Water Well Journal
Issue link: http://read.dmtmag.com/i/543740
negative or positive impact, particularly in rural areas. However, where the pri- mary culprit is due to overuse of open- delta power supplies, although there are various methods of control or correction possible, the best correction results often come from a derating of the pump load of up to 10%-15% (or to between 85%-90% of the motors output) based on the degree of unbalance (see Figure 2). You can expect frequent motor fail- ures and an unhappy customer if you elect to do nothing. Engine and Motor Ratings Engines and electric motors are not rated the same. In most cases you would think this is a situation where people already know this, but I still receive inquiries from individuals who don't understand the difference. To start, an electric motor is rated for output at 100% of its nameplate rating. For exam- ple, a 100 hp motor is rated to produce 100% of 100 bhp. Based on identical engine displace- ments, the relative output from a gasoline engine is typically rated at 95%-100% of its rating. A diesel engine, on the other hand, generally produces around 85%-90% of the same gas en- gine rating. A propane (LPG) engine produces about 95% and a natural gas engine produces around 80% of a gas engine output. Turbocharged engines can increase the relative output by up to 10%, but that varies with the engine. When applying any engine to an application, don't forget to add an al- lowance for what are referred to as the "parasitic loads." These are the loads over and above the required pump load and include additional load factors such as the alternator or generator, belts, fan, water pump, fuel pump, and all other auxiliary loads. Although they vary with the installa- tion and specific engine, I have found through the years that adding around 5-6 hp will generally provide the horse- power reserve needed. A final note about engines. All en- gines, particularly diesel engines, should be regularly exercised under load as car- bon buildup and temperature variations will be more severe under low loads. Load banks are often applied for this purpose, particularly for generators. Since gasoline engines operate at higher temperatures and speeds per output horsepower, the overhaul cycle for this group of engines is typically more fre- quent than diesels, up to twice, although large-bore natural gas/propane engines at slow speeds (1200-1500) can often exceed the running life of their diesel counterparts. Air-Cooled vs. Water-Cooled Engines When I started out during the late 1970s, the conventional wisdom was water-cooled engines were the best thing to use on stationary engine appli- cations and were usually how we de- signed back-up engines. Over the years, I have modified my thinking somewhat where I now believe air-cooled engines are often the engine of choice. For any engine subject to stationary, or fixed, operation, I prefer to use water- cooled diesel engines with a jacket- water cooler or an air-cooled diesel option for smaller (less than 80 bhp) applications. This is due in large part to the design advantages gained by using specific engine designs intended for sta- tionary operation. Of course, using water-jacket engine coolant systems means you must have an avenue for disposing of the reject water or adding a heat exchanger. But the differences between the downside of a fan, water pump, belts, horsepower loss, etc. against the horsepower gain, less noise, and cooler and more consis- tent operating temperatures has con- vinced me the air-cooled or water-jacket cooler system is often a better choice. But as with most decisions in life, your personal experience and individual factors are far more valuable to your choice than any other factor. Use Resisting Mass Under an Engine Although there are always exceptions to every recommendation, when given a choice I recommend using an adequate mass of resistance, typically a concrete block, to help support and resist the vi- bration from a stationary engine. I won't relate any personal experience or recom- mendation as to where and how to place this mass, but I have found the concrete works best when applied at close to 150% (1.5 times) the weight of the engine. Therefore, for an engine that weighs 1800 pounds, this would equate to a block of concrete (at 150 lbs/cubic foot) with dimensions of 2 feet width × 3 feet height × 3-4 feet length, or 1800 lbs × 1.5 = 2700 lbs ÷ 150 = 18 cubic feet ÷ 2 feet (width) × 3 feet (height) = 3 feet minimum length. ENGINEERING continues on page 40 WWJ August 2015 39 Twitter @WaterWellJournl Figure 2. Motor derating factor due to voltage imbalance. DACUM Codes To help meet your professional needs, this article covers skills and competencies found in DACUM charts for drillers and pump installers. PI refers to the pumps chart. The letter and number immediately following is the skill on the chart covered by the article. This article covers: PIA-3, PIA-6, PIC-5, PIC-7, PIE-2, PIF-1, PIF-4, PIF-6 More information on DACUM and the charts are available at www.NGWA.org.