Nashua New Hampshire is one of many United States cities and municipalities selecting Larox Flowsys technology over inferior pumping technologies. A wet weather facility in Nashua New Hampshire several years ago purchased two Larox LPP-D25 peristaltic dosing hose pumps and four Larox LPP-M peristaltic metering tube pumps. This waste treatment facility utilizes the Larox Flowsys 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 LPPD25 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 and sodium hypochlorite. These pumps are a highly sophisticated and fully equipped metering tube pumps.
Only one compression per revolution
The Larox LPP series of tube and hose pumps is very unique compared to competitors’ pumps. The Larox
hose pumps incorporate a unique rolling compression of the hose based on an eccentric cam 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 Larox Flowsys LPP-M metering peristaltic tube pumps have some impressive features such as:
- 125 psi 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 far 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 pumps, both tube and hose, offer 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 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 valves (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, grit 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 10:1 with hose pumps and 2500:1 with tube pumps. Hose pumps can manage a significantly wider flow range with a VFD. 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 over inferior pumping technologies. We are happy to say after two years the pumps are still operating flawlessly without any downtime.