Progressive cavity and peristaltic pumps are used in many industries. Part One of this two-part series discusses progressive cavity pump selection, mechanical seal maintenance, how spiral stator technology can improve the performance of these pumps and how the increase in hydraulic efficiency means less maintenance and a longer service life. Part Two will cover why peristaltic pumps are a good choice in many industries for ease of maintenance and long life. Progressive cavity pumps are used in several processes within the paper industry—such as pumping calcium carbonate, clays, titanium dioxide, and many chemicals. They also appeal to other industries—including oil and gas, mining and chemical. They are cost-effective, generate significant pressure and produce high flow rates.
Because these pumps require regular attention, end users should carefully consider the design options.
05/16/2014
A progressive cavity pump with even-wall spiral stator technology and a 2/3-elliptical stator and rotor
These pumps require regular maintenance. The seven-year operating maintenance costs make the initial pump investment cost seem small. If end users choose the smaller pump and the high-speed option, they will likely increase their consumption of spare parts by as much as 50 percent. Therefore, during the seven-year operating span of a typical pump, the maintenance costs could be double the costs of selecting the properly-sized pump.
End users are conscious of capital investment costs, but the desire to get the order completed and a manufacturer’s desire to optimize capital investments are, at times, in conflict with selecting the longest-lasting pump with the least maintenance costs. Pump selection is one situation in which the more expensive option may be a better investment. With time, that decision may be the most beneficial and cost-effective for end users.
Image 1. The spiral stator (left) allows for higher pressure per stage, and the 2/3-elliptical lobe and rotor generate a higher flow rate than the standard, round stator (right).
Spiral technology often offers higher efficiency and higher pressure and flow capabilities. This technology’s stator has a much thinner rubber lining. A standard round stator has a much thicker layer of rubber inside. The lining of the spiral stator pump is even all around the stator. Standard stator pumps require much lower tolerances than spiral stator pumps—also called even-wall progressive cavity pumps. Lower tolerances result in less efficiency and more wear in round stator designs.
Traditional, round stators also suffer extreme wear during startup. For instance, highly abrasive materials will slip or leak backward because of the cold rubber, which has not heated or expanded. This expansion of the thicker rubber in the stator is required to tighten the tolerances to allow more efficient pumping. During this time, the pump will suffer more wear or damage. With even-wall technology, these extreme tolerances are not required. The even-wall technology is more efficient at startup and during normal operation.
Figure 1. Relative flow (m3/hr) versus counter pressure (bar)
Figure 2. Efficiency (percent) versus counter pressure (bar)
Figure 2 shows the total efficiency difference measured from pump power demand. The conventional pump’s maximum efficiency is 54 percent, while the even-wall progressive cavity pump has a significantly higher maximum efficiency of 63 percent.
Higher hydraulic efficiency reduces the energy consumed, and it facilitates a longer pump service life. Backflow can cause a high degree of wear. The even-wall progressive cavity pump will have a longer service life because of the minimized backflow between the rotor and stator.
All the features discussed in this section improve pump performance but also increase pump costs. Depending on an application’s parameters and conditions, end users must select the features that are required for their process. Progressive cavity pumps offer many advantages. Some are high flow delivery in a small package, the ability to handle significant slurries and relatively low cost.
Part Two of this series discusses peristaltic pumps and how they can be a good choice for handling solids in many industries.