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Wednesday, August 31st 2016, 3:26pm

elevation drop over distance, psi & gpm relationship

i am installing a new irrigation system & well for a small-scale farm, running low-pressure overhead (25+ psi, 1.75+gpm). i can get 10-13gpm from my pump.

from the well-head to the mainline is 500ft, with 10 ft of elevation loss.
from the first lateral to the last is a maximum of 750 ft, with a 45ft elevation loss.

i am trying to decide on 1) buried line to run from well to farm fields, 2) farm mainline to run to laterals.
my experience is that 1.5" on the laterals works.
i was considering doing 1.5" on #1 & #2 (see two lines above), as the elevation drop would balance the pressure loss over distance ... enough.

however, i don't fully understand the relationship between pressure and flow-rate. do these balancing forces -- elevation loss & tube friction over distance -- only impact the pressure, and not the flow-rate?

if anyone has any suggestions on pipe size, or comments on my question, i'd appreciate it.

many thanks


Supreme Member

Posts: 5,288

Location: Metro NYC


Wednesday, August 31st 2016, 4:05pm

Elevation has nothing to do with flow rates. It merely adds or subtracts from pressure. You employ friction loss tables to determine the effect of pipe sizes on your system design.

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