Which position of the water pump in the below diagram provide maximum water output to the overhead tank?

enter image description here

  • Each floor is 12 feet in height.
  • I already have the pump (Centrifugal Regenerative Self Priming 1HP Peripheral Type, Self Priming - 180sec At 3m STATIC SUCTION LIFT) and would like to know which is the best location to install it for maximum water intake to the overhead tank. The water Supply is only available for a limited period everyday and the goal is to achieve maximum water to the overhead tank.
  • The Water supply line provides water from a bigger (8inch) main line but water pressure from it is not adequate to pump up water on top level. (Water pressure only enough to supply water to first floor and that too with reduced pressure.)
  • The water pipe from main supply to pump and from pump to overhead tank is 1/2 inches wide.
  • 2
    $\begingroup$ You will need to provide more information. An annotated sketch with all the levels is needed. Also, the pressure of the supply line at the valve. Also, do you want to compare identical pumps? Situation B will most likely require a differently designed pump than A. $\endgroup$
    – SlydeRule
    Commented Apr 30, 2016 at 6:15
  • $\begingroup$ 760mm of mercury corresponds to 10.3 meters (34 feet) of water. With only a pump at the top, you can't raise the water more than roughly 34 feet above the height where the pressure of the water supply gives out. What's the pressure delivered to the left side of that valve on the supply? Also, there are pressure drops due to motion, needs more info on the pipes and flow rate (unless you mean in the limit of zero flow rate of course!). $\endgroup$
    – uhoh
    Commented Apr 30, 2016 at 8:02
  • $\begingroup$ I have added new information to the question as requested. $\endgroup$
    – user343272
    Commented Apr 30, 2016 at 12:13

4 Answers 4


Your main aim is to draw more water in short time.

The flow rate through a system such as yours is a balance between the pumps abilities (head curve) and system friction loss (which increases with flow rate). To increase the flow rate - reduce system losses - replace pipelines with those of large diameter (say 1 inch).

The location of the pump does not influence the flow rate - as long as adequate suction pressure is available. To ensure the later, keeping the pump at the bottom is better (as discussed in other answers)

But if you want to raise the water higher with a single pump, then consider keeping it on the top (provided the pressure in main line is sufficient to provide the list 14.7 psi = 10.33 m (34 ft) of lift)


Think about the pressures. With the pump above the supply line, the pressure at the input of the pump will be lower than the supply. At roughly 2 PSI per foot, you're down about 18 PSI.

Since air pressure is about 15 PSI, the system will at least work as long as the supply pressure is over 3 PSI, but that's still not a good situation. If the "supply" is a open pool, then it won't work at all since even a full vacuum can't get the water that high.

With low input pressure, the pump will be more prone to cavitation. That's bad for the mechanics and a waste of energy.

Therefore, put the pump at the bottom, not the top.

  • $\begingroup$ So you mean to say I must use the pump at ground floor for maximum water to the tank from the supply line? I am using the pump at the roof as of now and it is able to suck water - Just wanted to know if using it on the ground floor makes any difference to the amount of water we can suck from the supply line. Also, will using thicker 1 inch pipe after pump (the input will remain 1/2 inch) make any difference? $\endgroup$
    – user343272
    Commented Apr 30, 2016 at 14:48

Considering this is a centrifugal water pump, it can provide very little air suction. That means if your pump is airlocked, there's not a shade of a chance it will be able to produce nearly enough suction to pull the water up two floors. And it will be airlocked all the time.

With a check valve preventing backflow into the mains, and then filling the water lines and the pump with a bucket, you might have chance to get the 'top pump' config started... until it gets airlocked one way or another again.

The "low pump" config will get enough mains pressure to fill the pump with water and then the pump will have no trouble handling the height.


In worst condition when pump are installed on top it cause cavitation in which affect both performance of pump and discharge also pump have to work more in this condition thus more consumption of electricity. In your given situation there no such problem of cavitation it happen in worst condition but by the same means it affect performance and discharge of your pumb

Let it's understand by a life example of you are not a technical person then also you can easily understand this... Suppose you have to drink, soft drink using straw for this you have to suck with your mouth by applying some negative pressure from your mouth and you achieve this easily, now in situation second you are on fifth floor and bottle is on ground floor you have to suck the drink with your mouth via a long length straw now it is next to impossible because suction need more vaccum pressure in reverse of this if you have to blow some drink from full bottle by applying blow of air from your mouth it is quite easier than sucking it to mouth

In same manner bump have to do more work on water to suck this from sump than it pushes to top There is another problem also if you apply that much of work on water to suck up to high head the water absorb that much amount of energy and start converting in vapour and forming of bubbles happen now you pump pumping bubbles that means very less amount of water only air and air (technically called cavitation and due to bubbles formation life of pump will suffer and discharge goes down)


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