Given the choice, industrial pumps would not want to be used in the environmental and geotechnical drilling industry. Few applications exist where a pump is worked harder, beat up more and forced to process harsher, more abrasive materials.
In many drilling applications, slurry walls are constructed to contain contaminated ground water, divert contaminated ground water from the drinking water intake, direct uncontaminated ground water flow and provide a barrier for the ground water treatment system. The slurry, usually a mixture of a clay-like substance called bentonite and water, is pumped into the trench, which prevents the native soil from caving into the excavation. Even heavily diluted, the bentonite-water concoction is extremely viscous and can clog and significantly shorten the pump's useful life.
Mike Crimaldi understands the difficulties associated with pumping bentonite. His company, Rig Source, Inc., assists drilling contractors with a wide range of support services. With 25 years experience working in the drilling industry, the founder and president of the Elburn, Ill. based Rig Source knows the abuse that the pumps installed on many of his drilling equipment must withstand.
"The pumps on our equipment are used to process a wide variety of materials, some more abrasive and corrosive than others," said Crimaldi, who started out as the "clean-up kid" at a family-run drilling business in the Chicago area. "When we provide a rig to a customer, we have to ensure that the pump is capable of handling the specific fluid or material that the customer will be working with. If not, the entire job can go south in a hurry."
For this reason, Crimaldi relies heavily on high-pressure hose pumps. The pumps are used as primary and secondary fluid pumps for drilling and grouting. They are often assembled on the company's drill rigs, which are used mainly for auger drilling and, occasionally, soil sampling.
Positive displacement pumps like the high pressure hose pumps are typically used for moving viscous and corrosive fluids or, due to their slow-moving, smooth action, sensitive materials that require gentle handling. Diaphragm pumps and progressive cavity pumps comprise approximately 85 percent of PD pumps.
While they differ slightly in operation, most PD pumps share moving parts that come in contact with the processed material. In diaphragm pumps, ball and check valves shift up and down, while progressive cavity devices feature rotors and stators. Despite their mechanical differences, both pump types are subject to wear and tear every time abrasive materials rub against moving parts, especially metal parts that are already rubbing together.
A high pressure hose pump is a PD pump designed specifically for these abrasive materials. A hose pump, or peristaltic pump, addresses the two primary concerns associated with other pump types-wear and tear and clogging-with a mechanism considerably different from other positive displacement pumps. The peristaltic design uses a rotor that remains outside the pumpage zone, so the pump's rotor never actually touches the product being moved. Erosion of the rotor is virtually non-existent.
"You would not believe the damage we have seen some materials cause in the rotor," said Crimaldi. "There is not a rotor on earth that can handle all the abuse that our equipment faces. That is why the concept of keeping the material away from the rotor is so critical-it is the only way to virtually guarantee rotor life."
Peristaltic pumps also do not require expensive ancillary equipment-no check valves, sealing water flush systems or run dry protection. They are ideal for high-viscosity or shear-sensitive product, and are capable of processing abrasive slurries, corrosive acids and gaseous liquids as easily as water. They can run dry indefinitely without damage and have only one wetted component-the hose element. No seals, ball-checks, diaphragms, glands, immersed rotors, stators or pistons will leak, clog and corrode.
In hose pumps, fluid is drawn into a pump, trapped between two shoes or rollers (depending on the brand), and finally expelled from the pump. The complete closure of the hose, which is squeezed between a shoe and the track, gives the pump its positive displacement action, preventing backflow and eliminating the need for check-valves when the pump is not running.
Once it became evident that the peristaltic pump was ideally suited to Rig Source's applications, the only decision left was which model to select. "We had been using other pumps, but we needed a pump that took up less space, was easier to maintain and provided the same performance for a lower cost," he said.
The compact size of the chosen pump means that less deck space is used. The pumps are less expensive, and maintenance is much easier. In fact, completely rebuilding the pump is a simple operation; all that is required is to drain the lubricant, unbolt the flanges and replace the old hose. In addition, the pumps are easy to drain and winterize.
A critical pump design element directly tied to its success is the pump's direct-coupled design. The pump combines the small footprint of close-coupled pumps with the reliability and ease of maintenance of long-coupled designs. Although close-coupled pumps are extremely compact, the technology relies on the gearbox to seal the pump housing and support the heavy overhung load of the pump rotor. Close-coupled pump companies offer optional long-coupled pumps to improve gearbox and bearing life, which comes at the cost of substantially increased footprint and the added complexity of coupling alignment and maintenance.
"Close-coupled pumps and long-coupled pumps each have distinct disadvantages," said Crimaldi. "The direct-coupled design provides the benefits of each without any of the downsides."
A direct-coupled design contains heavy duty rotor bearings within the pump rotor, eliminating any overhung load. Ultra-compact high-torque planetary gearing aligns directly to the pump housing and is fully protected by an innovative buffer zone.
The machined hose element is the single most vital component for the performance, durability and efficiency of the hose pump. To ensure perfect compression and consistent, reliable performance, hose elements are manufactured from high quality compounded rubbers, reinforced with four individual layers of braided nylon and finished by high precision machining. Perfect compression eliminates slip which, in other pumps, can destroy shear sensitive product, reduce metering accuracy or allow abrasive slurries to wreak havoc on wetted parts.
According to Crimaldi, the company does offer other pumps on some of their drilling rigs. However, his preference for hose pumps is obvious.