flow rate

In physics and engineering, in particular fluid dynamics, the volumetric flow rate (also known as volume flow rate, rate of fluid flow, or volume velocity) is the volume of fluid which passes per unit time; usually it is represented by the symbol Q (sometimes V̇). The SI unit is cubic metres per second (m3/s). Another unit used is standard cubic centimetres per minute (SCCM).
In hydrometry, it is known as discharge.
In US customary units and imperial units, volumetric flow rate is often expressed as cubic feet per second (ft3/s) or gallons per minute (either US or imperial definitions).
In oceanography, the sverdrup (symbol: Sv, not to be confused with the sievert) is a non-SI metric unit of flow, with 1 Sv equal to 1 million cubic metres per second (260,000,000 US gal/s); it is equivalent to the SI derived unit cubic hectometer per second (symbol: hm3/s or hm3⋅s−1). Named after Harald Sverdrup, it is used almost exclusively in oceanography to measure the volumetric rate of transport of ocean currents.
Volumetric flow rate should not be confused with volumetric flux, as defined by Darcy's law and represented by the symbol q, with units of m3/(m2·s), that is, m·s−1. The integration of a flux over an area gives the volumetric flow rate.

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  1. W

    Shower flow rate had dropped!

    Would really appreciate thoughts, opinions & advice from the professionals. Our shower flow rate had dropped from approx 6 litres a minute to 3 litres a minute (I test thing by simply holding a 1 litre plastic jug under the shower & counting how many times it fills in a minute!). We have a...
  2. D

    Wallstar 12/14 flow rate

    Hello everybody, i am new to this forum and hope to get lots of helpful advice from it and look forward to peoples responses already. Firstly i am not a plumber but do have some basic knowledge of plumbing. A friend of mine has just bought a house which has a Wallstar 12/14 oil boiler. It is a...
  3. H

    Max flow rate

    What would be max flow rate of a Part 2 float valve?
  4. M

    Low flow rate

    Had a call today to look at problems with an installation. vaillant system boiler with unvented, weather comp and solar. Flow rate is right down. The customer is sure it used to be better. Checked at the kitchen sink, 12l/min. Only 15mm incoming but we've got fantastic pressure round this way...
  5. N

    Low mains flow rate - what to do?

    Hi, Apologies for the lengthy post, especially as it's my first here ... We've suffered from appallingly low flow rate from our mains water supply since we moved in 18 years ago. Now we're having some major extensions built I figured it's about time I did something about it. The...
  6. plumb_know

    Overcoming poor flow rate

    Sorry for the essay :) I hold BPEC unvented card, just seeking more experienced engineers advice job Back ground: customer bought house and inherited poor flow rate to (210litre) unvented megaflo in loft. Location of internal stopcock is in middle of house in downstairs toilet. Mains is...
  7. A

    Flow rate of main incoming tap different types of valve

    Hey all, I currently have a turn type valve on the incoming water supply, not the lever type. My plumber suggested changing it to a ball lever (full bore fitting) and it will be less resisitive so could help get our flow rate up. I have done a quick bit of research and assuming i have a gate...
  8. B

    Kitchen Tap lacking previous flow rate, needing help!

    Hi all, I replaced the tap washers in a bath and filled the hot water circuit back upagain (gravity hot water cylinder). I removed the airlock that was present and allhot water outlets were working fine. However, a day or so later the kitchen hottap, ONLY, has almost halved its...
  9. T

    2.2 Bar mains and poor flow rate, combi system.

    Hi chaps recently brought a new house average 3 bed terraced. Had a back boiler with cylinder ripped it all out with all new pipework and rads and got my mate to fit a cdi 32kw compact in the loft as I'm not GSR yet as I mainly do maintenance and bathrooms. anyway I'm finding the pressure on...
  10. K

    Low flow rate and hardly any pressure :)

    Alrighty guys! monday i will be returning to a job to have a better look. the guy has an absolute hard on for having an unvented cylinder but there is sod all pressure or flow rate as it is. flow rate is so low you can't get a dynamic pressure but static is 3 bar tuesday a pipe boring company...
  11. T

    water flow rate for new boiler

    Hello, we was told by an engineer our water flow rate was 10 litres per minute. I just wanted to know whether or not it makes a difference to the cost of running the boiler or any other difference if a new boiler was installed with a higher flow rate than this e.g we were recommended the...
  12. M

    Combi with highest flow rate? I've got 25 lt/min dynamic...

    As per title, need to quote for a property with 25lt/min dynamic flow rate and 3.5 bar. He is adamant that he doesn't want an unvented. So, what combi delivers that kind of performance??? I'm surprised and little dismayed that even the biggest of the Intergas range won't go higher than 18lt/min...
  13. B

    Low flow rate low pressure

    I recently changed a set of taps in an upstairs flat it has a hot water cylinder with Immersion heater all electric no rads etc what can I do? I didn't drain the cylinder only turned mains stop tap off and turned bath taps on to drain the water ? Any ideas keep seeing 'faucet' but the new taps...
  14. C

    Mains water flow rate 2 litres lower than the rate the boiler can heat.

    If the flow rate at your cold mains tap is 12 liters per minute measured with a measuring cup and you get a combi gas boiler that can heat water at 14 liters per minute what effect will it have on the boiler? I may be able to upgrade the mains lead water pipe at some time which would increase...
  15. J

    Equalising flow rate ?

    Hi All, Apologies for a long post.... I would really appreciate thoughts from someone more knowledgable with plumbing than me ! I've just had plumbers round to try and resolve a problem with hot water. The guys that came round didn't really seem to know what they were doing, and are now...
  16. S

    low flow rate

    hi guys, ok, heres the deal.. im about to start work on .large 4 bed property, will have main bath with mixer shower and two en suite with electric shower plus full 15 rad heating system... had ss water out and only getting 18 litres a min on street so a new main wont help with the 16 litres a...
  17. D

    Flow rate with Grohe Euro fittings?

    The flow rate from my cheap n cheerful unbranded 'Chinese' monobloc mixer tap was worse than the old tap it replaced. I decided to upgrade to a Grohe unit (assuming it would be good gear as they are a premium brand) and thought about changing the mini isolating valves to proper lever type cut...
  18. S

    new boiler + unvented cylinder - mains flow rate at 14 l/m

    Dear all - first post, having spent sometime reading the various posts related to flow rates, unvented cylinders and new boilers, I think I need some advice: - 1 bathroom + 1 shower, possibly another one to be added - water flow rates on 1st floor are very poor; upstairs bath / shower is poor...
  19. gassafe

    Flow rate comparison s or y?

    Went to quote a boiler recently, 18 rad system, and was surprised to see a little 22mm mid pos valve in the airing cupboard. Customer says some rads struggle to heat, its a 28kw system at present. I am going to quote a 30 cdi sys, would it be beneficial to change to a 28 3 port in airing or...
  20. S

    Can you still buy non-eco high flow rate taps for baths / utility room sinks?

    We have a new bath mixer tap, and it now takes an eternity to fill a bath. Pressure is 2.3 bar, and flow rate is about 6 litres per minute. I've looked into this, and it seems that with a view to saving water, almost all contemporary taps restrict flow rates to 6 litres per minute or less, so...
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