Problem with pressure

  • #1

Main Question or Discussion Point

Good morning brothers,
I am a new member and I need your help . Really I did not know about this valuable web site. It’s really amazing.
I am working in water section. I had a problem with pressure. I hope you could help me to solve it out.
I have reservoir of fresh water which distributes the water for the all the building network. But last month I had a problem that water is not reaching to one of the building which is about 30 meters tall. My question is how much pressure is required to push water to the overhead tank in same building. Note we are using gravity only no pump in the network.
Pressure : Bar / PSI ??? , Carrier pipe HDPE : 2 “
Distance from Reservior to building : 600 m
Building height : 35 m
 

Answers and Replies

  • #2
2,685
20
If you are using gravity only, then you need to make sure the reservoir is higher than the outlet. It's as simple as that.

Also, the more pipe there is the higher the reservoir must be above the outlet.
 
  • #3
tiny-tim
Science Advisor
Homework Helper
25,832
250
Welcome to PF!

Good morning Ibrahim! Welcome to PF! :wink:

Yes, nothing matters except that the surface of the water in the reservoir has to be higher than the outlet in the distant building. :smile:
 
  • #4
thx bro, the problem that i want to calculate how much exactly the water pressure to carry out to the top of building . The reservior is in a high place but its little farer from the building. Its bout 600 m from the building. when i fit the pressure gauge in the nearest point before the building , the gauge was showing 3 bars. but water is not reaching in the top of the building.
 
  • #5
1,384
0
What is the exact height of the water tank from the reservoir?
If the water tank is higher, then you have to use a pump. Gravity alone cannot create the required pressure.
 
  • #6
2,685
20
A rough calculation:

Mass of water in the pipe = ALm = (pi*0.025442)(35)(1000) = 71.16kg.

Where A = area of pipe = pi*r2, L = length of pipe, m = mass of water per cubic metre = 1000kg/m3.

So if we ignore the height of the pipe for the moment:

(71.16)(9.81)/(pi*0.025442) = ~343337.2N/m2 = ~49.8 PSI

3 Bar = ~43.5 PSI

As you can see, even the minimum pressure at the bottom of the pipe is greater than the pressure from the reservoir.

It's a simplistic review, but it highlights the problem you are having.
 
  • #7
5,601
39
Are you saying the water previously made it to the top of the building to fill the tank withut a pump, but no longer does? If so, a drop in the water level of the reservoir or a blockage in the piping somewhere is likely the problem.

As noted above, if the water tank is 30 meters tall, then the water level in the reservoir must be higher from the same reference level so that water will flow "downhill" and fill the tank without a pump. The higher the reservoir water level, the faster the water will flow.
 
  • #8
RonL
Gold Member
1,097
215
Look for any portion of the system that relies on a siphon effect to pull water over a high point, if there is one and air was admitted, it will need to be purged.

Ron
 
  • #9
2,685
20
Well first, I'd consider my rather basic calculation above. It shows that the water from the reservoir arriving at the bottom of the building at 3 Bar isn't enough to get to the top.

The OP has not said water ever reached the top of the building and so it looks like they've built something too high for the supply system in place without using pumps.
 
  • #10
Exactly, we found that meter unit is blocked cos the meter number wheels are not rotating and water is not passing freely.

Your conclusion is right about our system . The only question here that sometimes we need to know the pressure required to take the water till the top of the builing. Once we connecta pressure indicator we could get the result at once.





Are you saying the water previously made it to the top of the building to fill the tank withut a pump, but no longer does? If so, a drop in the water level of the reservoir or a blockage in the piping somewhere is likely the problem.

As noted above, if the water tank is 30 meters tall, then the water level in the reservoir must be higher from the same reference level so that water will flow "downhill" and fill the tank without a pump. The higher the reservoir water level, the faster the water will flow.
 

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