Water Pressure and Flow Rate

[ElpacRovi]

Yes, I agree that they are not the same thing but together with pipe diameter they are linked. But, in all postings I have seen on this subject I cannot see that the link has been evaluated.

If I want to fit an instant water heater unit we have three variables ... volts (pressure), amps (flow) and wire used (pipe) and we have tables we can refer to. Why can we not have tables for water pressure/flow/pipe?

For example ... if I have water pressure of P1 and an open pipe of diameter D1 I will get a flow of F1 if I increase the pressure to P2 the flow will increase to F2 or if I reduce the pipe diameter to D2 but keep the pressure the same at P1 the flow will reduce to F3. If I put a tap on the pipe with a restricting flow it will further reduce the flow rate. It seems to me that it wouldn't take too much research to produce a set of tables that would show the flow rates for water through pipes of various diameters at various pressures with an adjustment (probably as a percentage) for fitting a tap of certain restriction. Yes, in a 3 decimal place world the temperature would affect the flow rate as would the length of pipe but not significantly so in a normal situation!

Does anyone know of any such tables?

David

 

[oldbuffer]

http://yorkshirecopper.com/wp-content/uploads/Technical-Guide-full-issue-02_14_Really2.pdf

 

[ElpacRovi]

Thanks oldbuffer but having looked at the page I'm not sure it's giving me what I want or maybe it's so complicated I can't find it! What I'm saying is if I have 1 bar pressure and a 15mm pipe I can fill a 25 litre container in X minutes and if I have the same pipe with 2 bar pressure I can fill it in Y seconds ... where can I find out how many minutes X and Y are?

 

[oldbuffer]

You can have a stab at it by using the nomogram on page 4.2, and assuming that the pressure loss is total between the source and your "open bucket".

As far as I'm aware there are no simple tables, because the flow rate depends on the pressure drop, which in turn depends on speed and pipe diameter. There are various formulae which can be used, but these also vary depending on whether the flow through the pipe is laminar (smooth) or turbulent.