Processing Magazine

Case Study: Larox LPP Pumps are doing Well in Waste Water Treatment Facility

October 12, 2010

Todd Loudin, President, Larox Flowsys North America

A wet weather facility in Nashua New Hampshire recently purchased two Larox LPP-D25 peristaltic dosing hose pumps and four Larox LPP-M peristaltic metering tube pumps. This waste treatment facility will utilize the Larox LPP-D25 dosing pumps for control of sodium hypochlorite for disinfection. These pumps were ordered with a special Halar coating for protection against the aggressive sodium hypochlorite in the unlikely occurrence of a hose failure. The LPP-D25 pumps were also equipped with hose leak detection to shut the pump down in the event of a hose failure and were with an integral variable speed motor with 4 – 20 mA input for control. The Larox LPP-M tube pumps will be utilized in the pumping of sodium bisulfite. These pumps are a highly sophisticated and fully equipped metering tube pumps.

The difference between hose and tube pumps

You may wonder what the distinction is regarding tube and hose pumps. Typically hose pumps have large diameter, they utilize a reinforced rubber hose and they also have a glycerine bath for lubrication. In shoe designs the lubrication is utilized for heat dissipation.

Tube pumps have usually a smaller diameter and they utilize tubes that are extruded from materials like Norprene, Tygothane or other engineered materials. Tube pumps do not have a glycerine bath. A large majority of simple tube pumps is limited to 2 or 4 bar pressures. More advanced tube pumps are capable of pressures up to 8.5 bar and have very sophisticated functions and based on electronics features. Most hose pumps, on the other hand, can produce up to 10 bar pressures as standard and are capable of various levels of control capabilities.

Only one compression per revolution

Larox LPP series of tube and hose pumps is very unique compared to many competitors’ pumps. The Larox hose pumps incorporate a unique rolling compression of the hose based on an eccentric cammed shaft that utilizes a roller to compress the hose. This roller compresses the hose only once per every 360 degree revolution. All other hose pumps utilize two or more shoes to compress the hose every 360 degree revolution: thus the hose is compressed two or three times more frequently in normal operation. As the number of compressions is the single most important determining factor in how long the hose will last, this feature plays very important role.

Since a roller is incorporated in the Larox Flowsys hose pumps there is virtually no friction and heat build-up that is typically associated with the sliding shoe style hose pumps. The frictional heat drastically affects the performance of sliding shoes style devices as it limits the pumping volume and the continuous operation of that kind of hose pumps. Any heat creation may be very harmful for pumping mediums that are sensitive to heat. For example sodium hypochlorite, widely used in water treatment industry, easily crystallizes when exposed for heat creating severe operational problems. Larox Flowsys hoses typically last 3 – 5 times longer than those of other hose pumps which equates to considerable savings over the life cycle of the pump.

The LPP-M metering peristaltic tube pumps mentioned above have some impressive features such as:

  • 8.6 bar pressure capability
  • Patented tube leak detection
  • IP 66 enclosure
  • LCD display with touch pad control
  • 4 -20 mA control and feedback in the standard product
  • Multilingual LCD display in English, German, French and Spanish
  • Auto priming function

Mechanical Diaphragm Metering Pumps vs. Peristaltic Pumps

In Nashua New Hampshire’s equipment selection process, both mechanical diaphragm metering pumps and peristaltic pumps were considered for the application. The original specification called for diaphragm metering pumps for the sodium bisulfite and hose pumps for the sodium hypochlorite.

There are advantages and disadvantages to both types of technology. Electrical diaphragm metering pumps are more energy efficient than tube or hose pumps. For instance, in a diaphragm pump the outward stroke requires a significant amount of energy, however on the return stroke there is virtually no energy requirement. In tube and hose pumps the energy requirement is constant. Please also note that electric diaphragm pumps were mentioned above and not pneumatic diaphragm metering pumps. Pneumatic diaphragm pumps are by fare one of the most energy inefficient forms of pumping technology available. Diaphragm pumps in general require a very clean pumped medium. In diaphragm pumps there are check valves. These check valves may become clogged or fail in use with dirty or solid ridden liquids. Also if these check valves become clogged then the pump is likely to lose its prime and also lose its ability to meter accurately. When this occurs, the check valves will need to be removed and maintenance will need to be performed. If the liquid is always full of solids then this can be a never ending problem with these diaphragm pumps. Diaphragm pumps are easy to prime against low back pressure but in some cases they may have difficulty creating a prime against high back pressure. Some advanced electric diaphragm pumps also have adjustable stroke capabilities. If the diaphragm pump does lose its prime and you try to regain your prime while the diaphragm pump has a shortened stroke length then you may have great difficulty priming the pump. A longer stroke will be the most successful in regaining your prime.

Peristaltic pump, both tube and hose, offers stable flow and metering capabilities under varying operating conditions. The output flow of peristaltic pumps is unaffected by the variation of discharge line pressure. Peristaltic pumps can also handle severe variation in suction line condition in regard to suction lift and viscosity; yet for the outmost accuracy in volume based metering application on site calibration is recommended.

Hose and tube pumps, on the other hand, are slightly less energy efficient than electric diaphragm pumps. However, they are much more user friendly than electric diaphragm metering pumps. Peristaltic pumps have less limitations or potential problems than diaphragm pumps. Peristaltic pumps are excellent for both clean, high solids slurries and also highly viscous materials. Peristaltic pumps will never lose their prime and in fact are very good for high suction lift applications. Peristaltic pumps do not rely on check or any valves for that matter for normal operation. These pumps actually operate as their own shut off device when the pump is stopped. When the pump is stopped the hose is under compression from the roller, thus no flow can occur through the pump. When operating with high vapour pressure (low NPSH) fluids peristaltic pumps excel due to the fact that they do not suffer from vapour blocks. Vapour blocks occur when there are trapped gases in liquid or in cases when the sudden pressure loss temporary takes the pressure under the vapour pressure of the liquid. These gases may accumulate in one point in the system creating vapour blocks or loss of prime. Peristaltic pumps can also run dry for any length of time without damage to the pump. If you have particulate in your pumped medium, limitation in operator experience and limitations in maintenance resources then the hose and/or tube pumps are your best alternative.

Peristaltic pumps used as thickener or clarifier underflow pumps are recommended for any thickened slurries, sludges, grids or thickening applications. Peristaltic pumps are widely used in mineral processing applications where solids content exceeds 30% or particle size causes reliability issues. The control properties of peristaltic pumps in underflow applications with high positive pressure in suction side are excellent due to the fact, that pump’s flow rate is directly proportional to the pump speed. As mentioned earlier, no flow can pass through the pump when it is not idle; neither can siphoning phenomenon nor gravity feed effect the flow. These features together mean that the control ability of the tube or hose pump is 100 % trough out the whole operating range, flow range being 1:10 with hose pumps and 1:100 with tube pumps. Peristaltic pumps can handle solid particles up to a quarter of the diameter of the hose bore’s nominal size. On the other hand, suction capabilities - almost full vacuum at any given application - can help to clear any blockages caused by foreign particles or sedimentation.

Technical Merits, Commercial Merits and Long-Term Operational Advantages Were the Reasons to Choose Larox Flowsys

In the decision process of the Nashua New Hampshire Wet Weather facility all of these factors were discussed and considered. The original specifications included both diaphragm pumps and hose pumps. Larox Flowsys offered the new Larox LPP-M tube pumps in lieu of the diaphragm pumps and offered its new eccentric rolling design hose pumps in lieu of the specified shoe design hose pumps. Larox Flowsys was selected based on both the superior tube pump and control technology of the LPP-M tube pumps as well as the operating cost savings of eccentric design savings. The engineering consultant, the city of Nashua New Hampshire elected officials and contractor all formed a common consensus to order and approve the use of Larox Flowsys tube and hose pumps. Larox Flowsys won on the technical merits, commercial merits and long-term operational advantages. This is one of many United States cities and municipalities selecting Larox Flowsys technology in lieu of inferior pumping technologies.

Larox Flowsys is the preferred supplier of flow control solutions for the most demanding media. We focus on abrasive, corrosive and other demanding shut-off, control and pumping applications serving a wide range of process industries worldwide.

Larox Flowsys heavy duty valves and peristaltic pumps have proven their suitability for a wide range of industries and applications. We work in partnership with our clients to specify, design and deliver the optimal solution. We offer reduced total cost of ownership through improved performance, longer service lifetime and lower maintenance costs.