## Flow from pressure gauge

## Flow from pressure gauge

(OP)

For the following system. Water is pumped to atmosphiric tank and there is pressure gauge at the end of the line in a location is very close to pipe exit. Can we use this reading and with pipe diameter to calculate flowrate? By Crane it is suggested to consider k=1 and use velocity head to find flowrate . But i think results is over than actual and i think there will be factor for exit loss.

Any ideas???

Any ideas???

## RE: Flow from pressure gauge

Good luck,

Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

## RE: Flow from pressure gauge

h we can get from P at the line end

What is the wrong of applying that.?

I think there is somthing missing or factor to be used.

## RE: Flow from pressure gauge

## RE: Flow from pressure gauge

The point i want to confirm is there factor or not instead of 1

## RE: Flow from pressure gauge

Guage pressure = rho. g. h for an atmospheric tank

dP/dt = rho. g. dh/dt

Flowrate = F = tank csa . dh/dt

so

dP/dt = rho. g. F/tank csa

or

F= (dP/dt).tank csa/(rho.g)

Here, dP/dt is the rate of press rise at the base of this tank with time. The smaller the full scale range of the PG, the better.

## RE: Flow from pressure gauge

Measure dP at a constant flow rate (constant dP) over a given time. Measure the volume increase in your tank. Repeat at some different flow rates

Best regards, Morten

## RE: Flow from pressure gauge

Sorry i didn't explain the system in begining clearly.

In summary what i want to confirm, if only one reading of P is known and because it is atmospheric then P2 also known ( 0 barg).

Then this P equal v^2/2g multiply by some K.

Here to consider K=1 or there is another factor to use.?

Thanks for any idea

## RE: Flow from pressure gauge

you have a pump curve (pressure vs. flow),

at pumpu discharge there is a short pipe (you know fluid, diameter and lenght then you can calculate dp vs. flow) and finally a static head (h inside tank),

for pump, p out = dp (pipe) + static head (measured by instrument, assuming pipe horizontal, no dH)

to estimate flow from pump curve you need to calculate dp across pipe (could be a table of values)

to estimate flow from pressure loss at end of pipe there are several formulations but probably the simple solution is to create a table of values as already suggested by others

## RE: Flow from pressure gauge

## RE: Flow from pressure gauge

of course you should start from Bernoulli and difference (measured p vs. static p which is that of your instrument when flow = 0 or may be estimated from H and density as suggested by georgeverghese)...

there are many different methods (including differentials across plates, bends etc.) to estimate flow in piping, you may consider alternatives.

## RE: Flow from pressure gauge

BTW, I'm assuming this line connect near the bottom rather than the top of the tank.