Technical Guides

Compressed air is the most expensive utility in most plants per unit of energy delivered, and typically 20 to 30 percent of it escapes through leaks. The measurement that pays for itself fastest is not the one on the compressor outlet. It is the one that lets you prove where the air is going. Why thermal mass is the usual choice Compressed air is measured by mass or by standard volume, not by actual volume, because the same mass occupies a different volume at different pressures. A thermal mass meter reads mass flow directly, so it needs no separate pressure and temperature compensation. That simplicity is the whole argument. One instrument instead of three, and the reading is already in the units an energy audit needs. The alternatives all have a catch. A vortex meter works but needs 15 to 20 diameters of straight run that compressed air headers rarely have. An orifice plate costs permanent pressure loss, which on a compressed air system you pay for twice: once at the compressor and again at the dryer. An ultrasonic clamp-on unit works but struggles with the low density and thin pipe walls typical of air headers. Where to put the…

Steam is the hardest common fluid to measure well. It is compressible, it changes phase, it carries moisture, and the properties that determine its energy content are not the properties a flow meter measures directly. Most steam metering problems come from those four facts rather than from the instrument. Why steam is not just hot gas Three things make it awkward. Density moves with both pressure and temperature. A volumetric meter on steam measures volume, and volume tells you almost nothing until you multiply by density. That means every steam installation needs pressure and temperature inputs, either from a separate transmitter or built into the meter. Wetness. Saturated steam carrying 3 percent moisture by mass carries roughly 3 percent less energy per kilogram than the tables say. A meter measuring mass flow accurately will still give the wrong energy figure if the dryness fraction is unknown. Velocity is high. Steam runs at 15 to 40 m/s in most plants because low density forces large volumetric flow through modest pipes. That is a lot of kinetic energy, and it wears out anything with a moving part. The three technologies that actually get used Vortex The default for most industrial steam. No…

Most quotation requests we receive are missing at least two of the five numbers needed to answer them. The result is a week of email ping-pong before anyone can give a real price. Here is what actually determines the model, and why each item changes the answer. One: the fluid, and what it does to a sensor Not the product name. The physical behaviour. Does it conduct electricity? This decides whether an electromagnetic meter is even possible. Roughly 5 microsiemens per centimetre is the floor. Mains water is far above it. Deionised water, oils and most solvents are below it. How viscous is it? Below 10 cSt, turbine and vortex meters behave. Above 20 cSt, look at positive displacement or Coriolis. Is it clean? Solids and fibres foul electrodes and scatter ultrasonic signals. A full-bore magnetic meter handles them. Is it single phase? Entrained air breaks almost every technology. Steam is its own category. Two: three flow rates, not one Minimum, normal and maximum. If you only send the maximum, any meter we quote will be sized for a condition your plant rarely runs at. The minimum is the one that matters most and the one most often missing. It…

Every flow meter datasheet leads with a percentage. Almost every buyer misreads it. The difference between “plus or minus 0.5 percent of reading” and “plus or minus 0.5 percent of full scale” is the difference between a meter that holds accuracy across its range and one that quietly falls apart at low flow. Of reading, or of span Percent of reading means the error scales with the actual flow. At 10 m3/h a 0.5 percent of reading meter is within 0.05 m3/h, and at 100 m3/h it is within 0.5 m3/h. Percent of full scale means the error is fixed to the meter’s maximum. A 0.5 percent of span meter on a 100 m3/h range is within 0.5 m3/h everywhere, including at 10 m3/h, where that is a 5 percent error on the actual value. Same number on the datasheet. Ten times the real error at low flow. If you are comparing two meters and one quotes reading while the other quotes span, you are not comparing the same thing. Turndown is where accuracy lives or dies Every technology has a range over which the stated accuracy holds, and a floor below which it does not. That ratio is the…

Good flow meter troubleshooting starts with the symptom, not flow meter troubleshooting. The same symptom means different things on different technologies, and the fastest route to a fix is to know which faults are possible on flow meter troubleshooting in front of you. This guide is organised by what you see on the display. For each symptom it lists the likely causes in the order worth checking, because the cheapest check should always come first and the most expensive should come last. On this page Reading zero with flow present Reading high Reading low Erratic or noisy reading Slow drift over months Reading stuck at one value By technology: what fails first The five tools worth carrying Why records solve half the calls Common questions Reading zero with flow present Start with the pipe. Is it actually full? flow meter troubleshooting on a gravity line that runs partly empty reads zero or nonsense, and no amount of electronics work fixes it. Open a vent and see what comes out. Then check the valve. A closed isolation valve, a stuck non-return valve or a bypass left open all produce zero flow and flow meter troubleshooting that is working perfectly. This sounds…

Most flow meter selection goes wrong at the first step. Someone asks for flow meter selection guide for a DN100 line, and the conversation starts with pipe size when it should start with the fluid. Pipe size is the last thing that matters and it is the first thing people mention. This flow meter selection guide works in the order an engineer actually decides: fluid first, then range, then accuracy, then pipework, then budget. Each step eliminates options, and by the fifth step there are usually only two left. On this page Step 1: the fluid Step 2: the range Step 3: the accuracy requirement Step 4: the pipework Step 5: the budget Technology comparison Three worked examples Five selection mistakes What to send an enquiry Common questions Step 1: the fluid The fluid eliminates more options than any other factor. Gas, steam, clean liquid, dirty liquid, slurry and viscous product each have a short list, and the lists barely overlap. Gas rules out every positive displacement meter except the rotary type, and it rules out electromagnetic and Coriolis on cost. Steam rules out anything with a rotor or a sensor in the flow. Clean liquid keeps almost everything. Slurry…

Reading flow meter PID symbols is a skill that pays for itself the first time you are asked to check a drawing before a shutdown. The symbols carry more information than most people realise: what flow meter pid symbols is, where it is mounted, whether it is shared with a control system, and often what technology it uses. The trouble is that drawings from different engineering houses use different conventions, and a symbol that means one thing on an American drawing means something else on a European one. This guide covers the ISA convention that most plants follow, and points out where it varies. On this page flow meter pid symbols bubble Tag letters that matter Line types and signals Flow element symbols Symbols by meter technology Reading a complete loop Where drawings mislead A quick checking routine Common questions The instrument bubble Every instrument on a P and ID sits inside a circle or a rounded shape called a bubble. The bubble tells you where flow meter pid symbols lives, and the letters inside tell you what it does. A plain circle means field mounted, visible to the operator on the plant. A circle with a horizontal line through…

The electromagnetic vs ultrasonic question usually gets answered by conductivity, and it usually gets answered wrong because the person asking has already decided. Both meters have an empty bore, both have no moving parts, and both claim half a percent on a good day. The differences are in what they need from the installation. Here is the short version. If the liquid conducts and the pipe can be opened, an electromagnetic flowmeter is more accurate and cheaper to own. If the pipe cannot be opened, or the liquid does not conduct, an ultrasonic meter is the only option. Everything else is detail. On this page The question that decides it How each meter works Accuracy compared Installation and shutdown cost Pipe size economics Fluids each one handles Slurry and dirty liquid Cost of ownership Decision table Three real cases Common questions The question that decides it An electromagnetic flowmeter needs the liquid to conduct electricity. Below about 5 microsiemens per centimetre there is no usable signal and electromagnetic vs ultrasonic reads zero. An ultrasonic meter needs the liquid to carry sound, which almost everything does. So the first question is not accuracy or price. It is whether the liquid conducts….

The turbine flow meter working principle is simple enough to explain in a sentence: fluid spins a rotor, and the rotor spins faster when the flow is faster. Everything difficult about turbine flow meter working principle is in the second sentence, which is about how accurately that relationship holds and for how long. That second sentence is where bearings, blade geometry, K-factor curves and calibration come in. A cheap turbine meter and an expensive one use the same principle and differ entirely in how well they hold the relationship over years of service. On this page The rotor The flow straightener The magnetic pickup The K-factor Why the K-factor curve bends Bearings and service life Gas and liquid versions What changes the K-factor Calibration and traceability Installation Common questions The rotor The rotor is a light wheel with a number of flat or slightly curved blades, mounted on a shaft that runs in a bearing at each end or in a single cantilever bearing. Fluid passing through the bore strikes the blades and turns the wheel. Blade count sets the pulse resolution. A 24 blade rotor produces 24 pulses per revolution, so a low flow still generates a usable frequency….

Every vortex flow meter datasheet says fifteen diameters upstream and five downstream, and almost every installation site does not have fifteen diameters. That gap between the datasheet and the pipe rack is where most vortex meter accuracy problems begin, and it is worth understanding what the number actually buys you. The requirement is not arbitrary. A vortex flow meter infers velocity from the frequency of vortex shedding, and that frequency depends on the shape of the velocity profile arriving at the bluff body. A distorted profile changes the effective Strouhal number, and vortex flow meter straight run reads wrong in a way that looks like a calibration drift. On this page Why the requirement exists Where 15D and 5D come from What each upstream fitting costs Measuring the run you actually have Flow conditioners When you cannot get the length Downstream requirements Temperature and pressure ports Vertical and inclined lines Common questions Why the requirement exists A bluff body in a pipe sheds vortices alternately from each edge. The shedding frequency is proportional to velocity divided by body width, with a proportionality constant called the Strouhal number. For a well designed body that constant is stable over a wide Reynolds…