Question on hydrostatic pressure (leak test) 2

[eddtan]

Hi,

I have a 12(W)x18(L)x1m concrete tank installed underground and it will be subjected to pressure of 0.5bar.

To test the tank for leaks, instead of pressurizing the tank using pumps or air blower, my supplier suggests we use a 1 inch hose with 1 end connected to the top of the tank (completely filled with water), and connect the other end to an elevated IBC 10m above the top of the tank.

He claims that this way the tank will be subjected to pressure of >0.5bar and <1 bar.

What do you guys think? I mean it sounds logical because he is trying to create the pressure using hydrostatic pressure. But is this 10m water column in the small 1 inch hose able to provide the sufficient pressure to test the huge 12x18x1m tank? If the tank is completely filled with water, there will be no flow, and Bernoulli equation would dictate headloss=0 and the static pressure in the tank would be 10m?

Back then in school the examples given were otherwise. The tank providing the hydrostatic pressure would be huge, while the receiving end at the bottom are pipes. I can fully understand this part taught in school. But to put it the other way round with huge tank at the bottom and pipes providing the hydrostatic pressure, I cannot reconcile.

Am I missing something? Advice please? Thank you so much.

 

[LittleInch]

It sound logical because it is.

You get pressure but what you don't get is much volume or energy that you get from a larger tank, but in this case you don't need to.

10m is very close to 1 barg so seems a bit high for a tank only designed for 0.5 barg

Remember - More details = better answers
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[SlideRuleEra]

Static hydraulic pressure for given conditions is dependent on one, and only one variable, depth. Size, shape, horizontal distance do not matter. In the sketch shown below, static hydraulic pressure at any chosen elevation is exactly the same for all cases... this applies for the examples you describe from school, also. Sometimes intuition is just plain wrong, this is one of those times - go with the math.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[Ron]

@SRE.....Amen.

 

[Compositepro]

This concept should be intuitive to any engineer.

 

[LittleInch]

I know we're talking water here but strictly the pressure is dependant on height AND density of the fluid.

Pressure of 10m of water is higher than 10m of gasoline.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Spartan5]

Just bear in mind that the loss of as little as 1 pint of water will cause your water level in the hose to drop 3 feet. So make sure every connection is watertight. Even greater of a concern would be that the tank is 100% purged of air.PV=nRT, diffusion, etc. of the smallest pocket of air will play hell with your results.

 

[robyengIT]

furthermore, before test, you must allow absorption of water by concrete (at least for 12 hours) at a pressure bigger than the test pressure : if you don't do so, absorption will continue and pressure will drop (similar to a leakage : this is very clear during test of concrete pressure pipes)