile pump that uses an internal mechanism to push fluid from one point to another. There are two main categories of rotary pumps: single rotor and multiple rotors. There are different types of rotary pumps categorized by their internal pumping element within these two main categories. Rotary pumps can be used with many types of fluids, including high viscosity fluids, setting them apart from other pumps. Relatively small, these pumps are incredibly efficient and provide a consistent output flow, regardless of input pressure.

How do rotary pumps work?

Rotary pumps consist of an input point, the pumping element (lobes, screws, gears, or vanes), and an output point. Fluid enters the pump through the input point. Once the fluid has entered the pump, the rotation of the pumping element creates pressure which then pushes the fluid through the output point at a consistent flow rate.

Types of rotary pumps

Rotary pumps are categorized by their internal pumping elements, and since different needs are best suited to specific pumping elements, it is crucial to choose the correct element. Some of the main types include:

  • Rotary Vane Pump: These pumps use suction to draw fluid into the pump. The vanes move in and out while the rotor spins, trapping the liquid and carrying it to the output point. The contraction of the space pushes the liquid out of the pump through the output point. Rotary vane pumps work well with lighter viscous liquids and are used in lube oil service and tank stripping.
  • Gear Pump: The gear pump uses two spur gears that mesh together and rotate in opposite directions. As the gears turn and some of the teeth unmesh, they create suction that pulls fluid into the pump. The liquid is carried by the gear teeth and forced through the output point when the gear teeth mesh together again.
  • Screw Pump: There are many types of screw pumps characterized by the number and pitch of screws. While some of the specifics may vary based on the number of screws in the pump, screw pumps carry liquid through the rotation of the screws. As the screws turn, the liquid is pulled into the pump and is moved between the screw threads. The fluid is expelled through the center of the screw pump. Screw pumps are frequently used on ships to pump fuel.

Troubleshooting Tips

If you experience trouble with your rotary pump, give these tips a try to resume the regular operation of your pump. 

The pump loses its prime.

First, make sure your liquid supply has not been exhausted. If your liquid supply is still full, take a look to make sure your pump has not developed an air leak in the suction piping and that the bypass line is not heating your incoming fluid.

The pump is using too much power.

Make sure your liquid viscosity is not higher than you anticipated. A higher viscosity liquid can take more power for the pump to function. Also, check that the rotating element is not misaligned. 

The pump has a low output.

Fully functional elements are key to your rotary pump working optimally. Take a look and make sure there are no clogs, open lines, or worn-out parts. Replace any leaking elements and loose seals.

The pump is making more noise than usual.

Tighten any loose bolts and make sure the piping is properly supported. Also, ensure that the pump and driver are correctly aligned, and if they are not, make sure to realign them to prevent damage to the pumping element.

If you are still having trouble with your rotary pump or wondering about how to determine if your pump elements are properly aligned, feel free to connect with us about your questions.

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