# Pipe Pressure from discharge in Tank

1. Jan 20, 2012

### Juanka

The diagram attached is a picture of the problem I have. I have a 10ft tall cylindrical tank with 20ft of pipe directly under it. The tank at full capacity can hold 100 gallons of water or 10 gallons per ft. I want to calculate the pressure of the water right before it leaves the pipe 20ft below. The pipe is of 1" diameter. I know from fluid mechanics that pressure=rho*gravity*change in height. Is it important to apply the diameter of the pipe into the calculation or is it negligible?? Thank in advance!!

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2. Jan 20, 2012

### Juanka

Or is the following formula applicable?

Pressure= 14.7psi + [1.96 slug/ft^3*[30*(12)]in*[(32.2)*(12)]in/s^2]

3. Jan 20, 2012

### obafgkmrns

You're making it too difficult. The pressure is simply 14.7 psi. Think about what the pressure inside the stream is a fraction of an inch after leaving the pipe. The pressure in the stream a fraction of an inch before leaving the pipe must be the same.

The flow inside the pipe will adjust itself so that the head loss in the pipe equals the pressure at the bottom of the tank.

4. Jan 22, 2012

### firavia

bro I think the formula is applicable indeed, anyway if you want help in such fluid dynamics or static problem visit this webpage it explains it all : http://wwwfiravia.com/mecheng.html [Broken]

Last edited by a moderator: May 5, 2017
5. Jan 22, 2012

### obafgkmrns

Nope. It would be appropriate only if the lower end of the pipe were sealed and there were no flow. Because the flow is discharging freely into the atmosphere, the pressure at the bottom of the pipe is 1 atmosphere.

Last edited by a moderator: May 5, 2017