Water Well Journal
Issue link: https://read.dmtmag.com/i/655200
time-differential relationship proportional to the flow can be obtained by transmitting the signal alternately in both direc- tions. A limitation of time-of-travel meters is the liquids being measured must be relatively free of entrained gas or solids to minimize signal scattering and absorption. Vortex flowmeters (Figure 4) make use of a natural phe- nomenon occurring when a liquid flows around a bluff object. Eddies or vortices are shed alternately downstream of the object, much like a flag flapping in the breeze. The faster the wind blows, the more the flag flaps. The flapping in liquid flows is called shedding. The frequency of the shedding is directly proportional to the velocity of the liquid flowing through the meter. The more frequent the shedding, the higher the rate of flow of water. The three major components of the flowmeter are a bluff body strut-mounted across the bore of the flowmeter, a sensor to detect the vortex and generate an electrical impulse, and a signal amplification and conditioning transmitter whose out- put is proportional to the rate of flow. The meter is equally suitable for rate of flow or for totalizing flow measurements. However, using this type of meter for slurries or high viscos- ity liquids is not recommended. Flowmeter Selection Selecting a meter requires a technical assessment of the system and a thorough evaluation of the capabilities and needs of the operator. Technical knowledge ranges from a basic abil- ity to read a meter and write down the rates, to a high level of technical ability for automated systems to operate or control a system from almost any location. Experts claim more than 75% of the flowmeters installed are not performing satisfactorily, and improper selection and installation accounts for 90% of the problems users have with flowmeters. Selecting a meter for water systems can be confusing be- cause of the different types and styles available on the market. A meter must be matched to the system, and the water user has to tell the meter vendor basic information to make sure a meter matches the system. If not, readings and recordings will be inaccurate. Flowmeter User's Guide Know the range of flow under which the system operates. Range of flow is the lowest rate of pumping to the highest rate of pumping of a system. For instance, a system may need to produce as little as 100 gpm from the smallest pump to as much as 1000 gpm from the largest pump. The lower rate may eliminate some meters because the low flow may be outside the range the meter can reliably measure. Conversely, in some cases, a meter that will measure the lowest rate for a system may not be able to effectively measure the highest rate used in that system. A flowmeter should be able to measure the instantaneous rate and also record the total volume of water used over time. The instantaneous rate is the rate at which water is pumped, such as units of 100 gpm, 1000 gpm, etc. The total volume or quantity pumped over time may be recorded as gallons, cubic feet, tens of gallons or cubic feet, hundreds of gallons or cubic feet, etc. For most uses in potable water, totalizing the total volume in cubic feet is generally best. The size of the pipe is important. Some pumping systems have pipe installed on a manifold where the diameter of the pipe is much larger than necessary for one or two of the pumps. This is often a case where the flowmeter must operate in or below the allowable low flow region of the meter. In those cases, it is not likely a meter with a reasonable cost for the system will be available. It is often best to place a smaller diameter pipe in the system and install a meter in the smaller diameter section that will measure the low flows only. Be sure all the installation requirements are met. The most critical for proper performance is making sure there is enough straight or unobstructed pipe before and after the meter, checking for the proper installation requirements, providing the proper upstream and downstream conditions, and a stable flow path before and after the metering device. Upstream ells and valves are usually the most dangerous. Read the instructions for installing the specific meter to be used. Not all meters have the same requirements. The re- quired lengths are usually a function of the diameter of the pipe. For example, if a meter requires five times the diameter of straight pipe before the meter and two times the diameter after the meter, which is a common parameter, a 6-inch pipe would need a minimum of 30 inches of straight and unob- structed pipe before the meter and a minimum of 12 inches of straight pipe after the meter. If the required length of straight pipe is not available, particularly before the meter, then straightening vanes should be required or the system re- designed away from the outlet of the pump to install a meter properly. Make sure the orientation of the flowmeter is correct. Al- though most meters can operate well in any orientation (verti- cal, horizontal, upside down), some flowmeters are designed and intended for a specific mounting. Verify your orientation DACUM Codes To help meet your professional needs, this column 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: PIC-9, PIF-6 More information on DACUM and the charts are available at www.NGWA.org. ENGINEERING from page 39 40 April 2016 WWJ Learn How to Engineer Success for Your Business Engineering Your Business: A series of articles serving as a guide to the groundwater business is a compilation of works from long- time Water Well Journal columnist Ed Butts, PE, CPI. The hardback book features 37 complete "Engineering Your Business" columns and the figures and tables that originally ran with the articles. The columns cover the groundwater industry and are divided into six areas: contractor classroom, getting started, troubleshooting pumps, rehabilitation, business basics, and tricks of the trade. Visit NGWA's Online Bookstore at www.NGWA.org for more information. waterwelljournal.com