Pressure question

[arty21]

Hi all.

Can anyone lead me in the right direction to answering this question?

A cold water pipe has a tap attached over a sink. The standing pressure in the pipe is 3 bar average. When the tap is open the pressure decreases to, say, 1 bar. When the tap is closed suddenly does the pressure increase to above the standing pressure or does it return to 3 bar?

I know its a silly question but my appresntice asked the question and its a long time since I took my c&g and cant remember the answer.

Thanks for the help

Arty21

 

[Puddle]

Well we have a pressure and flow situation here
The answer is not straight forward as you would expect from an apprentice
You have two options to this question
1.You can clip him around the ear and tell him not to be so impertinent, asking silly questions
Or
2. Explain it depends on speed of flow, presure and how fast you turn the tap off
If you have standing pressure of 3 bar that is the pressure that will be in the pipework when tap turned off after any effect of turning the tap off fast has been dispersed
Will or could the pressure go above the standing pressure if tap turned off
Yes it could
But, if it will or by how much depends on what pressure is present when tap is closed, what speed the tap is closed, at what speed it is flowing and the surface area of the tap washer on the tap
Basically, you have the pressure of the water flowing through the tap but that pressure will be increased by the speed/force the water is travelling through the tap when closed
As the force pushing the water through, if stopped suddenly, has to go somewhere and it is transferred into pressure
Then there is how quick the tap is closed, the quicker closed, the more of the flow force can be converted to pressure in the water
Then there is surface area of washer to absorb any of the flow pressure
Then send him away to find the calculations involved, whilst making you a nice tea,
as he should be doing in the first place

 

[newbie1]

tell him to bugger off and do something usefull he sounds far to clever to argue with

 

[Bernie2]

Hmm!

Explain water hammer to him!

 

[justlead1]

Hi Suggest he looks at the "hydraulic ram" for guidance. Is a device that allow water to be raised above the level from which it come. The energy that allows this comes from the water its self, no other energy required.