I am using a 1HP pump to move water from a ground tank to overhead tanks that are at 30 feet height. The pipe is 1 inch.

Motor is currently exposed and open and I would like to know if I can move the motor to second floor at 20 feet height, where it will be protected from elements?

So the pump will be drawing water from tank that will be about 25 feet below and delivering water that is about 10 feet above.

  • $\begingroup$ Do you need the pump to be self-priming, i.e. to be able to pull a vacuum of air strong enough to lift the initial water up to the pump? $\endgroup$ Jan 11, 2018 at 10:02

3 Answers 3


The maximum water suction height is 33.9 ft ie: 10.3 m in perfect conditions.
Considering losses and pump efficiency you "could" get water to the pump level but I don't think you'd be able to pump it up 10 more feet.

  • $\begingroup$ Good answer, but it does require that the pump can draw or suck - it may not work as well as it does in a push situation... $\endgroup$
    – Solar Mike
    Jan 11, 2018 at 8:47
  • $\begingroup$ @SolarMike Suction needs the water column to be filled up to the pump. You can manually close the valve at the outlet of the tank and fill the pipes with water then start the pump then open the valve. This would create a water column that can be sucked by the pump. (You can install non-return valve on the tank to preserve the water column leading to the pump so you don't have to refill the pipes manually every time the pump is turned off and on again) unless "[The pump is] able to pull a vacuum of air strong enough to lift the initial water up to the pump" as Jonathan said in a comment on OP $\endgroup$ Jan 11, 2018 at 12:34

You need to consider net positive suction head, or NPSH. Wikipedia article here. This is typically influenced by pump height, water temperature (vapour pressure) and friction losses. The higher you lift you pump w.r.t. your fluid source, the less NPSH you'll have available. Increasing fluid temperature and lengthening the suction pipe will have a negative impact on NPSH available.

In order for pumps to work properly, you require a minimum amount of NPSH, which you can get from your pump's datasheet. This is typically influenced by the pump type, operating pressure and flow rate.

If you have less NPSH available than required, cavitation will happen which will decrease pumping efficiency and damage the impeller.

Doing a very rough, quick calc puts your NPSH available at around 2m. I don't have much experience with typical pump NPSH required curves but I don't recall typical values much lower than 2.5m, so I think your pump will have a hard time pumping.

Here is a link to a sample calculation which is a bit simpler than the Wikipedia examples. Pay close attention to consider the lowest liquid level you'll be required to pump in order to be conservative.


Depending on the type of pump, you'll have to prime it, i.e. you have to fill the suction pipe with water every time before you start the pump because the pump cannot form a vacuum with air to draw the water up, so it will run dry and burn out the pump.

  • 1
    $\begingroup$ Restated : every significant pump has a performance rating based on the NPSH. The lower the NPSH the lower the pump performance ,\; or , the higher the pump the lower its flow. $\endgroup$ Jan 11, 2018 at 16:30

Water (any fluid) has a maximum suction height.

What happens is the the water boils.

Even at 70 F water will evaporate and has a vapor pressure of 0.0231 ATM.
Water will boil at 70 F and 0.0231 ATM.

The pressure of a liquid column is density * height
the density or water is 62.428 lb/ft3
1 atm is 14.69595 lbs / sq inch = 2116.2168 lbs/ft2
can just use zero for vapor pressure of water in the equation
62.428 * height = 2116.2168
height = 33.9 feet

A pump cannot produce a perfect suction. The realistic suction height is about 25 ft. So you are right on the edge.

A suction pump typically has a different design. It is more efficient to push a liquid than pull (suck) it.


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