The wetted parts such as the disc and spindle are usually bronze, rubber, aluminum, neoprene, Buna-N, or a fluoroelastomer such as FKM. Optical or magnetic sensors are used to encode a pulse train proportional to the rotational speed of the helical gears. Some corrosion-resistant designs are made from plastic materials such as PVC. The frequency of the resulting pulse train is a measure of flow rate, while the total number of pulses gives the size of the batch. The accuracy of these meters is required to be ±2% of actual flow rate. Insertion turbine meters can be designed for gas applications (small, lightweight rotor) or for liquid (larger rotor, water-lubricated bearings). On low density fluids (SG < 0.7), the minimum flow rate is increased due to the reduced torque, but the meter's accuracy usually is not affected. As the flow passes through the chamber, the displacer piston is moved downstream. 6 In order to protect against this, the downstream pressure must be held at a value equaling 1.25 times the vapor pressure plus twice the pressure drop. Upper limit on viscosity is 10,000 centipoise. Flowmeter/totalizers display both the flow rate and the cumulative flow volume. Figure 3-9: Click on figure to enlarge. This type of meter has a sealing disc between the measuring chamber and the register. Whether functioning through a relay contact or a ramp function, these features serve to minimize splashing or overfill and to accurately terminate the batch. Under lower pressure conditions, typical rangeability is 20:1 with ±1% linearity. Viscosity affects the accuracy and linearity of turbine meters. Because the lobe gears remain in a fixed relative position, it is only necessary to measure the rotational velocity of one of them. ambient temperatures and at up to 30 psig pressures, this meter is claimed to provide accuracy to within 0.25% of reading over a 50:1 range and 0.5% over a 100:1 range. They consist of an orifice in the main line and a rotor assembly in the bypass. Rotameters require no external power or fuel, as they use the force of the fluid and gravity to measure flowrate. Metering pumps are PD meters that also impart kinetic energy to the process fluid. 4 Equalizing the inlet and outlet pressures eliminates slip flows, leakage, and blow-by. Dividing the volume of the chamber by the time it takes for the displacer to move from one detector to the other gives the calibrated flow rate. These meters are available is sizes 2 in. Also, the maximum flow through this meter is less than for the same size oscillatory piston or nutating disc meter. Flow velocities under 1 ft/sec can be insufficient, while velocities in excess of 10 ft/sec can result in excessive wear. If the process fluid viscosity is greater than 10 centipoise and the flowrate is above 20% of rated capacity, accuracy of 0.1% AR can be obtained. 12 The minimum upstream straight pipe-run requirement is 20 pipe diameters. ), ( The tubing can be silicone-rubber or, if a more corrosion-resistant material is desired, PTFE tubing. In the United States, the AWWA sets the standards for turbine flow meters used in water distribution systems. Repeatability is generally not greatly affected by changes in viscosity, and turbine meters often are used to control the flow of viscous fluids. Variable Area Meters Provide precise visual indication of rates of flow of air, liquids and industrial gases. Flow ranges from 0.04-40 gph are typical. Turbine flowmeters are commonly used to track total fuel gas (e.g. This rate is then compared to the reading of the flow meter under test. ), Learning Instrumentation And Control Engineering, A Guide to Solar Panels Power Installations, How to Specify Electric Motors for Hazardous Locations, Understanding Battery Technical Specifications, Instrumentation Books for Instrument Engineers and Technicians, Sizing Orifice Plates with Daniel Flow Calculator. NPT 1/2" to 2" Mechanical … They can meter flow rates from 1 gpm to 65 gpm in continuous service with intermittent excursions to 100 gpm. The first causes the meter to read high, the second results in rotor damage. Rotating vane meters (Figure 3-1B) have spring-loaded vanes that entrap increments of liquid between the eccentrically mounted rotor and the casing. These meters can be made out of a variety of metals, including stainless steel, and corrosion-resistant plastics such as PVDF (Kynar). Available are local and remote inidication models. Introduction to Venturi meters and tubes, @media screen and (max-width:1024px){ 15 $36.59. Check valves keep the fluid flow from reversing. Industrial Magmeters; Irrigation Magmeters Materials of construction include polypropylene, PVDF, TFE and PFA, brass, aluminum, and stainless steel. Higher accuracy can be achieved by calibrating the meter and by lowering its range. ), ( In all cases, bearings and shafts are designed to provide minimum friction and maximum resistance to wear. The turbine is suspended by a bearing between two hanger assemblies that also serve to condition the flow. Reciprocating piston meters are probably the oldest PD meter designs. 11 The most common mechanical flow meters are inserted into a pipe and use a turbine, wheel or paddle to measure velocity and then calculate volumetric flow by knowing the cross section … Figure 3-5: Click on figure to enlarge. Liquid systems can be calibrated in the laboratory against either a calibrated secondary standard or a gravimetric flow loop. While PD meters are operated by the kinetic energy of the flowing fluid, metering pumps (described only briefly in this article) determine the flow rate while also adding kinetic energy to the fluid. They are available with multiple pistons, double-acting pistons, or rotary pistons. Fill-Rite … ), ( Oscillating piston flow meters typically are used in viscous fluid services such as oil metering on engine test stands where turndown is not critical (Figure 3-2). Generally, turbine meters perform well if the Reynolds Number is greater than 4,000 and less than or equal to 20,000. The accuracy of turbine meters is typically given in percentage of actual rate (% AR). As in a reciprocating piston engine, fluid is drawn into one piston chamber as it is discharged from the opposed piston in the meter. whereas turbine meters intended for municipal water service are bronze or cast iron. In the rotary displacement meter, a fluted central rotor operates in constant relationship with two wiper rotors in a six-phase cycle. The maximum continuous flow of a nutating disc meter is usually about 60-80% of the maximum flow in intermittent service. Mechanical flowmeters measure flow by using an arrangement of moving parts, either by passing specific, known volumes of a fluid through a series of gears or chambers (in the case of positive displacement meters) or by means of a spinning turbine or rotor in an arrangement called a turbine flowmeter. Nutating disc meters are the most common PD meters. 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