Know Your Pitot

Flow Control Network

<<The multi-port averaging Pitot tube, a variation of the instrument invented by Henri Pitot in 1732, offers many features that make it suitable as the primary element in the measurement of liquid, steam or gas in process industry applications. As an insertion-type flowmeter, it is easily and quickly installed through a small hole drilled into the pipe. As a mechanical device with no electronics or moving parts, it is not subjected to electrical drift or physical wear, making it a dependable, repeatable primary element that needs no periodic recalibration.>>

Why Measuring Flow is a Difficult Task

Flow Control Network

<<Measuring flow is not easy. The barriers to achieving accurate and reliable flow measurements are many and varied, and even worse, these problems and issues are often interrelated.>>

Flow Measurement

McMaster University Process Control Education

<<Flow measurement is critical to determine the amount of material purchased and sold, and in these applications, very accurate flow measurement is required. In addition, flows throughout the process should the regulated near their desired values with small variability; in these applications, good reproducibility is usually sufficient. Flowing systems require energy, typically provided by pumps and compressors, to produce a pressure difference as the driving force, and flow sensors should introduce a small flow resistance, increasing the process energy consumption as little as possible. Most flow sensors require straight sections of piping before and after the sensor; this requirement places restrictions on acceptable process designs, which can be partially compensated by straightening vanes placed in the piping. The sensors discussed in this subsection are for clean fluids flowing in a pipe; special considerations are required for concentrated slurries, flow in an open conduit, and other process situations.>>

How to Choose an Insertion Flowmeter

FlowControlNetwork.com

<<Many industrial process plants have the same problem: how to put in a new flowmeter without shutting down the plant. Fortunately, there is a class of flowmeters designed expressly for this purpose. They are called insertion flowmeters because they are designed to be inserted into an existing line.>>

The Effects of Piping Run on Measurement

FlowControlNetwork.com

<<Elbows require 20 or more diameters of straight run after them. You may have to supply many more diameters of straight run if there are two elbows out-of-plane, to control the spiral twist that this piping configuration puts on the flow profile. Control valves can require at least as many straight run diameters as an elbow between themselves and the flowmeter. Even the close-coupled shutoff valve at the outlet of the flowmeter will provide perturbation in the flow profile, as will the outlet elbow.>>

Flowmeter Selection Guide [DOC File]

MIT Design that Matters

<<Numerous types of flowmeters are available for closed-piping systems. In general, the equipment can be classified as differential pressure, positive displacement, velocity, and mass meters. Differential pressure devices (also known as head meters) include orifices, venturi tubes, flow tubes, flow nozzles, pitot tubes, elbow-tap meters, target meters, and variable-area meters.>>

Metering Selection Guide

FMC Measurement Solutions

<<Answer a few application questions and let our meter selection guide choose the most appropriate meter types and sizes to ensure optimum measurement performance. The guide will provide you with meter technologies, benefits and links to technical literature based on your service conditions. You will also be given the opportunity to contact one of our application experts for more information regarding the right equipment selections for your operation, giving you a comprehensive answer to your application challenges.>>

Meter Tubes Specifications (PDF File)

FMC Measurement Solutions

Fundamentals of Orifice Meter Measurement

Daniel Measurement and Control

<<New measurement technologies are flowing through the stream measurement marketplace. New flowmeters such as ultrasonic, vortex, and Coriolis are causing a fundamental shift in the market away from traditional technologies and towards the new technologies. User concerns with reliability, cost of ownership, maintenance requirements, and improved accuracy are driving these changes. Differential pressure (dp) flowmeters are squarely in the middle of this change. Dp flowmeters use a primary element to place a constriction in the flow stream, causing a drop in pressure. The device’s transmitter uses the resulting pressure drop to calculate the flow rate. Flow rate is proportional to the square root of the difference in pressure, and is calculated using Bernoulli’s equation.>>

API-AGA14.3 Part2 Year 2000 Revisions (2.3MB PDF File)

Emerson Process Management

Raising the Bar for Primary Elements

Control Engineering Online

<<New measurement technologies are flowing through the stream measurement marketplace. New flowmeters such as ultrasonic, vortex, and Coriolis are causing a fundamental shift in the market away from traditional technologies and towards the new technologies. User concerns with reliability, cost of ownership, maintenance requirements, and improved accuracy are driving these changes. Differential pressure (dp) flowmeters are squarely in the middle of this change. Dp flowmeters use a primary element to place a constriction in the flow stream, causing a drop in pressure. The device’s transmitter uses the resulting pressure drop to calculate the flow rate. Flow rate is proportional to the square root of the difference in pressure, and is calculated using Bernoulli’s equation.>>

One Person's Opinion: Pumps and Flow Controls

Engineered Systems

<<Selecting the right flowmeter, and even more importantly, installing it correctly, are critical for the proper operation of the building automation system (bas). Flowmeters that are not selected correctly or that are not installed correctly can produce large errors and cause a great deal of trouble. The first step in selecting the right flowmeter for the application is to compare the flowmeter specifications with the actual application. You have to look at the specific piping, pressure, and temperature conditions, and make sure that the flowmeter is going to be operating in the optimum portion of its measurement and operating range.>>

Advanced Differential Pressure Flowmeter Technology

Flowmeter Directory

<<The V-Cone's remarkable performance characteristics, however, are the result of its unique design. It features a centrally-located cone inside the tube. The cone interacts with the fluid flow, reshaping the fluid's velocity profile and creating a region of lower pressure immediately downstream of itself. The pressure difference, exhibited between the static line pressure and the low pressure created downstream of the cone, can be measured via two pressure sensing taps. One tap is placed slightly upstream of the cone, the other is located in the downstream face of the cone itself. The pressure difference can then be incorporated into a derivation of the Bernoulli equation to determine the fluid flow rate. The cone's central position in the line optimizes the velocity profile of the flow at the point of measurement, assuring highly accurate, reliable flow measurement regardless of the condition of the flow upstream of the meter.>>

Ultrasonic Flowmeter Basics

Sensors Online

<<Doppler and transit-time flowmeters are gaining ground in liquid, and in some instances gas, flow measurement applications. Understanding how they work will help guarantee optimum performance.>>

Flowmeter Selection Requires a Thorough Understanding of Process Operating Conditions and Equipment Performance Requirements

PlantServices.com

<<There are many different types of flowmeters, with an ever-increasing number of design variants for each type. Moreover, advances in manufacturing processes and materials have opened new applications for these devices. Selecting the proper meter for a particular application requires a thorough understanding of process operating conditions and equipment performance requirements. Process operating conditions include estimated minimum and maximum flow rates, operating temperature and pressure, and physical properties such as operating viscosity, density or specific gravity, abrasion, and corrosivity. Performance requirements are determined by operating constraints, notably accuracy and rangeability. Flowmeter accuracy is the relative degree of freedom from error, specified as a limit that must not be exceeded. Rangeability is the ratio of maximum to minimum operating capacity within a specified accuracy tolerance limit. Following is a guide to eight popular types of flowmeters, including application advantages and limitations.>>

Straightening Vanes

North Star Flow Products

<<The use of straightening vanes in meter runs serves a twofold purpose: The turbulence often created in a complex piping system is straightened and smoothed to a normal flow pattern; the amount of straight pipe required preceding an orifice is reduced.>>

Applying Vortex Shedding Flowmeters

Control Engineering Online

<<Vortex flowmeters are applied in many processing industries and users will increasingly select this type of flowmeter as an alternative to differential pressure based flowmeters. However, vortex flowmeters can be misapplied or may not function properly. Typical examples of this are situations where pulsation and/or vibration levels are too high, the Reynolds number and/or flow velocity is too low, or flashing/cavitation of liquid occurs. Meter factors are influenced by upstream pipe configuration, which does affect the meter accuracy. Improper sizing may result in the meter not meeting its intended turndown ratio. Therefore, prior to selection and sizing, it is of major importance to carefully evaluate each individual application to ensure that misapplications are avoided. Vortex flowmeters can be used on a wide range of fluids: pure liquids or a homogeneous mixture of liquids, gases and superheated steam. They are less suitable for high viscous liquids. Solids in the fluids should be avoided, because of possible detrimental erosion effects on the bluff body.>>

Flowmeter Selection Isn't Easy, But Tools Are Here

Control Engineering Online

<<The importance for measuring flow can vary from very high, such as custody transfer, to relatively noncritical, such as recordkeeping. Regardless of why a user wants to measure flow, the challenge is to select the most applicable technology. The number of ways to measure flow is right up there with all the other primary process variables of pressure, temperature, and level. Over the years, many ingenious and enterprising methods have been brought to the market, some falling by the wayside due to the demands of accuracy, rangeability, erosion, impurities, or temperature variations. Many technologies have survived, presenting the user with the difficult decision of which to choose.>>

Liquid Flowmeters (excellent reference)

Omega Engineering, Inc.

<<An overview of types and capabilities, plus guidelines on selection, installation, and maintenance. Measuring the flow of liquids is a critical need in many industrial plants. In some operations, the ability to conduct accurate flow measurements is so important that it can make the difference between making a profit or taking a loss. In other cases, inaccurate flow measurements or failure to take measurements can cause serious (or even disastrous) results.>>

Sonic Flow Through Orifices, Nozzles and Venturis

Optimal Systems Limited

<<The vena contracta is bounded by a zone of recirculating gas immediately downstream of the orifice. Once sonic velocity has been achieved, further reduction of the downstream pressure cannot further increase the velocity through the vena contracta, but if the orifice plate is thin, it can increase the vena contracta's size. This is because as shown in the above figure, the recirculating gas zone extends upstream of the vena contracta, and that zone's shape can be affected even though the flow is sonic. Further reductions in downstream pressure cause the vena contracta to move upstream and to consequently increase in area. Ultimately, at high pressure ratios, the vena contracta can reach the upstream edge of the orifice, when its area would equal that of the orifice and the discharge coefficient would be unity.>>

Differential Pressure Flowmeters (with sidebar links to other types)

Omega Engineering, Inc.

<<The calculation of fluid flow rate by reading the pressure loss across a pipe restriction is perhaps the most commonly used flow measurement technique in industrial applications (Figure 2-1). The pressure drops generated by a wide variety of geometrical restrictions have been well characterized over the years, and, as compared in Table 2, these primary or "head" flow elements come in a wide variety of configurations, each with specific application strengths and weaknesses. Variations on the theme of differential pressure (d/p) flow measurement.>>

Coriolis Technology - Flowmeters for the Masses

Plant Services on the Web

<<The advantages of the Coriolis mass flowmeter are only beginning to be realized. Operations and maintenance and repair organizations (MRO) people alike are sometimes reluctant to apply these instruments because of their perceived high initial cost as well as a belief that a Coriolis meter is a special instrument intended for special applications. When introduced in 1977, these meters became the first commercially viable device capable of measuring the mass flow directly, as opposed to volume flow of liquids and gases. Direct mass measurement was a major advancement for the process industry, which is--or should be--more interested in metering mass than volume to ensure the tightest control. Unlike volume, mass is unaffected by changes in pressure, temperature, viscosity, and density. Although Coriolis meters directly measure mass, they can also be employed to perform volume and density measurements.>>

The Photo-Pitometer, An Instrument for Measuring Velocity in Water Mains

Scientific Medical and Mechanical Antiques

<<By the turn of the century, city water works had taken advantage of technological advances in filtration and hydraulics. But, while huge pumping engines were providing a surplus of water, many city water systems were losing over 50% of their capacity to leaks in already aging iron mains. The many miles of iron pipe buried under streets were frequently ignored, at great expense to the water departments. But, with the invention of the portable pitometer, underground water pipes could be monitored at will. A standard 1" corporation cock fitting allowed introduction of the pitot tube and permanent street connections provided an instant setup of the pitometer. The recording pitometer made a continual record of the water velocity as downstream valves were closed to determine where leaks or illegal bypasses existed.>>

Flowmeter Selection Guide

Omega Engineering, Inc.