The Quick Guide to Internal Gear Pumps

With the wide variety of pumps available today, it’s sometimes hard to know which is best for your specific application. Which can handle the viscosity of the fluid? Generate the proper flow and pressure? 

To be certain the proper pump is applied, it’s a good idea to consult an engineer well-versed in pumps. However, this post should prepare you for that conversation and provide a good understanding of the inner workings and characteristics of internal gear pumps so you can determine if they are a good fit for the application.

INTERNAL GEAR PUMP OVERVIEW

Internal gear pumps are positive displacement pumps. They are very versatile, with the ability to pump many different types of fluids at a wide range of viscosities and temperatures. An internal gear pump operates using two rotating gears to move fluid. A rotor gear on the outside and a smaller, idler gear nested inside.

HOW INTERNAL GEAR PUMPS WORK

As the rotor (outer) gear turns, it drives the idler (inner) gear. When the idler gear comes out of contact with the rotor gear, a low-pressure zone is created. The liquid is drawn into the pump and travels along with the casing to the discharge side of the pump. The gear teeth mesh back together and force the fluid out of the pump.

Proper gear clearance is essential to the long life and efficiency of these pumps. If the clearance is too wide, pump efficiency will suffer. If pump clearance is too tight, as in the case of thermal expansion, the gears will make contact and cause damage or failure. 

Unlike a centrifugal pump that cavitates against blocked discharge lines, an internal gear pump will continue to generate flow and build pressure. The pressure will continue to build until something releases it. Oftentimes, this results in a pump failure and a costly component repair or replacement.

Internal gear pumps are oftentimes equipped with an internal or external relief valve. This valve diverts flow when pressure builds in the discharge line, preventing catastrophic failure.

BEST APPLICATIONS FOR INTERNAL GEAR PUMPS

Internal gear pumps are ideal for high viscosity fluids. This is just a short list of applications where internal gear pumps can be used.

• Food products (corn syrup, oils, nut butter, chocolate)
• Dairy products
• Personal care products (pastes, creams, soaps)
• Wide range of oils and lubricants
• Paints, pigments, ink

They’re also great for situations where low NPSH is required. With only two moving parts, they’re also pretty low maintenance.

WHAT THEY’RE NOT SO GREAT FOR

Internal gear pumps do not do well with large solids. Because they’re made with small tolerances, large solids can easily damage the pump. They can handle some small suspended solids in abrasive fluids but be advised that this can cause the pump to wear and lose performance.

Internal gear pumps can become less efficient as fluid viscosity decreases. 

In situations where the product viscosity is low, and discharge pressure is high, the product can “slip” through machined clearances in the pump, causing it to recirculate from the discharge side to the suction side. You can read more about slip in a previous post, What is a Suckback on a Gear Pump?

In most cases, product slip is an annoyance and an issue for efficiency but can cause bigger problems with certain products that harden when at rest such as chocolate and adhesives. 

IN CONCLUSION

Internal gear pumps are one of the most versatile positive displacement pumps available. There is also a myriad of options to consider from pump size to product temperature. Make sure the right pump is applied by talking to an experienced engineer before purchasing. 

If you need help selecting the right pump for your application, ask us about it! We gladly provide technical assistance to businesses in Wisconsin and Upper Michigan.