Water flowcalc

[chan]

I have the pipe dia and the water flow in l/s. Hoe do I measure the actual flow with only a pressure guage

[Brian_UK]

You need an orifice to enable you to measure a pressure differential.

[chan]

How does one convert l/s into kpa. We have the pipe dia in mm

[The Viking]

I have the pipe dia and the water flow in l/s. Hoe do I measure the actual flow with only a pressure guage

Well, you don't...

To be able to measure the flow by observing pressure, you need to measure pressure difference across a known resistance in the pipework.
For example; across an orifice or a plate heat exchanger.

[chan]

OK so how does one determin that the flow rate in a system is as it is designed. What is the correct instrument that should be used?

[The Viking]

How does one convert l/s into kpa. We have the pipe dia in mm

KPA is a measure of pressure.
l/s is a measure of flow......

Under certain given condition there will be a relationship between them.
Therefore you would have to put one in to a formula to calculate the other.
(That formula will depend on measuring device used)

But you will not be able to "convert" one to the other.

[Josip]

Hi, chan

OK so how does one determin that the flow rate in a system is as it is designed. What is the correct instrument that should be used?

water flow meter

Best regards, Josip

[The Viking]

OK so how does one determin that the flow rate in a system is as it is designed. What is the correct instrument that should be used?

Click on THIS link.
That document shows a balancing valve with built in measuring point.
After that has been installed, you would measure the pressure drop between the 2 ports (pointing down from the valve body in the colour picture).The Red port would read a slightly higher pressure than the Blue one.
Then you would be able to find out the flow by checking the pressure drop against a graph supplied by the valve manufacturer.
(THIS is the type of pressure meter you would require for the job.)

But there are other ways of measuring water flows, as Jossip says, use a water flow meter. These could be piped in, ultrasonic, magnetic and so on.

[DEVIL]

whell to be more streghit, to messure a flow u need a pressure diff, and a pipe diamenther, because withe one pressure gage u only have one pressure, so the system might be on a hight presure on a low pressure, depending and the building hight, and pressure loss on the fan coil, or whatever u have.
So ... by nessuring the the difference u reduce the problem to one pressure, and u get the formula for how muth whater flow do u get for that dyamenther on that pressure.
And that's the closest u get to what a flow mether calculates

[Josip]

Hi, chan

I have the pipe dia and the water flow in l/s. Hoe do I measure the actual flow with only a pressure guage

....., I read your post again .... you have your flow, why you need pressure

....can you explain a little more problem you have, maybe

Best regards, Josip

[Brian_UK]

I wonder if he means that he has the design flow rate ?

[Thana]

To mearsure the flow correctly you need to know the design pressure drop and measure the actual drop with a pressure gauge or perflow meter, in a binder point near the point you are measuring.. on and off..
So i.e. if you have the design pressure drop divide this by the actual pressure drop you read, then square root it..times this by the design flow rate this will then give you the actual flow rate in l/s..but remember the temp diff you are looking for, this will have an effect on the flow rate. So not as easy as just reading a flow rate....

[Billy Ray]

Hi Viking,

thats looks like a nice flow meter!

Are they accurate & do you know how much they cost?

Billy Ray

[The Viking]

Hi Viking,

thats looks like a nice flow meter!

Are they accurate & do you know how much they cost?

Billy Ray

Accurate, YES

Cost...An arm and a leg and then some, we normally rent them.

But if you contact BSRIA they will be able to quote you. (www.bsria.co.uk)

[wdrzal]

You need an orifice to enable you to measure a pressure differential.

A mass flow meter is used to measure pressure differantial across a orfice or a pressure differantial.It requires 2 access points and a thermocouple for temperature. Mine has a pressure accuracy of .02 psi.

Or you can use a non-invasive Doppler/ultrasound to measure the flow rate inside the pipe/tube. The hand held one I have has a sensor that straps to the pipe,it runs on 45 volt (5 - 9v batteries). The doppler shift picks up any bubbles or turbulance to give a reading in feet per second.Then by using a simple formula you can calulate the flow.

[US Iceman]

If using a flow meter you need to ensure the instrument is not connected right after an elbow or control valve also. These introduce inaccuracies that can lead to incorrect readings.

[Billy Ray]

Thanks Viking,

Billy ray