pressure drop along a pipe

[lelehaine]

Hello, i have a theoretical question:

Let's say i have a tap served by a pipe running horizontally for 50 meters. The pipe is served by the main water line through a ball valve. Both the pipe and the ball valve are 15mm in diameter.
As far as i know, there's a constant pressure drop along the pipe, related to its diameter.
I would like to know if replacing the pipe with a 22mm one, while maintaining the ball valve and tap, would make any sense in trying to reduce the pressure drop.
In other words, do the ball valve and tap are the bottle neck for the water flow rate, regardless of the connecting pipe diameter?

I hope it makes sense to you, sorry for not being a native english speaker!

Thanks!!!

 

[kirkgas]

When you say ball valve do you mean in a tank, I know you are saying mains fed but ball valve to me is the fitting that fills a storage tank or cistern, so I'm confused, but either way if you have a constant pressure entering the pipe you must get less of a drop in the bigger pipe, for a short time anyway, if there's no flow and the pipe is full when you open the tap you will get more water out, if the mains pressure is quite low it will start to loose flow
But I'm watching man city game and it's nearly getting exciting in the last 10 mins so can't think it all through

 

[lelehaine]

Hi, sorry about that, i thought about a ball valve just to mention a part of the circuit with a fixed diameter (Here we use ball valves to split a line in sub lines for servicing purpose).
Here is another example: i have the main line, then 1 meter of 15mm pipe, then a tap (name it tap A), then 50 meters of the same pipe and then another tap (tap B). In these conditons, based on my knowledge, i would expect to have a lower flow rate from tap B, compared to tap A. My goal is to maintain the flow rate of tap B as similar as possible to tap A. So if it would take 1 minute to fill a 20 liters sink from tap A, i would like to have a similar situation from tap B. Would a larger diameter of the 50 meters pipe help?

 

[Dotty]

Benvenuti nel UKPF

Yes it would. You've pretty much answered your own question il mio amico

 

[lelehaine]

Benvenuti nel UKPF

Hello croppie, thanks for answering. How did you know i'm for the bel paese?

Due to the recent political news, i was rather trying to hide my origin... but you got me! :wink_smile:

 

[Dotty]

We mods have special powers! Your English is fantastic, far better than my Italian!

 

[Gas]

Bernoulli law is what you are looking for

 

[lelehaine]

Your English is fantastic,far better than my Italian!

Haha great! Thanks! Anyways your Latin is far better than mine, which i'm supposed to have studied for 5 years at school!

Bernoulli law is what you are looking for

Yeah i know... you are right, but as for latin... i'm not so good in things you study at school...

 

[Jimbob]

Larger the pipe, the less the pressure drop. Many people assume that because you have a smaller bore valve - the bore determine the pipe sizing and there is no point going up a size. Doesn't work like that though

 

[chris watkins]

 

[chris watkins]

woop's sorry for large pic but this is the kind of image I use to try to explain what happens to pressure & flow rates within a dynamic plumbing system. if you add a valve the friction increase will cause a loss in available head (pressure) down the line.
Can you give us a be more info on pipe used & amounts of water required at A&B, as well as water pressure (head) at the beginning of the run.
If you need to maintain equal flow rates from A&B why not fit flow restrictor's to each of the outlets?

 

[lelehaine]

Many people assume that because you have a smaller bore valve - the bore determine the pipe sizing and there is no point going up a size. Doesn't work like that though

Thanks, that's exactly what i was trying to figure out! I asked my plumber if i would have advantages by replacing the pipes with larger ones, he said no because of the initial an final fittings, but i thought he was wrong.

Chris, thanks for the pic, now it makes perfect sense to me!
So, using a larger pipe would result in this, right?

Can you give us a be more info on pipe used & amounts of water required at A&B, as well as water pressure (head) at the beginning of the run

It was just an example, no real A&B taps and equal flow rates needed, it was just a simple model to analyse.
I'm renovating my apartment, adding a second bathroom, moving the boiler in the balcony, the kitchen is located on the opposite side of the balcony and the main line is located at the center of the apartment, so i will have many pipes going forth and back, with many elbows. It's on the 7th floor of 8, i don't know the main pressure (but i guess it is 2.5 bars or something like that) it comes from a 1/2" line (i can't modify this line) and all the pipes and fittings in the apartment are actually 1/2". My idea is to use 3/4" in the apartment to mantain adequate flow rate.

 

[Dotty]

Larger the pipe, the less the pressure drop. Many people assume that because you have a smaller bore valve - the bore determine the pipe sizing and there is no point going up a size. Doesn't work like that though

It's flow rate he wants to maintain, not pressure as we know it Jim

(couldn't resist it!)

 

[SimonG]

.......Star Trekkin across the universe, always going forward, still can't find reverse...........

 

[Dotty]

**snigger**

 

[SimonG]

apologies for digressing Might have to go on the jukebox tonight

 

[chris watkins]

Thanks, that's exactly what i was trying to figure out! I asked my plumber if i would have advantages by replacing the pipes with larger ones, he said no because of the initial an final fittings, but i thought he was wrong.

Chris, thanks for the pic, now it makes perfect sense to me!
So, using a larger pipe would result in this, right?
View attachment 15118



It was just an example, no real A&B taps and equal flow rates needed, it was just a simple model to analyse.
I'm renovating my apartment, adding a second bathroom, moving the boiler in the balcony, the kitchen is located on the opposite side of the balcony and the main line is located at the center of the apartment, so i will have many pipes going forth and back, with many elbows. It's on the 7th floor of 8, i don't know the main pressure (but i guess it is 2.5 bars or something like that) it comes from a 1/2" line (i can't modify this line) and all the pipes and fittings in the apartment are actually 1/2". My idea is to use 3/4" in the apartment to mantain adequate flow rate.

The changes in the direction of flow will have a much greater effect than the actual friction created along a straight run, at a dynamic pressure of say 1 - 1.5 bar in a flat not a lot would be gained by increasing the size of the supply if the mains was only 1/2". Try to minimise the elbows, use long bends or plastic pipe etc.