26 May Uses of Spindle Pumps
What Are Spindle Pumps and What Are They Used For?
When reviewing the long history of mankind’s efforts to draw water from its source for use elsewhere, the first mechanical means of doing so is generally attributed to Archimedes. However, the true inventor appears to have been an Egyptian and may have preceded the Greek mathematician, astronomer, and engineer by as much as a century. Still widely referred to as an Archimedes Screw, it consisted of a rotating spiral structure which fitted tightly inside a cylinder. A distant predecessor of modern spindle pumps, it employed much the same principle. Turning the screw-like insert caused water to be drawn into the cylinder and raised further with each subsequent rotation. In fact, these more compact modern counterparts of the primitive device are often referred to by the more descriptive title of screw pumps.
These devices depend upon the principle known as positive displacement, in which the contained fluid is moved by repeatedly displacing the space that it occupies. The faster their screws rotate, the greater the flow rate. One of the possible drawbacks of spindle pumps is that, in order for the screw to rotate freely within its housing, there needs to be a small gap between the two. This means that the Archimedes Screw, though sufficiently effective and still used in some places today, does tend to allow water to pass backwards through that small gap. The same tendency persists in the modern equivalent but does not significantly affect its performance. Nevertheless, because of this trend, the design of these devices calls for extremely tight clearances.
Not surprisingly then, one of the main applications for modern spindle pumps is to transport viscous fluids such as oil. In this case, the transported fluid itself acts as a built-in lubricant. This allows the clearance between the impeller and the housing to be machined to a more precise fit without slowing its rotation which would, otherwise, lead to a reduction of the flow rate. The process is not only used within the oil industry, where it works equally well despite the presence of pockets of gas, but can also serve as a means to generate the hydraulic pressure to perform work or to circulate coolant. Because their action is purely rotary, spindle pumps are able to run more silently than most other varieties. This makes them a good option for operating a water- or oil-based cooling system. Also, because increases in pressure have very little effect on their performance, they are an equally good choice for use in high-G-force applications where it is essential to ensure that the fluid pressure and flow rate remain constant.
One example of a device that depends for its operation on both of these applications is the CT scanner. Both the hydraulic control of its rotating gantry system and its critical cooling system rely on the action of these spindle or screw pumps. They are well-suited to these tasks due to their long-term reliability. This ensures that these medical imaging systems will be far less affected by frictional wear and tear on bearings, impeller blades, and seals than if they were to depend on most other types of pump. Not all their uses are quite as exotic, however. When orientated vertically, one of the day-to-day but no less important tasks for spindle pumps is to improve the pressure and flow rate of the water supply to the upper floors of a building. Once again, it is the combination of comparatively silent running, consistent performance, and durability that has served to make these devices a practical choice for this type of application.
When it comes to the selection of pumping equipment, the chemical industry poses its own challenges. Many of the liquids that are to be transported are highly corrosive and can quickly damage seals and any unsuitable materials used in their construction. To counter this problem, Prochem manufactures a range of seal-less vertical spindle pumps in which all the components that come onto contact with the fluid are made from a synthetic resin that is highly resistant to both corrosion and abrasion. Not only are thermosetting resins substantially cheaper than stainless steel or exotic alloys such as Hastelloy and titanium, but they are also resistant to a much wider range of chemicals. Prochem’s resin-based vertical spindle pumps can be safely used for liquids at temperatures ranging from -200 to +120 °C and are also much quieter and less prone to vibration than metal pumps.