Flowmeter Selection

The first step in the flowmeter selection process is to identify the meters that are technically capable of performing the required measurement and have the required size, pressure and temperature ratings, and materials of construction. Once such a list has been developed, one should consider cost, delivery, performance, and other factors to arrive at the best selection. 

In the process industries, flow measurement devices are the largest market in the process instrumentation field. Two web sites for process equipment and instrumentation, www.globalspec.com, and www.thomasnet.com, both list more than 800 companies that offer flow measurement products. There are more than one hundred types of flowmeters commercially available. The aforementioned web sites not only facilitate selection and specification of commercial flowmeters, but also provide electronic access to manufacturers technical literature. 

This subsection summarizes selection and installation of flowmeters, including the measurement of pressure and velocities of fluids when the flow measurement technique requires it. 

Web sites for process equipment and instrumentation, such as www.globalspec.com and www.thomasnet.com, are valuable tools when selecting a flowmeter. These search engines can scan the flowmeters manufactured by more than 800 companies for specific products that meet the user s specifications. Table 10-4 was based in part on information from these web sites. Note that the accuracies claimed are achieved only under ideal conditions when the flowmeters are properly installed and calibrated for the apphcation. 

Selection of flowmeters In the selection of a suitable flowmeter for a particular application, care must be exercised in handling the anticipated liquid velocities. The velocity of liquid must be within the linear range of the device. For example, a flowmeter with 100 mm internal diameter can handle flows between 50 to 5,000 L/min. An optimum operation will be achieved at a flow rate of 500 L/min. 

Flowmeters. Even after modification the pumps usually showed some long-time drift in the pumping velocity, mainly due to changes in valve operation caused by corrosion, dirt accumulation or trapped air bubbles. Thus all flowrates have to be measured at regular intervals and the pumps adjusted when needed. Various devices for flowrate measurements were tested and two were finally selected. 

Batch controllers for each flowmeter are mounted in the main control panel. The emulsion preparation cycle begins when the operator enters the desired quantities of each oil type into the batch controller for the oil flowmeter. The operator selects the proper outlet valve of one of the oil storage tanks, selects the proper feed pump, and activates the batch controller. The selected outlet valve will then open automatically and the selected feed pump will start automatically. The preselected oil quantity is metered into the emulsion preparation tank. When the desired quantity has been metered, the batch controller automatically activates the closing valve downstream of the flowmeter, stops the pump, and closes the outlet valve. The operator now selects the outlet valve and feed pump for the second oil type through a switch system, reactivates the batch controller, and the described sequence is repeated. 

The types of flowmeters for this type of laboratory testing should be selected according to the experiences of the participating laboratories. This consensus selection should produce the type of meter, the size, manufacture, associated instrumentation, etc. This selection process should be extended to include the fluid conditions, the flowrates, etc. as well as the tolerances to be used in arranging these. 

The energy flowmeter was designed so that it could shift flow constrictors in the sample line. The ratio of the main flow to the sample flow was called the split of the flow separator. The capillary and valve manifold on the sample line allowed the split to be changed between four different values. This was done automatically in response to changes in the main line flow. The micro-computer of the Flow-Titrator selected the split as to keep the sample flow in the 2-4 scfh range which is the operating range of the combustion system of the Flow-Titrator. 

Select only appropriate flowmeter as per range of flow rate and fluid properties. Provide strainers before the flowmeters and clean them regularly. The screens shall be of corrosion-resistant material and may be replaced every year or earlier if necessary. 

The CL (maximum at 450 nm) is conveniently detected with a photomultiplier tube (PMT). As shown in Figure 2A, a commercially available analyzer consists of a reaction chamber, flow control valves, and flowmeters for sample air and ethene. A coaxial double tube is used as a mixing jet in the reaction chamber. Sample air and ethene flow out from the inner tube at 0.3-1.51 min and the outer tube at 20-30 ml min respectively. Ethene is supplied from a high-pressure cylinder and unreacted ethene is removed with a catalytic converter to prevent it from polluting the environment. The ethene CL method has good selectivity and fast response, and is convenient for continuous air monitoring. However, fluctuations in the sample flow rate directly affect the measurement and care must be taken in the handling of ethene. Some instruments use ethene at a lower concentration than the flammability limit (<2.75%) to prevent possible accidents. 

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