Plastic Gears for Low-Viscosity Gear Pumps: Why They Perform Better

Many users have a preconceived notion when selecting pumps: they often believe that products like gear pumps are best equipped with metal gears. The mention of plastic gears can give an impression of a lower-end, less durable product. Here, I will briefly explain the selection of gear and bearing materials for gear pumps in low-viscosity applications.

During the operation of a gear pump, the main rotating components are the driving gear and the driven gear. They are responsible not only for transmitting torque but also for pressurizing and transporting the liquid. This requires the gear pair to possess not only good rigidity but also excellent self-lubricating properties, high dimensional accuracy, and corrosion resistance. The requirements for rigidity, dimensional accuracy, and corrosion resistance are relatively easy to understand. But why must the gear material also have good self-lubricating properties? The reason lies in the relative sliding that occurs between the tooth surfaces of the two gears during meshing. If the material has poor self-lubricating properties—such as ordinary 316 stainless steel gears—they are very prone to seizing at even moderately high speeds. Therefore, when selecting gear materials, especially for transporting low-viscosity or poorly lubricating liquids (e.g., water or certain solvents), particular attention must be paid to the self-lubricating properties of the gear material.

Here, it is important to note a key material characteristic: the PV value. This refers to the allowable pressure (P) and velocity (V) at which a material can operate while maintaining acceptable wear levels. If a material has a poor PV value, it is unsuitable for use in friction pairs, regardless of its hardness.

Our NP series micro magnetic gear pumps from Shanghai Super Fluid Co., Ltd. (Suofu) utilize specially filled and reinforced PEEK material for both the gears and bearings, manufactured using high-precision injection molding processes. This solution effectively meets the requirements for rigidity, precision, self-lubrication, and corrosion resistance within a differential pressure range of up to 20 bar, providing an excellent option for applications involving small flow rates and low-to-medium pressures.