A gear pump is a type of metering pump
Metering pumps can be considered a subset of positive displacement pumps. Both pumps discharge a known volume with every revolution or cycle. The discharge volume is largely independent of back pressure. What differentiates metering pumps from positive displacement pumps is their accuracy. Metering pumps have an average accuracy of ± 1.0 percent.
There are several metering pump categories, including diaphragm, piston, gear and peristaltic, that feature a fixed-volume cavity to deliver the same volume with every pumping cycle. Therefore, the challenge with any metering pump design is to control cavity dimensions and minimize leaks and dead volumes. This blog post will focus on the gear pump.
How gear pumps work
Gear pumps work by trapping fluid between the teeth of two or three rotating gears. Often, they are magnetically driven, which means they use less “wetted” materials for greater chemical compatibility. Gear pumps move a cavity that rotates rather than reciprocates. These pumps move many small cavities per revolution, so they do not pulse nearly as often as diaphragm pumps. The major disadvantage of gear pumps is that increasing the backpressure does decrease the flow rate. They work best when pumping against stable backpressure. Since gear pumps operate by carrying fluid between the teeth of two or three rotating gears, they are best suited for applications in which fluid shearing or particle contamination from gear wear is not a concern.
The following video will give you an overview of how a gear pump works.
These pumps operate well with high system pressure applications and are commonly used for hydraulic fluid power uses, for example in tractors and garbage trucks, and with heavier viscosity fluids, such as oil, that are not compressible.
Gear pumps feature true positive displacement with every revolution delivering a precise volume. Since each pocket of fluid that passes through the chamber is small and so many pockets go through per unit time, the flow rate is virtually pulseless.
With metering, circulation, dosing, and transfer capabilities, gear pumps are efficient in offering a fast response, continuous flow, and dose accuracy. Analytical chemists use gear pumps for dissolution testing, liquid handling, sample dilution, and flash chromatography. The pumps handle fluids in diverse industries from dispensing spray wax coatings onto foods to metering flavors and fragrances to adding optical brighteners to paper. They are found in chemical processing, laboratories, pharmaceuticals, industrial facilities, energy and fuels, and paint and ink production.
Gear pumps vs peristaltic pumps
While peristaltic pumps offer many advantages, a gear pump is sometimes a better choice than a peristaltic pump. Gear pumps deliver a wider range of flow capabilities than peristaltic pumps and a slightly wider range than hose pumps. Because gear pumps can use more rigid tubing as the solutions enter and exit the pump, there is little to no absorption of fluid. Conversely, peristaltic pumps operate with more flexible tubing allowing for some fluid absorption and fluid fluctuations.
See the comparison chart below:
|Gear pumps||Peristaltic pumps|
|Positive displacement||Fixed volumes due to rigid components||May vary due to age of tubing|
|Pressure capabilities||Higher back pressures||Lower pressure capabilities; better suction|
|Temperature range||Wide||Varied range, but not as wide|
|Pulsation||Less* (near pulseless)||More|
|Particulates||Does not handle particulates||Handles particulates|
|Viscosity||Handles fluids with lower viscosities||Handles higher viscous fluids|
*Compared to most peristaltic pumps. Large-hose peristaltic pumps are the exception
Maintenance for gear pumps is more time-consuming than peristaltic pumps, as users must open up the pump to clean its gears and the pump head. Also, gear pumps may be limited in terms of chemical compatibility, with pump materials typically crafted of stainless steel, PTFE, or PEEK. Finally, particulates are messy within a gear pump and the pump does not tolerate them well. In this instance, a peristaltic pump may be the better option.
When an application calls for pumping a clean fluid without particulates in a consistent flow, a gear pump is often the best pump to use. For example, in industrial applications such as pumping inks, coatings, or for pipeline injection, a gear pump would be the recommended solution.
Cavity-style vs. suction-shoe design
Gear pumps consist of the drive and pump head. Most commonly the drives are combined with the following two options of attached gear pump heads.
The cavity-style is designed to handle higher inlet pressures. They employ two or more rotating gears that mesh together and depend on the surrounding fluid pressure in the magnetic cup to maintain a tight seal between the gear teeth. This pump head is best for applications requiring suction lift, frequent cycling, or a pressured inlet.
The suction-shoe design gives higher delivery pressures and superior priming performance. These pressure-loaded pump heads have a suction shoe positioned around the inlet. Higher pressure in the magnetic cup relative to the inlet side holds the gears and suction shoe tightly together. This design increases volumetric accuracy by ensuring complete fluid transfer with no backflow or leakage between gear tips, even at elevated pressures. Since the pump efficiency increases as discharge pressure increases, these pump heads work well with applications requiring high initial differential pressures and precise flow rates.
The best pump for the job?
Gear pumps are the optimal choice when seeking hydraulic and power efficiency, corrosion- and abrasion-resistance, a pulseless continuous flow with no dynamic seals, and a fast response. Because they can run for long periods between maintenance, they are suitable for continuous duty applications, such as filling and dispensing operations requiring a pulseless flow and general transfer and sample delivery.
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