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How to convert Gallons Per Hour to PSI?

  1. Mar 19, 2015 #1
    Hey all im a newbi and wondering how to do this conversion. When i see a water pump which is 1400G/hour at that rate what would be the psi?

    For example my garden hose is about 40psi and at that rate it would mean a curtain g/ph based on say a 15mm outlet radius.

    Im trying to figure out what pump i need for my water fall feature for my pond, but as a the filter needs to sit bellow the pond i will need extra power for the water to travel up about 600mm and feed into a 300mm spillway, so i was trying to do a experiment with my garden hose and time to see how long it takes to fill say 2 gallons, based on a 40psi and 15mm outlet and 600mm hose held up 600mm high from the ground to see what sort of water flow i get so i can have an idea what sort of pump i need.

    the pump im looking at is 530g/h with power of 55W with 19mm outlet
    Last edited: Mar 19, 2015
  2. jcsd
  3. Mar 19, 2015 #2


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    Staff: Mentor

    Welcome to PF!

    Pressure and flow are related somewhat by Bernoulli's equation, but moreso on the details of the system. If the lift you need is 900mm, you can convert that to pressure easily enough by multiplying by the weight density of water. But as often as not, the pressure is actually expressed as the lift distance (head).

    You can google for performance data/curves for landscaping waterfall pumps. There are lots and they are in the range that is typical for the application. They will say in the catalog information what the flow rate and pressure is....though you have to be a bit careful about that. Performance is a curve and the flow and pressure listed are often on opposite sides of the curve. You need to look specifically for the performance data.

    Also, the wattage will depend on the flow and pressure.
    Last edited: Mar 20, 2015
  4. Mar 20, 2015 #3


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    It's possible that the 530g/h figure is the maximum flow rate at zero pressure. It will have different flow rate at different pressure. See if there is a graph of pressure v flow rate for that pump.

    To work out the pressure you need... First you need enough pressure to raise the water the height required. That's about 0.43psi per foot. So to raise water 3 foot you need at least 3*0.43 = 1.29 psi. However to that you also need to add the pressure lost in the hose/pipe and any filters.

    This site shows that at 530g/h (=8.8g/min) the pressure loss down a 3/4" (19mm hose) is about 10psi/100ft or 1psi/10ft.

    As for the loss in a filter you would have to estimate or ask the manufacture?

    Add up the above to get the total pressure needed. Add some contingency for blocked filter or squashed pipe and you will get the total pressure required.

    Then you need to look at pump data and pick a pump that can deliver the required flow rate at the calculated pressure. You want one that can do this comfortably (eg middle of the recommended range not one end). Some manufacturers might also give you efficiency curves or "safe operating area" data to help select the right pump.
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