Gear Pumps – How they Work and some Typical Uses

One may believe that pumping equipment’s sole function is to convey a liquid or gas along a pipe or drain floodwater. In practice, this is not always the case. For example, in everyday life, there are numerous instances where it is required to deliver discreet and precise volumes of liquid, often on demand. Though not the only option, gear pumps are frequently the preferred tool to perform such tasks. Like similar devices that utilise diaphragms, pistons or peristaltic action for the same purpose, these units also operate by the principle known as positive displacement. However, their ability to deliver consistent, measured doses of liquid with an accuracy of +/- 1,0% places these devices in a unique sub-class of this genre.

Gear Pumps

Based on their ability, it is common practice to refer to this type of positive displacement device as a dosing or metering pump. Another popular metering device works like a syringe, utilising a piston to draw and expel liquids. However, gear pumps operate by trapping fixed volumes of fluid between the teeth of two or three gears from which their descriptive name is derived. Surprisingly, the idea is far from new. A German engineer named Pappenheim produced one of the first and most successful devices of this kind, way back in 1636. Furthermore, his ingenious design is still in use today.

How do Gear Pumps Work?

These units are available in two distinctly different designs. Namely, external or helical and internal or eccentric. The relative suitability of these two varieties of gear pumps for any given task will depend on factors such as fluid viscosity, temperature and various required operating parameters. There is a chance that some fluids could solidify at low temperatures. It is often possible to fit the unit with a heating jacket. Let’s take a closer look at how these two types work.

External (Helical)

Two gear wheels are mounted on separate shafts and interlock in this type. A motor drives one shaft, causing the other to rotate in the opposite direction as the teeth engage. The effect is to trap water between the teeth of helical gear pumps as it enters the inlet side, carrying it forward before discharging it at the outlet side. External models are less noisy than the eccentric type. They are the best choice for pumping thin fluids at low speed and in applications where high operating pressures are necessary.

Internal (Eccentric) 

In this design, a small gear wheel is located eccentrically within a second, larger one, allowing their teeth to engage. The eccentric wheel is mounted on a motorised shaft. By contrast, in these units, the rotary action of the motorised wheel in these gear pumps causes the outer wheel to rotate in the same direction. A crescent-shaped former between the cogs ensures the teeth of both cogwheels can effectively propel incoming fluids towards the outlet. They are a better option when handling highly viscous liquids, such as paint, polymers, resins and lubricating oils.

Regardless of the basic design, performance is also influenced by the size and shape of the gear teeth. The internal models only use spurs with relatively large gaps, which accounts for their ability to cope so effectively with those highly viscous liquids.

That said, external gear pumps depend on the gaps between their teeth to ensure their exceptional precision. Spurs, lobed, and herringbone designs are some of the standard options. However, custom-designed teeth are often required when performing more specialised tasks. In each case, a tight fit is necessary to achieve maximum precision. That close fit is also why helical models cannot handle high viscosity liquids.

For What are Gear Pumps Used?

These devices are widely used in various industries, often forming part of a production line for bottling some form of liquid. For example, gear pumps are a convenient means to repeatedly dispense 500-millilitre quantities of mayonnaise or tomato sauce into the appropriate jars. The petrochemical industry also favours the eccentric design for handling lubricating oils. Also, smaller versions are used to circulate lubricating oil in vehicles and other machinery. In eater treatment plants, chemicals such as flocculants, pH adjusters and disinfectants are also metered in this fashion.

Consistent and accurate performance is essential, whatever the application or the fluid involved. Prochem is known for world-class pumping equipment, including high-precision gear pumps for most common applications.

Sources:

URL https://appliedpumps.co.uk/what-are-gear-pumps-used-for/

URL https://www.coleparmer.com/blog/2019/02/19/how-gear-pumps-work/

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