Pressure in different pipe diameter

[SuperBadGrower]

I've been wondering about this, trying to figure it out. Bernoulli's principle and stuff.



According to bernoullis principle PSI should be the same at points A& B, unless I am mistaken




Then why aren't irrigation systems made like this, using small pipe where possible, and big pipe were needed?


(the angled lines are to indicate "long distance")

Especially in a lawn where you may have large distances it seems like it would save money. Am I looking at it the wrong way?

edit: Yeah I think I'm seeing it the wrong way. You probably lose more pressure over a long distance of small diameter pipe than you would if you used the same size pipe.

 

[chacaldubengale]

more the hose is small more load losses you will have .. 1/2 is good for small setup
if you want homogeneous watering for each plant then you need Pressure compensative drippers .. and a pump enough strong to power them

 

[SuperBadGrower]

Welcome! Indeed, you are right. Luckily I have all that working already, I was really just curious what happens after a reduction and then an increase back to normal.

 

[Teddybrae]

Such a RESTRICTION will effect VOLUME not PRESSURE ... amount of flow not pressure of flow ...

 

[SuperBadGrower]

Such a RESTRICTION will effect VOLUME not PRESSURE ... amount of flow not pressure of flow ...

Do you mean, the volume/flow is affected at point B, or at the restriction? Cheers

 

[I'mback]

Do you mean, the volume/flow is affected at point B, or at the restriction? Cheers

Pic 1 is all wrong good buddy. Read left to right:
High Pressure, High Velocity, Low Pressure to operating pressure
High Volume, Low Volume, Low volume

The pressure points are normally at the throat (reduction) of the pipe. If you go for a 1" supply pipe to a 1/2" restriction, we can theoretically say the the flow has been reduced by 50%. Eventually if you dead head the side after the restriction, eventually the pressure will equalize across the restriction. Because you are going through a restriction, pressure will build up at the inlet because the design of the system requires a 1" pipe in order to deliver 30gpm. It can't! As pressure builds up, it is trying to put 10# of Poo in a 5# bucket. It ain't going to happen, so velocity increases through the restriction. At the outlet side of the restriction, the pressure will be lower as the volume of the area increases (1" pipe). Pressure willo equalize both sides of the restriction, eventually but, the capacity of the outlet side has been reduced/throttled by 50% thus, only having a capacity of 15 gpm. That is why in modern homes you have a 3/4" supply (some 1") with 1/2" take offs to whatever your needs are. If you are in the shower, and someone opens a cold tap in the bathromm downstairs, you don't get scolded because their is a 50% capacity in reserve.

 

[SuperBadGrower]

it is trying to put 10# of Poo in a 5# bucket. It ain't going to happen,

I had to read it 3 times because this part had me laughing every time

Pic 1 is all wrong good buddy. Read left to right:
High Pressure, High Velocity, Low Pressure to operating pressure
High Volume, Low Volume, Low volume

The pressure points are normally at the throat (reduction) of the pipe. If you go for a 1" supply pipe to a 1/2" restriction, we can theoretically say the the flow has been reduced by 50%. Eventually if you dead head the side after the restriction, eventually the pressure will equalize across the restriction. Because you are going through a restriction, pressure will build up at the inlet because the design of the system requires a 1" pipe in order to deliver 30gpm. It can't! As pressure builds up, it is trying to put 10# of Poo in a 5# bucket. It ain't going to happen, so velocity increases through the restriction. At the outlet side of the restriction, the pressure will be lower as the volume of the area increases (1" pipe). Pressure willo equalize both sides of the restriction, eventually but, the capacity of the outlet side has been reduced/throttled by 50% thus, only having a capacity of 15 gpm. That is why in modern homes you have a 3/4" supply (some 1") with 1/2" take offs to whatever your needs are. If you are in the shower, and someone opens a cold tap in the bathromm downstairs, you don't get scolded because their is a 50% capacity in reserve.

Thanks a lot man, I really understood that elucidation. it has cleared up my confusion.

 

[I'mback]

U R welcome Sir