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That was a pretty good video.
To add to it:
Once you know the pump impeller diameter, with the system back in normal operation, plot the dp on the impellor curve and read the GPM.

Without going deadhead you could simply thread a 1/4" vacuum gauge into the suction side of your pump strainer and note inches of mercury. That X1.13 will give you suction side head loss. The pressure side gauge psi X 2.31 will give you return side head loss. The sum of these applied to your pump curve will give you flow rate in GPM.

CALCULATE TDH - Multiple the Vacuum gauge reading x 1.13. Multiply the Pressure gauge reading x 2.31. Add the two products together to determine TDH for your system. Our readings were 15 and 23 respectively So (15 x 1.13) + (23 x 2.31) = 17 + 53 or 70 TDH.

If a typical pool system runs 10psi with a clean filter and 18psi with a dirty filter, that represents the normal operating range. If pressure is below 10psi it indicates an obstruction in your suction side increasing head loss (clogged basket, jammed impeller, gopher stuck in skimmer). If pressure is above 18 psi it indicates an obstruction in your return side (closed valve, jammed heater flow control, clogged jets).

water dept uses a set up like your original drawing on fire lines
to detect use of water from the fire line [illegal taps]

it is NOT used to measure flow volume just if there is flow at all

btw most pool filters have a pressure gauge on them
replace the gauge with a pressure switch to turn on at a given pressure [the 18 psi]
and hook the switch to light bulb
that way a simple look will tell if you need to clean the filter [backwash] if the light is on
no new pipes or fitting or leaks ect

guess you could add a low switch to detect a full pump basket also

Quote:

Originally Posted by Amail (Post 9078369)

Thanks for the video. In there he shows pressure sensors on both the suction and discharge side of the pump. If you close off the pipe on the discharge side, I see how you get pressure (thanks, pump!). How do you get any pressure on the inlet side though? For instance, my pool water level is about a foot above the inlet of the pump, so I could see measuring a foot of head on the inlet side. But my friend's pool has the pump higher than the water level, so wouldn't it measure suction? :confused:

Suction on a centrifugal pump is measured in PSIA, not PSIG. Absolute pressure so it would be just under 15 psia at atmospheric pressure.
Then it would be converted to net positive suction head (required and available).

But that's a mute point (I know, it was on porpoise) because the suction on a swimming pool pump is going to be pretty stable, I can't see it changing much at all.