Water Flow Rate
KY Chong
ground level (from city water supply), is it possible to know the water flow
rate ?
Parameters as follow :
1) Water pressure : 60 psi
2) Pipe size : 1.5"
Appreciate if anybody could tell me the answer
Daryn and Tracy Glasgow
L=vd^2/21.2
we can derive the following formula for pressure and diameter: (approx.)
L=2/3d^2.P^1/2
i.e. Flow in L/min equals two thirds times the diameter in mm squared times
the square root of the pressure in bar at the outlet.
In your case the outlet pressure would be taken as 60psi.
But to calculate,
60psi= 60/14.503 = 4.14 bar
1.5"= 37.5mm
Flow from your pipe is = 1907.5 L/min
This formula is derived from firefighting for calculating discharge from
hoses running at certain pressures on the fireground, it is more accurate if
you know the velocity of the water, and can then calculate the flow from
that using the first formulae.
Daryn Glasgow
KY Chong <kyc...@asia.cirquedusoleil.com> wrote in message
news:86maff$5ga$1...@clematis.singnet.com.sg...
Chris E
i dont think it came from a firefighter, though, like the other poster.....
chris
Hyatt, Ted D
The "firefighting" calculation is based on some assumptions about pipe
length and fittings.
Pressure is lost by the amount and configuration of pipe it has to
travel through. You will get a lot more flow through a straight, 1'
section of the 1.5" pipe than you will through 1000' with lots of turns.
The Bernoulli equation has been taken, along with typical pipe friction
factors and graphed to make it easier for us lazy engineers to calculate
pressure losses. Crane Flow of Fluids and ITT are two good sources on
hydraulic flow engineering. There may be some good stuff on the web
also. Do some searches for "hydraulics, flow, engineering"...
-----Original Message-----
From: Daryn and Tracy Glasgow [mailto:daz-...@ihug.co.nz]
Posted At: Wednesday, January 26, 2000 3:30 PM
Posted To: engineering
Conversation: Water Flow Rate
Subject: Re: Water Flow Rate
From the formula for flow through pipes based on velocity
L=vd^2/21.2
we can derive the following formula for pressure and diameter: (approx.)
L=2/3d^2.P^1/2
i.e. Flow in L/min equals two thirds times the diameter in mm squared
times
the square root of the pressure in bar at the outlet.
In your case the outlet pressure would be taken as 60psi.
But to calculate,
60psi= 60/14.503 = 4.14 bar
1.5"= 37.5mm
Flow from your pipe is = 1907.5 L/min
This formula is derived from firefighting for calculating discharge from
hoses running at certain pressures on the fireground, it is more
accurate if
you know the velocity of the water, and can then calculate the flow from
that using the first formulae.
Daryn Glasgow
David Blythin
According to your calculation, you are pushing 1907 l/min (496
usgal/min) through a 1 1/2" pipe. Piping designers usually try to maintain
around 7 ft/sec as a velocity that gives a good compromise between piping
costs (size of line) and line losses due to friction. A flow of 50 usgal/min
through a 1 1/2" Sch 40 pipe will have a velocity of 7.88 ft/sec,
and a line loss of 9.31 psi/100 ft. You are trying to push 10 times this
much water! For the flow you calculated, normal sizing practice would give a
6" line. Your calculation results in a velocity in a 1 1/2" line of almost
80 ft/sec - this is sheer nonsense.
There is not a simple answer to the original question - the tables would
lead you to expect a flow in the order of 50 usgpm, but the possible
variation on this is at least +/- 10 gallons/min. A cheap and nasty way of
determining the flow if you have the facility to do it is to open end your
line outside(without a nozzle) , pointing up, and measure the height the
stream reaches. Using the basic laws of motion, you can figure out the
velocity leaving the pipe, and therefore the flow.
"It could be used, however, given the small amount of available data, a
formula which calculates flow through hoses as posted previously should
suffice."
- sorry, I don't think it does suffice!
Dave
Daryn and Tracy Glasgow
and open water supplies. It is based on the difference in head between the
top of the supply and the bottom (outlet).
It too requires the velocity of the flowing water, as well as the head at
the top and bottom, as well as fluid data such as density and specific
weight.
It could be used, however, given the small amount of available data, a
formula which calculates flow through hoses as posted previously should
suffice.
Daryn Glasgow
NZFS
Chris E <ja...@ev1.net> wrote in message
news:dpNj4.2130$ht4.1...@tw12.nn.bcandid.com...
> look up "burnouli" (spelling? books are at work..) and go to town.....
>
> i dont think it came from a firefighter, though, like the other
poster.....
>
> chris
>
Chris E
sorry, but you are wrong.
mannings equation is the most commonly used equation for open channel flow.
bernoulli's is for closed conduits.
chris
ps. - pertaining to the original poster, why doesnt he just fill a known
volume and divide by the time it takes to fill it, to get discharge. divide
discharge by cross-sectional area, and he has velocity.
Daryn and Tracy Glasgow <daz-...@ihug.co.nz> wrote in message
news:86q7i5$hg6$1...@news.ihug.co.nz...
Daryn and Tracy Glasgow
Thanks for the reality check.
My application of simplistic firefighting formulae, which make perfect sense
to me, being used to pumping 7-10 bar through 70mm hose out a 32mm nozzle
which does produce flows of approx. 40-55 l/sec seemed to correlate to my
answer of 32 l/sec.
The practicalities from an engineering standpoint are now plainly obvious. I
apologise for jumping in the deep end somewhat 'half cocked'.
Daryn
David Blythin <dbly...@iaw.on.ca> wrote in message
news:s94rqpj...@corp.supernews.com...
> I'm sorry, but your figures simply don't make any sense.
> According to your calculation, you are pushing 1907 l/min (496
> usgal/min) through a 1 1/2" pipe. Piping designers usually try to maintain
> around 7 ft/sec as a velocity that gives a good compromise between piping
> costs (size of line) and line losses due to friction. A flow of 50
usgal/min
> through a 1 1/2" Sch 40 pipe will have a velocity of 7.88 ft/sec,
> and a line loss of 9.31 psi/100 ft. You are trying to push 10 times this
> much water! For the flow you calculated, normal sizing practice would give
a
> 6" line. Your calculation results in a velocity in a 1 1/2" line of almost
> 80 ft/sec - this is sheer nonsense.
> There is not a simple answer to the original question - the tables
would
> lead you to expect a flow in the order of 50 usgpm, but the possible
> variation on this is at least +/- 10 gallons/min. A cheap and nasty way of
> determining the flow if you have the facility to do it is to open end your
> line outside(without a nozzle) , pointing up, and measure the height the
> stream reaches. Using the basic laws of motion, you can figure out the
> velocity leaving the pipe, and therefore the flow.
>
> "It could be used, however, given the small amount of available data, a
> formula which calculates flow through hoses as posted previously should
> suffice."
>
David Blythin
no apologies necessary, but a reality check is always useful.
Dave
KY Chong
L=2/3d^2.P^1/2 - formula (1)
The unit for formula (1) is not tally :
L (l/min) = 2/3d^2 (mm).P^1/2(bar or kg/cm^2 )
By looking the unit of the formula, the output do not have the unit of time
(in hr/min/sec),mathematically it cannot be form up.
If this formula is established, by substituted the d=37.5mm & P=4.14bar, the
flow rate become 1907.5 L/min which is very large amount of flow from a 1.5"
pipe.
And, if i use the formula (2), L=vd^2/21.2, by substituted v=3m/s
(assumption for water velocity at 3m/s for general purpose) & d=0.0375, L =
0.1989l/s (i.e. 11.9l/min) which is relatively small compare to the first
formula.
Daryn and Tracy Glasgow <daz-...@ihug.co.nz> wrote in message
news:86o092$oa5$1...@news.ihug.co.nz...
> From the formula for flow through pipes based on velocity
>
> L=vd^2/21.2
>
> we can derive the following formula for pressure and diameter: (approx.)
>
> L=2/3d^2.P^1/2
>
> i.e. Flow in L/min equals two thirds times the diameter in mm squared
times
> the square root of the pressure in bar at the outlet.
>
> In your case the outlet pressure would be taken as 60psi.
>
> But to calculate,
>
> 60psi= 60/14.503 = 4.14 bar
>
> 1.5"= 37.5mm
>
> Flow from your pipe is = 1907.5 L/min
>
> This formula is derived from firefighting for calculating discharge from
> hoses running at certain pressures on the fireground, it is more accurate
if
> you know the velocity of the water, and can then calculate the flow from
> that using the first formulae.
>
> Daryn Glasgow
>
>