
#1
May1113, 05:32 AM

P: 10

Dear All
My water tank fixed on roof top 5M from the ground Height of tank 1m width of tank .75m ( Cylinder type water tank ) if water out from the tank by .5 inch hose how can I measure the pressure at 1m height from the ground Please advice Thanks in advance 



#2
May1113, 06:05 AM

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P: 38,894

The pressure on a surface is the weight on that surface divided by the area. Since any fluid, like water, exerts the same pressure in all directions, to find the pressure at the end of a hose .5 inches in diameter, of height h, you could calculate the volume, [itex]\pi(.5)^2h[/itex], then multiply by the density (the density of water is 1000 kg per cubic m or 62.3 pounds per cubic foot) and finally divide by the area of the end of the hose, [itex]\pi (.5)^2[/itex]. Of course the "[itex]\pi (.5)^2[/itex]" terms will just cancel out, leaving "density times height". It seems odd that you give the diameter of the pipe in "inches" and the height in meters but, since only the height (5 1= 4 meters) is relevant, use 1000 kg per cubic meter (approximately) as the density of water. 



#3
May1113, 06:48 AM

P: 10

Thanks for the reply
Please also advice how measure the pressure when the thank water level going down Thanks in advance 



#4
May1113, 11:31 AM

Mentor
P: 7,292

Measuring pressure of water tank
Probably the best way is with a gauge.
It is hard to know the loses due to the hose. You know that the final pressure will be less then the ideal pressure given by ρgh. ρ is the density of water, g the acceleration due to gravity and h=4m. 



#5
May1313, 03:50 AM

P: 10

Could you please advice me according to my attached picture How may I calculate the pressure location of Letter "A" It could be much appreciated if you can sow me step by step Thanks 



#6
May1313, 08:27 AM

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The pressure is, as I said before, the total weight of the water above that point, divided by the area it is pressing against. Here, you have cylinder of water, 1 m in diameter, so .5 m in radius and 1 m high. That has volume [itex]\pi (.5)^2(1)= \pi/4= 0.7854 cubic meters. Water, at standard temperature and pressure, has a density of 1000 kg per cubic meter (that's essentially the definition of "kg") so that water has a mass of 785.4 kg and so a weight of (785.4)(9.81)= 7705 Newtons.
Your pipe is relatively so small the water in it adds only a very tiny amount to the weight of the water and can be ignored. However, the pipe has radius .5 inch so 1.25 cm= .0125 m and area [itex]\pi (.0125)^2[/itex]= 0.0004909[/itex] square meters. The pressure at A is 7705/.0004909= 15696497 Newtons per square meter. 



#7
May1313, 11:24 AM

P: 10

Thank you so much for details reply Can you please tell me where did you get the value ( 9.81) What is the meaning of (itex) Please advice 



#8
May2413, 09:40 PM

P: 10

I got 9.81 which Earth gravity and [itex] too. I should think you not consider water tank fixed from 5m from the ground in above calculation right? 



#9
May2513, 12:43 AM

HW Helper
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P: 5,578

I'm sorry, but the calculations for pressure at point A have taken a weird turn. According to Halls of Ivy, the pressure at point A is some 15.7 MPa, which is in excess of 2200 psi, or more than 150 atmospheres, all produced by a column of water 4 meters tall.
According to Pascal's law, the static pressure in the hose at point A is the fluid head or 4 meters of water. This is equivalent to a pressure of: rho*g*h = 1000 kg/m^3 * 9.81 m/s^2 * 4 m = 39,240 N/m^2 = 39.24 kPa = 5.69 psi which a hose or pipe should be able to withstand without blowing up and killing everyone standing nearby. Remember, all of the water in the tank is not pressing on the hose at point A, just the column of water immediately above the point A in the hose and the tank itself. 



#10
May2513, 03:27 AM

P: 10

Actually my pressure measuring sensor measuring range is 1 to 100 kPa http://www.freescale.com/files/senso...et/MPX5100.pdf As per SteamKing I can implement the my project which is displaying water level in the LCD display Please advice 



#11
Jun113, 08:43 AM

P: 754

The easy answer is:
231' of water (measured vertically) creates 100 psi, no matter what the shape of the hose or tank. (Or, more simply, 2.31' of water equals 1 psi). So, if your tank is half full (filled to the 0.5m level), that would mean that at 1m from the ground, you'd have a vertical measurement of 4.5m of water (4 meters up to the bottom of the tank, plus 0.5m to the surface of the water). 4.5m is approximately 177.165 inches. 177.165 divided by 2.31 equals roughly 76.69 psi. So, simply measure the height of the water in the tank in meters (0m to 1m), add 4 meters, and divide by 2.31 to get the psi at a point 1m above the ground. Of course if the tank is empty, you would simply measure the vertical height of the water in the hose alone (0m to 4m). 


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