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Submersible Centrifugal pumps, Turbine pumps, Propeller pumps, Centrifugal pumps, Piston pumps, Diaphragm pumps... There are as many styles of pumps as there are applications that require them. Here are some suggested factors to be determined: Flow Required Most pumps are rated in Gallons Per Minute (GPM) with smaller pumps rated in Gallon Per Hour (GPH). If you don't know your required flow, you can determine flow base If you have a pit or pond that you want to empty in a given time, figure: Length in Feet x Width in Feet x Depth in Feet = Total Cubic Feet x 7.48 Gal/Cubic Ft. = Total Gallons. Divide the Total Gallons by the minutes you want to pump to give GPM. If you have water being supplied that is measured in Cubic Feet per Second (CFS), figure: Cubic Feet per Second x 448.8 Gal = total GPM. Total Dynamic Head Once you have the GPM established, you need to determine the Total Dynamic Head or TDH the pump must be able to produce. TDH is the resistance the pump encounters as fluid travels to discharge. TDH is the combination of vertical life and friction loss of the discharge line. Head is represented in feet. One pound of pressure equals 2.31 feet of head. Most pump dealers have line loss charts that have the information for the different types of pipeline such as PVC, steel, gated irrigation pipe, etc. Elbows, tees and valves all contribute to friction loss and need to be noted. In new installations the line size selected can have long term effects on cost. While a larger line size may be more initial investment, the long-term energy cost required may offset the investment. To assist in determining TDH, you need to supply your pump supplier with: (1) Vertical lift, (2) Length of line run, (3) Diameter of line, (4) Pipeline material, and (5) Number of elbows, tees, valves, etc. Material To Be Pumped For every pump there is a reason and vice versa. You moved your manure slurry pump into the irrigation ditch and it worked great, but when you put your spare irrigation turbine pump in the feedlot lagoon, it only lasted a little while. The flow decreased and pretty soon it wasn't working at all. The reason is internal tolerance. Pressure pumps usually have tolerances measured in thousandths of an inch and operate at direct motor speeds of 1800 or 3600 RPM. Volume pumps have tolerances measured in fractions of an inch and usually operate at speeds less than 1800 RPM and quite often at less than 1000 RPM. By combining close internal tolerances with high operating speeds, pressure pumps are generally more efficient than volume pumps when comparing GPM in horsepower required. A pressure pump subjected to abrasive fluids will have wear resulting in excessive repair costs. A volume pump run at speeds to develop pressure would require more horsepower resulting in excessive energy cost. Sometimes a single pump can't do the job and a pump system may be needed. In the example of feedlot lagoon water needing to be run through a pivot sprinkler system, a floating volume pump could supply flow to a screener or filter system. A pressure pump could then take this flow up to required pressure for the pivot sprinkler. If the filter system were in line, any pressure the volume pump could generate would decrease the horsepower requirement of the pressure pump. The total horsepower requirement should remain the same in this type of a system with the advantage being that each pump is handling a fluid within their design. A lot of pumps can provide trouble free operation if they are pumping clear drinking water a few hours a day. But when selecting a pump in a critical application and it is subjected to fluids with solids and abrasives, consider the worst case scenario. Can the fluid become dirtier at any certain time? Can the solids and abrasives be screened before getting to the pump? Does the pump need to run during those times or can it be shut down until fluid conditions improve? What can be damaged in the pump if operated during these conditions? What's the cost and time required for these repairs? Is a backup pump necessary? Does this application need more than one type of pump? Will my pump dealer or the factory have what's needed to get back into operation? When it's 102 degrees and the corn needs water --or--you just got five inches of rain and you're flooded, it would be good to have considered some of these questions. Power Sources Even with electrical costs on the rise, electric motors are still a cost effective and efficient choice if power is available Electrical line size is another consideration. A qualified electrician can advise the maximum horsepower allowed for a given wire size and length. Electrical codes vary by country and state and a qualified electrician will know the code requirements. We started out by saying you probably didn't have the time it takes to research dozens of pump styles. And now you may be thinking that coming up with just the information we have discussed appears to be a considerable task, but as you think about your application, you probably already know most of what's needed. Any pump dealer or manufacturer can select a pump based on GPM and TDH but the other details of your application, that only you know, can have a significant effect on how the pump performs in the long term. The details of your application will make sure you're comparing "apples to apples" when you compare different styles and brands of pumps. If you approach your pump supplier with all the information about your application and consider all the options, you can make an informed, cost effective, buying decision. Don't let the appeal of a lower initial cost become a long-term expense. © |
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