From the perspective of flow rate and pressure range, screw pump design is superior to any other type of pump. The flow rate processed by the screw pump per minute ranges from a fraction of a gallon to several thousand gallons. The pressure of a screw pump depends on the number of stages (stator lead) and can generally reach 800~1000psi. Screw pumps can handle a wide range of fluid viscosities, ranging from water like fluids (1 cst) to other fluids with viscosities up to 1000000 cst of clay, cement, and sludge.
The rotor and stator of a screw pump have an interference fit (the coated metal rotor is inside the stator with an elastic lining), with low rotational speed and very low internal shear rate. When screw pumps are used in the food industry, sometimes they are used to transport cherries and apples, which are not damaged when transported through internal channels. The pulse free flow and noise free operation of screw pumps are particularly suitable for conveying materials sensitive to shear.
Screw pump is a high-quality self-priming centrifugal pump with good suction characteristics. When used to transport air and natural gas, only minimal agitation or foam is produced.
Another main feature of screw pumps is their high resistance to impurities and wear, and they are commonly referred to as the "most durable pumps.". Due to the unique characteristics and wear resistance of the elastic lining on the inner wall of the stator tube, screw pumps are often used in situations with severe wear and tear. These elastomers are made from conventional rubber (sodium butadiene rubber) or imported materials such as fluorinated rubber, polytetrafluoroethylene plastic, and other materials.
Although screw pumps have many uses, they also have limitations, mainly due to the size of their volume. In order to prevent the phenomenon of fluid slippage (leakage from the outlet with high pressure back to the inlet), when the pressure increases, the lead (number of stages) of the rotor/stator must be increased, which increases the total length of the device. For high pressure environments, sometimes it is difficult to improve the equipment in use, especially in areas where small pumps (such as centrifugal pumps) have been used in the past. However, when the venue is not restricted, this restriction is not a factor of constraint.
Another factor contributing to the larger size of screw pumps is their low rotational speed, which requires a gear reducer (or belt drive) between the driving device and the pump. This will lead to an increase in costs. However, the latest release of variable frequency drives (VEDs) allows for the removal of gear reduction devices, while introducing a new method of changing flow when overcoming pressure lifting.
Another limitation of screw pumps is the compatibility between the fluid being transported and the elastomer. Some chemicals may cause problems with the elastomer, while other substances may cause swelling of the elastomer. For applications in corrosive environments, fluorinated rubber or even polytetrafluoroethylene stators are chosen. Compared with all metal pumps, the rubber of screw pumps is also limited by temperature. Generally speaking, the working temperature of screw pumps is between 300 and 350F. Screw pumps cannot run dry unless the time is short, otherwise heat is generated at the contact surface between the rotor and stator, which may cause the rubber of the screw pump to fail, commonly known as rubber aging or debonding.