Screw PumpsWhat is a screw pump?A screw pump is a modification of a helical gear pump. The term however is used generically as it fails to incorporate the uses and design consideration of each sub screw configuration, making each design highly suitable for specific applications (most are custom made).Working PrincipleHowever, despite the large variety in terms of design and application.Each Screw pump operations on the principle that a screw turning would isolate a volume of fluid and convey it and/or compress the said fluid.Compression is achieved by either slowly reducing the volume chamber (or dams) as the fluid progresses through the cavity, and thus object the fluid to a higher amount of pressure.Conveying the fluid as is the case of the Archimedean Screw is that the pumping element simply traps a particular volume of fluid and conveys it from one plac to anotherDesign Configurations single screw/eccentric screw/ progressive cavity pumps,, external bearing, timed twin screw pumps, internal bearing, product lubricated twin screw pumps, three screw pumps with internal bearings, three screw pumps with external bearings, single suction designs, double suction designs, multiple screw designs Archimedes Flood Control Pump

Single Screw Pumps-contains a single pumping element which rotates within a stator.Stator-the protrusion that make up the lining of the volume or housing encasing the pumping elementThe said stator has a shape that corresponds to the shape of the pumping element. Some designs of the stator may be elastomeric others solid.The pumping element is only supported via a universal joint on one end, giving the single pump its eccentric movementHowever since the pumping element is continuously in contact with the stator, given that screw pumps usually operate via a large amount of angular velocity, there is a need to cool the stator every now and then to avoid extensive wearing.Two Screw PumpsTypically, the said term is applicable to a screw pump with two pumping elements and two shafts, additionally the two screw pump may be considered as a four screw pump if it is a double suction design.For this handout, the two-screw pump is considered as a single suction type. The pumping elements comprise of two intermeshing screws rotating within a figure 8 type housing. In this particular design, the two pumping elements are supported on both sides unlike the single screw pump.Here, the two pumping elements are well timed such that that there is no metal-to-metal contact, where one rotor turns one pumping element and which now turn the second pumping element.Additionally, in this design type there is no elastomeric stators lining the housing, instead there is only sufficient clearance between the pumping elements and the housing. Which allows for more aggressive handling of fluids.

Example of a Single Suction, Two Screw pump.Three Screw PumpsA three-screw pump operates on the same principle of intermeshing pumping elements as the previously discussed two-screw pump.Generally, the three-screw pump utilizes a centrally rotating pumping element (supported at both ends), which in turn rotates the two secondary screws/idler rotors (only supported on one end), which are, then located 180 degrees from each other (the axes of the pumping elements are perpendicularly inline)For this handout, the two-screw pump is considered as a double suction type.

During operation, this type of pump allows the pumping element to create a thin film of fluid around it, which then stabilizes the pumping elements inside. This however limits the fluids to non-galling, low viscosity of fluids. Potential disruptions of the fluid film can cause the rotor to lose support and meet each other, locking the screws and stopping the pump operation (potentially damaging internals).Three screw pumps are ideal for clean, lubricating fluids. Fluid film thickness and operating clearance is typically smaller than that of a two-screw design, giving higher efficiencies and higher pressure capabilities than a two screw pump providing viscosity is adequate and fluid is clean enough to avoid disruptions to the internal fluid film. Example of a Double Suction, Three Screw pump.