Editing Flow measurement (section)

==Mechanical flowmeters==
A [[positive displacement meter]] may be compared to a bucket and a stopwatch. The stopwatch is started when the flow starts and stopped when the bucket reaches its limit. The volume divided by the time gives the flow rate. For continuous measurements, we need a system of continually filling and emptying buckets to divide the flow without letting it out of the pipe.  These continuously forming and collapsing volumetric displacements may take the form of pistons reciprocating in cylinders, gear teeth mating against the internal wall of a meter or through a progressive cavity created by rotating oval gears or a helical screw.

===Piston meter/rotary piston===
Because they are used for domestic water measurement, [[piston]] meters, also known as rotary piston or semi-positive displacement meters, are the most common flow measurement devices in the UK and are used for almost all meter sizes up to and including 40&nbsp;mm ({{frac|1|1|2}}&nbsp;in). The piston meter operates on the principle of a piston rotating within a chamber of known volume. For each rotation, an amount of water passes through the piston chamber.  Through a [[gear]] mechanism and, sometimes, a [[magnetic]] drive, a needle dial and [[odometer]] type display are advanced.

=== Oval gear meter ===
[[File:Caudalimetro Desplazamiento PositivoV1.jpg|thumb|right| A positive displacement flowmeter of the oval gear type. Fluid forces the meshed gears to rotate; each rotation corresponds to a fixed volume of fluid. Counting the revolutions totalizes volume, and the rate is proportional to flow.]]
An oval gear meter is a positive displacement meter that uses two or more oblong gears configured to rotate at right angles to one another, forming a T shape. Such a meter has two sides, which can be called A and B. No fluid passes through the center of the meter, where the teeth of the two gears always mesh. On one side of the meter (A), the teeth of the gears close off the fluid flow because the elongated gear on side A is protruding into the measurement chamber, while on the other side of the meter (B), a cavity holds a fixed volume of fluid in a measurement chamber. As the fluid pushes the gears, it rotates them, allowing the fluid in the measurement chamber on side B to be released into the outlet port. Meanwhile, fluid entering the inlet port will be driven into the measurement chamber of side A, which is now open. The teeth on side B will now close off the fluid from entering side B. This cycle continues as the gears rotate and fluid is metered through alternating measurement chambers. Permanent magnets in the rotating gears can transmit a signal to an electric reed switch or current transducer for flow measurement. Though claims for high performance are made, they are generally not as precise as the sliding vane design.<ref>{{cite book|last=Furness|first=Richard A.|title=Fluid flow measurement.|year=1989|publisher=Longman in association with the Institute of Measurement and Control|location=Harlow|isbn=0582031656|page=21}}</ref>

===Gear meter===
Gear meters differ from oval gear meters in that the measurement chambers are made up of the gaps between the teeth of the gears. These openings divide up the fluid stream and as the gears rotate away from the inlet port, the meter's inner wall closes off the chamber to hold the fixed amount of fluid. The outlet port is located in the area where the gears are coming back together.      The fluid is forced out of the meter as the gear teeth mesh and reduce the available pockets to nearly zero volume.

====Helical gear====
Helical gear flowmeters get their name from the shape of their gears or rotors. These rotors resemble the shape of a helix, which is a spiral-shaped structure. As the fluid flows through the meter, it enters the compartments in the rotors, causing the rotors to rotate. The length of the rotor is sufficient that the inlet and outlet are always separated from each other thus blocking a free flow of liquid. The mating helical rotors create a progressive cavity which opens to admit fluid, seals itself off and then opens up to the downstream side to release the fluid. This happens in a continuous fashion and the flowrate is calculated from the speed of rotation.

====Nutating disk meter====
This is the most commonly used measurement system for measuring water supply in houses. The fluid, most commonly water, enters in one side of the meter and strikes the [[Nutation|nutating]] disk, which is eccentrically mounted. The disk must then "wobble" or nutate about the vertical axis, since the bottom and the top of the disk remain in contact with the mounting chamber. A partition separates the inlet and outlet chambers. As the disk nutates, it gives direct indication of the volume of the liquid that has passed through the meter as volumetric flow is indicated by a gearing and register arrangement, which is connected to the disk. It is reliable for flow measurements within 1 percent.<ref>{{Cite book |last=Holman |first=J. Alan |author-link=J. Alan Holman |title=Experimental methods for engineers |year=2001 |publisher=McGraw-Hill |location=Boston |isbn=978-0-07-366055-4 }}</ref>

===Turbine flowmeter===
The turbine flowmeter (better described as an axial turbine) translates the mechanical action of the turbine rotating in the liquid flow around an axis into a user-readable rate of flow (gpm, lpm, etc.). The turbine tends to have all the flow traveling around it.

The turbine wheel is set in the path of a fluid stream. The flowing fluid impinges on the turbine blades, imparting a force to the blade surface and setting the rotor in motion. When a steady rotation speed has been reached, the speed is proportional to fluid velocity.

Turbine flowmeters are used for the measurement of natural gas and liquid flow.<ref>{{cite report|publisher =[[American Gas Association]]|title = Report Number 7: Measurement of Natural Gas by Turbine Meters|date = February 2006|url = https://global.ihs.com/doc_detail.cfm?document_name=AGA%20REPORT%20%237&item_s_key=00139712 |url-access = subscription}}</ref> Turbine meters are less accurate than displacement and jet meters at low flow rates, but the measuring element does not occupy or severely restrict the entire path of flow. The flow direction is generally straight through the meter, allowing for higher flow rates and less pressure loss than displacement-type meters. They are the meter of choice for large commercial users, fire protection, and as master meters for the [[water distribution system]]. Strainers are generally required to be installed in front of the meter to protect the measuring element from gravel or other debris that could enter the water distribution system. Turbine meters are generally available for 4 to 30&nbsp;cm ({{frac|1|1|2}}–12&nbsp;in) or higher pipe sizes. Turbine meter bodies are commonly made of stainless steel, bronze, cast Iron, or ductile iron. Internal turbine elements can be plastic or non-corrosive metal alloys. They are accurate in normal working conditions but are greatly affected by the flow profile and fluid conditions.

Turbine flowmeters are commonly best suited for low viscosity, as large particulate can damage the rotor. When choosing a meter for an application that requires particulate flowing through the pipe, it is best to use a meter without moving parts such as a [[Magnetic flow meter|Magnetic flowmeters]].

Fire meters are a specialized type of turbine meter with approvals for the high flow rates required in fire protection systems. They are often approved by Underwriters Laboratories (UL) or Factory Mutual (FM) or similar authorities for use in fire protection. Portable turbine meters may be temporarily installed to measure water used from a [[fire hydrant]]. The meters are normally made of aluminum to be lightweight, and are usually 7.5&nbsp;cm (3&nbsp;in) capacity. Water utilities often require them for measurement of water used in construction, pool filling, or where a permanent meter is not yet installed.

===Woltman meter===
The Woltman meter (invented by Reinhard Woltman in the 19th century) comprises a rotor with helical blades inserted axially in the flow, much like a ducted fan; it can be considered a type of turbine flowmeter.<ref>{{cite book|last1= Arregui|first1 = Francisco|last2= Cabrera |first2= Enrique Jr.|last3= Cobacho|first3 = Ricardo|publisher = IWA Publishing|location = London|url =  https://books.google.com/books?id=2onbCwAAQBAJ&pg=PA33 |title =Integrated Water Meter Management |page = 33|date = 2006|isbn = 9781843390343}}</ref> They are commonly referred to as helix meters, and are popular at larger sizes.

===Single jet meter===
A single jet meter consists of a simple [[impeller]] with radial vanes, impinged upon by a single jet. They are increasing in popularity in the UK at larger sizes and are commonplace in the [[European Union|EU]].

===Paddle wheel meter===
{{Unreferenced section|date=December 2024}}
[[File:TK Series Paddle Wheel Assembly.jpg|alt=Truflo TK Series Paddle Wheel Flow Meter|thumb|The paddle wheel assembly generates a flow reading from the fluid flowing through the pipe instigating the spinning of the paddlewheel. Magnets in the paddle spin past the sensor. The electrical pulses produced are proportional to the rate of flow.]]
Paddle wheel flowmeters (also known as [[Pelton wheel]] sensors) consist of three primary components: the paddle wheel sensor, the pipe fitting and the display/controller. The paddle wheel sensor consists of a freely rotating wheel/impeller with embedded magnets which are perpendicular to the flow and will rotate when inserted in the flowing medium. As the magnets in the blades spin past the sensor, the paddle wheel meter generates a frequency and voltage signal which is proportional to the flow rate. The faster the flow the higher the frequency and the voltage output.

The paddle wheel meter is designed to be inserted into a pipe fitting, either 'in-line' or insertion style. Similarly to turbine meters, the paddle wheel meter requires a minimum run of straight pipe before and after the sensor.

Flow displays and controllers are used to receive the signal from the paddle wheel meter and convert it into actual flow rate or total flow values.

===Multiple jet meter===
A multiple jet or multijet meter is a velocity type meter which has an impeller which rotates horizontally on a vertical shaft. The impeller element is in a housing in which multiple inlet ports direct the fluid flow at the impeller causing it to rotate in a specific direction in proportion to the flow velocity. This meter works mechanically much like a single jet meter except that the ports direct the flow at the impeller equally from several points around the circumference of the element, not just one point; this minimizes uneven wear on the impeller and its shaft. Thus, these types of meters are recommended to be installed horizontally with its roller index pointing skywards.

===Pelton wheel===
The [[Pelton wheel]] turbine (better described as a [[radial turbine]]) translates the mechanical action of the Pelton wheel rotating in the liquid flow around an axis into a user-readable rate of flow (gpm, lpm, etc.). The Pelton wheel tends to have all the flow traveling around it with the inlet flow focused on the blades by a jet. The original Pelton wheels were used for the [[Electricity generation|generation of power]] and consisted of a radial flow turbine with "reaction cups" which not only move with the force of the water on the face but return the flow in opposite direction using this change of fluid direction to further increase the [[Energy conversion efficiency|efficiency]] of the [[turbine]].

===Current meter===
{{Main|Current meter}}
[[File:Dumas Neyrpic Current Meter.JPG|thumb|right|alt=Spiral propeller connected to a streamlined housing, held by a hand. Wire leads at the right.|A propeller-type current meter as used for hydroelectric turbine testing]]

Flow through a large [[penstock]] such as used at a [[hydroelectric power]] plant can be measured by averaging the flow velocity over the entire area. Propeller-type current meters (similar to the purely mechanical [[Ekman current meter]], but now with electronic data acquisition) can be traversed over the area of the penstock and velocities averaged to calculate total flow. This may be on the order of hundreds of cubic meters per second. The flow must be kept steady during the traverse of the current meters. Methods for testing hydroelectric turbines are given in [[International Electrotechnical Commission|IEC]] standard 41. Such flow measurements are often commercially important when testing the efficiency of large turbines.