Liquid Flowmeters – A Guide for Selecting a （液体流量计选择一个指南）.pdf

Liquid Flowmeters – A Guide for Selecting a Flowmeter for Pressurized Systems Selecting a meter requires a first-rate technical assessment of the pressurized system and a thorough evaluation of the capabilities and needs of the operator. Technical knowledge required for metering ranges from very basic ability to read a meter and write down the rates of diversion and total use to a high level of technical ability for automated systems that enable a user to operate/control a system from almost any location (see discussion on Supervisory Control and Data Acquisition, also called SCADA). Selecting a meter for pressurized pipe systems Experts claim that over 75 percent of the flow meters installed are not performing satisfactorily, and improper selection accounts for 90 percent of problems users have with meters. Selecting a meter for pressurized systems can be confusing because 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 dealer the following basic information to make sure a meter matches the system. If not, readings and recordings will be inaccurate, and inaccuracies will not likely favor the water right holder. • 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 needed for the operator. For instance, a system may need to pump as little as 20 gallons per minute for the smallest set of water to as much as 120 gallons per minute for the largest set. The lower rate may eliminate some types of meters because the low flow may be outside the range the meter can measure. In some cases, a meter that will measure the lowest rate for a system may not be able to measure the highest rate used in that system. • A meter must be able to measure the instantaneous quantity (Qi) and record the total qua