Paul wrote:

Correct me if I am doing this wrong.

Russell Kent wrote:

Always.  :-)

Since most pumps are rated in head measured in feet of lift one cubic foot of
water weighs 62.43 pounds

Correct. (one cubic foot of water = 28.3 liters, which is 28.3 kgs, which is 62.43
lbs)

so that would be 62.43 pounds/144 square inches of area  or .433 psi.

Correct.

50 foot of water would then be about  22 psi.

Correct and easily testable.  A pump cannot "suck" water higher than 33 feet
because there is only one atmosphere (14.7 psi) to work with.
33/14.7 = 2.24        50/22 = 2.27
Close enough.

Looking at the page in MaxMaster Carr the 3/4 HP pump is
pumping 35 gallons per minute at 10 feet or 4.3 psi.
It pumps only 20 gpm at 13 psi.
It cavitats at a back pressure of only 14 psi.
What Macmaster Carr calls "shutoff".

The one HP pump in the group looks more typical of an automotive pump.

These pump are probably more efficient than automotive pumps as they are larger
and are rotating at about half the RPM so seal friction HP would be less.

Paul Lamar

Thanks Russell. (I think :-))

Paul Lamar

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