Does reducing the water pipe diameter increase pressure?

[macgee]

Firstly, I do understand that we can't increase the dynamic (working) pressure from the incoming main without introducing a pump or increasing the main pipe itself.
The reason I ask is because I keep thinking of the hose pipe scenario where if you pressurise the end with your finger you then increase the velocity of the water. Is this just because this is at the point of exit or does it also apply within pipe work over short runs. I understand the longer the run, the more pressure loss but over short runs, DOES REDUCING THE PIPE AND THEREFORE THE FLOW, INCREASE TO GIVE YOU THE MAXIMUM WORKING PRESSURE YOU CAN ACHIEVE.

Sorry if that's confusing?

Thanks.

 

[DaleRCL]

No, it doesn't.

 

[GasBod]

By having your thumb over the end of the hose you are increasing dynamic pressure by restricting flow.But you haven’t created any NEW pressure. You have simply traded reduced flow for increased pressure

 

[macgee]

GasBod wrote:-
By having your thumb over the end of the hose you are increasing dynamic pressure by restricting flow.But you haven’t created any NEW pressure. You have simply traded reduced flow for increased pressure

So does this mean that following the same theory, that if you branch off a 15mm tee with a 10mm pipe, you will have the same principle at the end of the short 10mm run. Reduced flow for increased pressure. Or is the pressure the same if you were to run the same branch in 15mm.

I know that your not creating new pressure but does it mean your achieving the highest dynamic pressure you can given your incoming supply.

Thanks.

 

[TicklyT]

It may sound counter-intuitive, but reducing the pipe diameter decreases the pressure in the smaller pipe. That's Bernouii's principle in operation. http://en.wikipedia.org/wiki/Bernoulli's_principle

To maintain a given throughput, the velocity in the smaller pipe must be greater, and, according to Newton's laws, the only way to increase the velocity of the flow is for the pressure in the smaller pipe to be lower.

It's the same principle that makes, among other things, carburettors work, aeroplanes fly and Giffard injectors do their thing.